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Q.1-The p H of the body fluids is stabilized by buffer systems. Which of the following buffers is the most effective buffer system at physiological pH?                                 

a) Bicarbonate buffer                                                 

b) Phosphate buffer

c) Protein buffer                                                         

d) Deoxy hemoglobin

Q.2-Which of the following laboratory results below indicates compensated metabolic alkalosis?                                                                                                                  

a) Low p CO2, normal bicarbonate and, high pH     

b) Low p CO2, low bicarbonate, low pH

c) High p CO2, normal bicarbonate and, low p H     

d) High pCO2, high bicarbonate, High pH.

Q.3Which of the following has the highest glycemic index?                               

a) Ice cream                                                                

b) Cucumber

c) Bread                                                                     

d) Dextrose

Q.4-In diabetes mellitus there is reduced oxidation of carbohydrates; what will the effect of insulin administration on RQ?                                                                                

a)  It will increase                                                       

b) It will decrease

c) No effect                                                                

d) Initial rise and then fall

Q.5-Which of the following nutrients is rich in short and medium chain fatty acids

a) Milk                                                                        

b) Peanut oil

c) Sunflower oil                                                         

d) Almond oil

Q.6- A woman’s risk for developing breast cancer is greatest with:                   

a) Family history of breast cancer and a history of taking hormone replacement therapy

b) Early age at menarche and late age of first parity

c) A family history of breast cancer and a history of benign breast disease

d) A BRCA1 or BRCA2 mutation.

Q.7-Reduction of the 2′-hydroxyl of purine and pyrimidine Ribonucleotides, catalyzed by-

a) Thioredoxinreductase                                           

b) Ribonucleotide reductase

c) Dihydro folate reductase                                        

d) Oxidoreductase.

Q.8-Human brain has a low level of which of the following enzymes?               

a) PRPP synthetase                                                    

b) Amidotransferase

c) HGPRT                                                                  

d) Adenosine deaminase

Q.9- The fragments of newly synthesized DNA are sealed by enzymes referred to as –

 a) Restriction endonucleases                                     

b) Topo isomerases

c) Telomerases                                                

d) DNA ligases.

Q.10- In animal cells, including human cells, the replication of the DNA genome occurs only at a specified time during the life span of the cell. This period is referred to as the

a) gap 1(G1)                                                               

b) gap 2(G2)

c) M phase                                                      

d) S phase.

Q.11- The derepression of lac operon in the presence of lactose is an example of-        

a) Positive regulation                                                 

b) Negative regulation

c) Double negative regulation                                    

d) Double positive regulation.

Q.12- The operator locus is a region of double-stranded DNA-                          

a) To bind RNA polymerase                                      

b) To bind lac repressor

c) To bind CAP-cAMP complex                               

d) To bind transcription factors

Q.13- Which of the followings is not a stop codon in prokaryotes?                     

a) UAA                                                                      

b) UAG

c) UGG                                                                      

d) UGA

Q.14- The ideal support medium for separation of nucleic acids is-                    

a) Starch gel                                                               

b) Cellulose acetate

c) Agarose gel                                                            

d) Filter paper

Q.15- The drug Aspirin is detoxified by-                                                               

a) Methylation                                                            

b) Acetylation

c) Hydrolysis                                                              

d) Glucuronidation

Q.16- Which of the following enzymes is not a tumor marker?                           

a) Alkaline phosphatase                                             

b) Acid phosphatase

c) Lactate dehydrogenase                                          

d) Acid maltase

Q.17- DNA is assembled into nucleosomes with the help of special proteins called-

a) Prolamines                                                  

b) Histones

c) Chaperones                                                            

d) Protamines

Q.18- Burkitt’s lymphoma is caused by-                                                                

a) Adeno virus                                                                       

b) Human Papilloma virus

c) Hepatitis B virus                                                    

d) Epstein – Barr virus

Q.19- Which drug out of the following is not an anticancer drug?         

a) Azaserine                                                               

b) Allopurinol

c) Cytosine arabinoside                                              

d) Mercaptopurine.

Q.20- Which out of the followings is not a true mechanism for conversion of proto oncogenes to oncogenes?                                                                                               

a) Point mutation                                                       

b) Chromosomal translocation

c) Insertional mutagenesis                                          

d) Histone acetylation

 

 

Key to answers-

1)-a,2)-d,3)-d,4)-a,5)-a,6)-d,7)-b,8)-b,9)-d,10)-d,11)-c,12)-b,13)-c,14)-c,15)-c,16)-d,17)-b,18)-d,19)-b,20)-d

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Q.1- S- Adenosyl Methionine (Active Methionine )is required for the synthesis of all of the following compounds except-

a) Thymine                                                                 

b) Nor epinephrine

c) Epinephrine                                                            

d) Melatonin            

Q.2-Which out of the following compounds is not an inhibitor of complex IV of electron transport chain?

a) CO                                                                         

b) H2S

c) BAL                                                                       

d) CN.                        

Q.3-The inner mitochondrial membrane is rich in which of the following phospholipids?

a) Cardiolipin                                                             

b) Lecithin

c) Cephalin                                                                 

d) Plasmalogen         

Q.4The conversion of Pyruvate to Acetyl co A involves the participation of all except –
a) Niacin                                                                     

b) Riboflavin

c) Biotin                                                                     

d) Pantothenic acid.   

Q.5Which out of the followings is a fatty acid with 18 carbon atoms and one double bond in the trans configuration?

a) Palmitoleic acid                                                      

b) Oleic acid

c) Erucic acid                                                             

d) Elaidic acid.            

Q.6Which out of the followings is an ω 6 fatty acid?

a) Linolenic acid                                                        

b) Linoleic acid

c) Palmitic acid                                                          

d) Arachidic acid.     

Q.7-“Phospho enol pyruvate carboxy kinase”is an enzyme of which of the following pathway?

a) Glycolysis                                                              

b) Gluconeogenesis

c) Pentose phosphate pathway                                    

d) Glycogenolysis.    

Q.8-Which out of the followings is not a hemoprotein?

a) Tryptophan pyrrolase                                             

b) Tyrosinase

c) Myoglobin                                                              

d) Cytochrome P450. 

Q.9-Which of the following monosaccharides is not a carboxylic acid?

a) Glucuronate                                                                       

b) Gluconate

c) Glucose                                                                  

d) Muramic acid.       

Q.10 Which of the following apoproteins is an activator of lipoprotein lipase?

a) Apo A                                                                    

b) Apo B

c) Apo C II                                                                

d) Apo D.              

Q.11-Which of the following vitamins is used as a hypolipidemic drug?

a) Thiamine                                                                

b) Niacin

c) Folic acid                                                              

 d) Pantothenic acid     

Q.12-Malonyl co A is a direct inhibitor of which of the following enzymes of fatty acid oxidation?

a) Carnitine Acyl Transferase –I                                

b) Carnitine Acyl Transferase –II

c) Thiokinase                                                              

d) Thiolase             

Q.13-Which of the following enzymes requires adenosine triphosphate (ATP) for its action?

a) Argino Succinate lyase                                          

b) Argino Succinate synthetase

c) Arginase                                                                 

d) Glutaminase.    

Q.14-Which out of the followings is not a fibrous protein?

a) Carbonic anhydrase                                                           

b) Collagen

c) Fibrinogen                                                              

d) Keratin.                   

Q.15-Which of the following enzymes is not present in muscle?

a) Phosphorylase b                                                     

b) Hexokinase

c) Glucose-6-phosphatase                                          

d) Glycogen synthase 

Q.16-A 78-year-old male is brought to emergency with acute myocardial infarction. Blood biochemistry reveals lactic acidosis. How much energy yield (ATP) per mol of glucose is expected in such a condition?

a) 32                                                                           

b) 2

c) 34                                                                           

d) 36                      

Q.17-Pasteur effect is due to inhibition of glycolysis by high concentration of –

a) Creatine phosphate                                                

b) ATP

c) ADP                                                                       

d) AMP               

Q.18-The citric acid cycle is inhibited by which of the followings?

a) Fluoroacetate                                                         

b) Fluoride

c) Malonyl co A                                                         

d) Fluorouracil.           

Q.19-The key regulatory enzyme of HMP pathway is-

a) Glucose-6-P dehydrogenase                                

 b) Transaldolase

c) Transketolase                                                         

d) 6-P-Gluconate dehydrogenase.     

Q.20-A mutation has changed an Isoleucine residue of a protein to Glutamic acid, which statement best describes its location in a hydrophilic exterior-

a) On the surface since it is hydrophilic in nature

b) Inside the core of the protein since it is hydrophobic in nature

c) Any where inside or outside

d) Inside the core of protein since it has a polar but uncharged side chain.

 

Key to answers- 1)-b, 2- c, 3)-a, 4)-c, 5)-d, 6)-b, 7)-b, 8)-b, 9)-c, 10)-c, 11)-b, 12)-a, 13)-b,14)-a, 15)-c,16)-b,17)-b,18)-a,19)-a,20)-a

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Q.1- a) – What are sugar acids? Give examples of such acids and state their biological importance.        

Answer- Sugar acids are formed by the oxidation of –

1) Aldehyde group (C1) to form Aldonic acid, or

2) Primary Alcoholic group (C5) in an aldohexose to form uronic acid or

3) Both groups to form Saccharic acid.

Details of Reactions-

1)  Oxidation of Aldehyde group- Under mild conditions, in the presence of Hypobromous acid, the aldehyde group is oxidized to form Aldonic acid. Thus, Glucose is oxidized to Gluconic acid, Mannose to form Mannonic acid and Galactose to form Galactonic acid. Formation of Gluconic acid by the activity of Glucose oxidase is the basis for the Quantitative estimation of urinary and blood Glucose.

2) Oxidation of Primary Alcoholic acid- Under special conditions when the aldehyde group is protected, and the molecule is oxidized at the primary alcoholic group the product is a Uronic acid. Thus Glucose is oxidized to form Glucuronic acid, Galactose to form Galacturonic acid and Mannose is oxidized to Mannuronic acid. Glucuronic acid is used in the body for conjugation reactions to convert the toxic water insoluble compounds in to nontoxic water soluble forms, which can be easily excreted in urine. Glucuronic acid and its epimer Iduronic acid are used for the synthesis of heteropolysaccharides.

3) Oxidation of both Aldehyde and Primary Alcoholic group-Under strong acidic conditions (Nitric acid and heat)  the first and the last carbons are simultaneously oxidized to form dicarboxylic acids, known as Saccharic acids. Glucose is thus oxidized to form Gluco Saccharic acid, Mannose to Mannaric acid and Galactose to Mucic Acid .The mucic acid forms insoluble crystals and is the basis for a test for identification of Galactose.

b) What are Glycosides? Discuss the clinical significance of Glycosides

Answer- Acetal or ketal derivatives formed when a monosaccharide reacts with an alcohol are called glycosides. They are formed by the reaction of the hydroxyl group of anomeric carbon (hemiacetal or hemiketal) of monosaccharide with hydroxy group of second molecule with the loss of an equivalent of water.

The second molecule may be-

1) Another sugar (Glycon)- e.g. formation of disaccharides and polysaccharides.

2)  Non Carbohydrate (Aglycon)- such as Methanol, Glycerol, Sterol, steroids etc.

In naming of glycosides, the “ose” suffix of the sugar name is replaced by “oside”, and the alcohol group name is placed first. For example, D-glucose reacts with methanol in an acid-catalyzed process: the anomeric carbon atom reacts with the hydroxyl group of methanol to form two products, methyl α -D-glucopyranoside and methyl β -D-glucopyranoside. These two glucopyranosides differ in the configuration at the anomeric carbon atom. The new bond formed between the anomeric carbon atom of glucose and the hydroxyl oxygen atom of methanol is called a glycosidic bond specifically, an O-glycosidic bond

The anomeric carbon atom of a sugar can be linked to the nitrogen atom of an amine to form an N-glycosidic bond. Nucleosides are adducts between sugars such as ribose and amines such as adenine (the linkage between them is N-Glycosidic linkage).

Examples of Glycosides- Glycosides are present in many drugs, spices and in the constituents of animal tissues. Glycosides comprise several important classes of compounds such as hormones, sweeteners, alkaloids, flavonoids, antibiotics, etc. The glycosidic residue can be crucial for their activity or can only improve pharmacokinetic parameters.

1) Cardiac Glycosides

Cardiac glycosides all contain steroids as aglycone or genin component in combination with sugar molecules. These include derivatives of digitalis and strophanthus such as oubain.

2) Other glycosides such as streptomycin are used as antibiotics. Phloridzin is another glycoside which is obtained from the root and bark of apple tree. It blocks the transport of sugar across the mucosal cells of small intestine and also renal tubular epithelium. It displaces Na+ from the binding site of “carrier protein” and prevents the binding of sugar molecule and produces Glycosuria.

3) Glycosides of vitamins, both hydrophilic and lipophylic often occur in nature. Glycosylated vitamins have an advantage over the respective aglycone in their better solubility in water (especially the lipophylic ones), stability against UV-light, heat and oxidation, reduction of the bitter taste and odor (e.g., thiamine), and resistance to an enzymatic action. Some of the vitamin glycoconjugates have altered or improved Pharmacokinetic properties.

c) Discuss the structure and significance of Cellulose

 Cellulose- Cellulose is the chief constituent of plant cell walls. It is the most abundant of all carbohydrates .It is insoluble in water, gives no color with iodine and consists of β -D-glucopyranose units linked by β 1 →4 bonds to form long, straight chains strengthened by cross-linking hydrogen bonds. Mammals lack any enzyme that hydrolyzes the β 1→ 4 bonds, and so cannot digest cellulose. It is an important source of “bulk” in the diet, and the major component of dietary fiber. Microorganisms in the gut of ruminants and other herbivores can hydrolyze the linkage and ferment the products to short-chain fatty acids as a major energy source. There is some bacterial metabolism of cellulose in the human colon.

Figure- showing the structure of cellulose.

Cellulose yields Glucose upon complete hydrolysis. Partial hydrolysis yields cellobiose.

Products obtained from Cellulose-

  • Microcrystalline cellulose : used as binder-disintegrant in tablets
  • Methylcellulose: suspending agent and bulk laxative
  • Oxidized cellulose: hemostat
  • Sodium carboxymethyl cellulose: laxative
  • Cellulose acetate: rayon; photographic film; plastics
  • Cellulose acetate phthalate: enteric coating
  • Nitrocellulose: explosives; collodion (pyroxylin)

Q.2-a) What are storage polysaccharides? Give a brief description of each of them.

Answer- Glycogen, starch and Inulin are storage polysaccharides.

1) Glycogen- Glycogen is a readily mobilized storage form of glucose. It is a very large, branched polymer of glucose residues (Figure) that can be broken down to yield glucose molecules when energy is needed. Most of the glucose residues in glycogen are linked by α-1,4-glycosidic bonds. Branches at about every tenth residue are created by α–1,6-glycosidic bonds. It is the storage polysaccharide in animals and is sometimes called animal starch, but it is more branched than amylopectin present in starch.

 

 

Figure- showing the structure of glycogen.

It is hydrolyzed by both α and β-amylases and by glycogen phosphorylase. The complete hydrolysis yields glucose. Glycogen on reaction with iodine gives a red-violet color.

Glycogen is stored in muscle and liver. The concentration of glycogen is higher in the liver than in muscle (10% versus 2% by weight), but more glycogen is stored in skeletal muscle overall because of its much greater mass. Glycogen is present in the cytosol in the form of granules ranging in diameter from 10 to 40 nm. In the liver, glycogen synthesis and degradation are regulated to maintain blood-glucose levels as required to meet the needs of the organism as a whole. In contrast, in muscle, these processes are regulated to meet the energy needs of the muscle itself.

Glycogen is not as reduced as fatty acids are and consequently not as energy rich. But still animals store energy as glycogen? All excess fuel is converted is not converted into fatty acids. Glycogen is an important fuel reserve for several reasons.

The controlled breakdown of glycogen and release of glucose increase the amount of glucose that is available between meals. Hence, glycogen serves as a buffer to maintain blood-glucose levels. Glycogen’s role in maintaining blood glucose levels is especially important because glucose is virtually the only fuel used by the brain, except during prolonged starvation. Moreover, the glucose from glycogen is readily mobilized and is therefore a good source of energy for sudden, strenuous activity. Unlike fatty acids, the released glucose can provide energy in the absence of oxygen and can thus supply energy for anaerobic activity.

 2) Starch- It is a polymer of glucose, found in roots, rhizomes, seeds, stems, tubers and corms of plants, as microscopic granules having characteristic shapes and sizes. Most animals, including humans, depend on these plant starches for nourishment. The intact granules are insoluble in cold water, but grinding or swelling them in warm water causes them to burst. The released starch consists of two fractions.

About 20% is a water soluble material called amylose. The majority of the starch is a much higher molecular weight substance, consisting of nearly a million glucose units, and called amylopectin.

(a) Amylose is a linear polymer of α-D-glucose, linked together by α 1→4 glycosidic linkages. It is soluble in water, reacts with iodine to give a blue color and the molecular weight of Amylose ranges between 50, 000 – 200, 000.

 

Figure- showing the structure of Amylose

 (b) Amylopectin is a highly branched polymer, insoluble in water, reacts with iodine to give a reddish violet color. The molecular weight ranges between 70, 000 – 1 000, 000. Branches are composed of 25-30 glucose units linked by α 1→4 glycosidic linkage in the chain and by α 1→6 glycosidic linkage at the branch point.

 

Figure- showing the structure of Amylopectin

Hydrolysis: Hydrolysis of starch with hot dilute acids or by enzymes gives dextrins of  varying complexity, maltose and finally D-glucose

3) Inulin- Inulin is a polysaccharide of fructose (and hence a fructosan) found in tubers and roots of dahlias, artichokes, and dandelions. It is readily soluble in water and but it is not hydrolyzed by intestinal enzymes. It has a lower molecular weight than starch and colors yellow with iodine.It is used to determine the glomerular filtration rate, Inulin is of particular use as it is not secreted or reabsorbed in any appreciable amount at the nephron allowing GFR to be calculated, rather than total renal filtration.

b) Give a brief description of structure of proteins. Support your answer with suitable diagrams

Proteins perform complex physical and catalytic functions by positioning specific chemical groups in a precise three-dimensional arrangement. The polypeptide containing these groups must adopt a conformation that is both functionally efficient and physically strong. There are different levels of structural organization: Primary, Secondary, Tertiary and Quaternary.

1) Primary structure- Primary structure denotes the number and sequence of amino acids in the protein.  The sequence of amino acids is guided by the genetic information present on the DNA. A single nucleotide change in the DNA can bring about alteration in the amino acid sequence with the resultant loss of partial or complete loss of functional capacity of the protein. Example-  a  single nucleotide change in the genetic information for the synthesis of Beta globin chain of Hemoglobin results in the misincorporation of valine instead of glutamic acid  in sickle cell anemia   causing gross alterations in the oxygen carrying capacity of hemoglobin.

2) Secondary structure- Secondary structure is formed by the folding of short contiguous segments of polypeptide into geometrically ordered units. The following secondary structures are commonly found in  proteins

a) Alphahelix- The polypeptide backbone of an helix is twisted by an equal amount about each alpha carbon .A complete turn of the helix contains an average of 3.6 aminoacyl residues, and the distance it rises per turn (its pitch) is 0.54 nm (Figure-)The R groups of each aminoacyl residue in an helix face outward .Proteins contain only L-amino acids, for which a right-handed helix is by far the more stable, and only right-handed helices are present in proteins. The stability of an helix arises primarily from hydrogen bonds formed between the oxygen of the peptide bond carbonyl and the hydrogen atom of the peptide bond nitrogen of the fourth residue down the polypeptide chain. The ability to form the maximum number of hydrogen bonds, supplemented by van der Waals interactions in the core of this tightly packed structure, provides the thermodynamic driving force for the formation of an helix. Since the peptide bond nitrogen of proline lacks a hydrogen atom to contribute to a hydrogen bond, proline can only be stably accommodated within the first turn of an helix. When present elsewhere, proline disrupts the conformation of the helix, producing a bend. Because of its small size, glycine also often induces bends in helices. Charged amino acids , branched amino acids and the amino acids with a bulky side chain like Tryptophan are also not involved in the formation of alpha helix. Haemoglobin, myoglobin and alpha keratin proteins have most of their structure organized in the form of alpha helix.

b) Beta pleated sheets- The second (hence “beta”) recognizable regular secondary structure in proteins is the sheet. The amino acid residues of a sheet, when viewed edge-on, form a zigzag or pleated pattern in which the R groups of adjacent residues point in opposite directions. Unlike the compact backbone of the helix, the peptide backbone of the sheet is highly extended. But like the helix, sheets derive much of their stability from hydrogen bonds between the carbonyl oxygens and amide hydrogens of peptide bonds. However, in contrast to the helix, these bonds are formed with adjacent segments of sheet (Figure). Interacting sheets can be arranged either to form a parallel sheet, in which the adjacent segments of the polypeptide chain proceed in the same direction amino to carboxyl, or an antiparallel sheet, in which they proceed in opposite directions (Figure ). Either configuration permits the maximum number of hydrogen bonds between segments, or strands, of the sheet. Most sheets are not perfectly flat but tend to have a right-handed twist. Clusters of twisted strands of sheet form the core of many globular proteins.

c) Beta bends- Turns and bends refer to short segments of amino acids that join two units of secondary structure, such as two adjacent strands of an antiparallel sheet. A turn involves four aminoacyl residues, in which the first residue is hydrogen-bonded to the fourth, resulting in a tight 180-degree turn. Proline and glycine often are present in turns. The other amino acids are charged amino acids.

d) Loops and coils- Roughly half of the residues in a “typical” globular protein reside in helices and sheets and half in loops, turns, bends, and other extended conformational features. Loops are regions that contain residues beyond the minimum number necessary to connect adjacent regions of secondary structure. Irregular in conformation, loops nevertheless serve key biologic roles. For many enzymes, the loops that bridge domains responsible for binding substrates often contain aminoacyl residues that participate in catalysis. While loops lack apparent structural regularity, they exist in a specific conformation stabilized through hydrogen bonding, salt bridges, and hydrophobic interactions with other portions of the protein. However, not all portions of proteins are necessarily ordered. Proteins may contain “disordered” regions, often at the extreme amino or carboxyl terminal, characterized by high conformational flexibility. Coils are also there as part of structural components but they are longer than the loops and connect the adjacent secondary structures.

e) Super secondary structures- Beta – alpha –beta, Beta meanders and Greek key are the super secondary structures. Globular proteins are constructed by combining secondary structural elements These form primarily the core region and are connected by loop regions at the surface of the protein. Super secondary structures are usually formed by packing side chains from adjacent structural elements close to each other.

3) Tertiary structure- The term “tertiary structure” refers to the entire three-dimensional conformation of a polypeptide. It indicates, in three-dimensional space, how secondary structural features—helices, sheets, bends, turns, and loops—assemble to form domains and how these domains relate spatially to one another. A domain is a section of protein structure sufficient to perform a particular chemical or physical task such as binding of a substrate or other ligand. Other domains may anchor a protein to a membrane or interact with a regulatory molecule that modulates its function.

4) Quaternary structure- Quaternary structure defines the polypeptide composition of a protein and, for an oligomeric protein, the spatial relationships between its subunits or protomers. Monomeric proteins consist of a single polypeptide chain. Dimeric proteins contain two polypeptide chains. Homodimers contain two copies of the same polypeptide chain, while in a heterodimer the polypeptides differ. 

Examples- Immuno globulins are composed of 4 polypeptide chains, two light chain and two heavy chains , the enzyme Lactate dehydrogenase(LDH)  has two types of polypeptide chains arranged in the form of a tetramer, CPK(Creatine phosphokinase) enzyme has two polypeptide chains in its structure.

Forces stabilizing tertiary structure

Higher orders of protein structure are stabilized primarily—and often exclusively—by noncovalent interactions. Principal among these are hydrophobic interactions that drive most hydrophobic amino acid side chains into the interior of the protein, shielding them from water. Other significant contributors include hydrogen bonds and salt bridges between the carboxylates of aspartic and glutamic acid and the oppositely charged side chains of protonated lysyl, argininyl, and histidyl residues. While individually weak relative to a typical covalent bond of 80–120 kcal/mol, collectively these numerous interactions confer a high degree of stability to the biologically functional conformation of a protein.

Some proteins contain covalent disulfide (S—S) bonds that link the sulfhydryl groups of cysteinyl residues. Formation of disulfide bonds involves oxidation of the cysteinyl sulfhydryl groups and requires oxygen. Intrapolypeptide disulfide bonds further enhance the stability of the folded conformation of a peptide, while interpolypeptide disulfide bonds stabilize the quaternary structure of certain oligomeric proteins.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure- showing the levels of Protein structure

 

 

 

 

Q.3- Write short note on each of the followings-

a) Biologically important peptides-

The peptides of biological importance are as follows-

i) Glutathione-It is a tripeptide containing Glutamic acid, cysteine and Glycine. It participates in biological oxidation and reduction reactions.

ii) Carnosine- Dipeptide of β- Alanine and Histidine, present in muscles

iii) Anserine-is methyl Carnosine.

iv) Bradykinin- It is a nano peptide(contains 9 amino acids) , has a smooth muscle relaxant effect.

v) Oxytocin and vasopressin-Nano peptide hormones

vi) Angiotensins- Angiotensin I  (10 amino acids)is formed from Angiotensinogen by the action of Renin. Angiotensin II (8 amino acids) is formed from I by splitting of 2 amino acids, which is a potent vaso constrictor. It results in the formation of Angiotensin III which has 7 amino acids.

vii) Gastrin, Secretin and Pancreozymin- are gastro intestinal peptide hormones which affect secretion of bile and other digestive enzymes.

viii) β- Corticotrophin (ACTH), and β MSH are also peptide hormones

ix) Peptide Antibiotics- Penicillin, Gramicidin, Polymyxin, Bacitracins, Actinomycin, and Chloramphenicol are all peptide antibiotics.

x) Toxic peptides-Microcystine and Nodularin are lethal in large dosage.

xi) Anticancer peptides- Busulfan and cyclophosphamide

xii) Brain peptides-Dynorphin is a peptide containing 13 amino acids while met- enkephalin and Leuenkephalin(both pentapeptides) are brain peptides that reduce intestinal motility.

 

b) Conjugated Proteins

Conjugated proteins are simple proteins with a non protein prosthetic group. They can be classified as follows-

1) Glycoproteins- proteins with carbohydrate as the prosthetic group. The linkage may be  O-glycosidic linkage (with –OH group of serine and threonine or it can be N- Glycosidic linkage with amid group of Asparagine or Glutamine. When the carbohydrate content is  more than 10%, they are called Mucoproteins.

2) Lipoproteins -with lipid as the prosthetic group, examples are Chylomicron, VLDL, LDL, and HDL. The help in lipid transport in the aquatic plasma.

3) Nucleoproteins- proteins attached to nucleic acids e.g Histones attached to DNA.

4) Chromo proteins- proteins with colored prosthetic group. e.g. Hemoglobin, Myoglobin, Visual purple and Flavoproteins etc.

5) Phosphoproteins- Proteins with phosphoric acid as the prosthetic group, e.g. Ovovitellin of egg and Casein of milk are the examples of phosphoproteins.

6) Metalloproteins- Proteins with Metal as the prosthetic group, e.g. Carbonic anhydrase (Zinc),  Carboxypeptidase (Zinc) ,Superoxide dismutase (Zinc and copper), Xanthine Oxidase(Molybdenum) and Aconitase (Iron).

7) Haemoproteins- proteins with haem as the prosthetic group, e.g. Haemoglobin, Myoglobin, Tryptophan pyrolase, Catalase and peroxidase etc.

 

c) Isoelectric pH

The Isoelectric p H  is That p H at which the form of a molecule  has an equal number of positive and negative charges and thus is electrically neutral. The isoelectric pH, also called the pI, is the pH midway between pKa values on either side of the isoelectric species. Similar considerations apply to all polyprotic acids (eg, proteins), regardless of the number of dissociating groups present. In the clinical laboratory, knowledge of the pI guides selection of conditions for electrophoretic separations. For example, electrophoresis at pH 7.0 will separate two molecules with pI values of 6.0 and 8.0, because at pH 7.0 the molecule with a pI of 6.0 will have a net positive charge, and that with pI of 8.0 a net negative charge. Similar considerations apply to understanding chromatographic separations on ionic supports .

d) Derived amino acids

Derived amino acids are also called modified amino acids,  are classified in to two categories-

i) Derived amino acids found in proteins- examples include- Hydroxy Proline and Hydroxy Lysine, found in collagen. They are modified after translation. Gamma carboxylation of glutamic acid residues for clotting process and methylation or acetylation of histones to alter the gene expression are also examples of derived amino acids.

ii)  Derived amino acids not seen in proteins—examples include- Ornithine, Citrulline, Argino succinic acid , Homocysteine and GABA.  They are intermediary compounds of various metabolic pathways but are not found in proteins.

 

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 Paper II

Q.1. -Twenty multiple choice questions.         

Q.2. – Briefly describe the following-

a) Wobble hypothesis

b) Chemical carcinogenesis

c)  Nucleotide excision repair                                              

Q.3. –  Write short notes on-

a) Protein sparing effect of carbohydrates

b) Bicarbonate buffer system of blood

c)  15 minutes PSP excretion test

d)  Renal production and excretion of ammonia                  

Q.4. -a) Discuss in brief the causes, clinical manifestations and laboratory diagnosis of  AIDS.                                                                                    

 b) What is the cause of Orotic aciduria? Which pathway is most affected? Outline  the steps of that pathway and explain the basis of treatment of this disorder.

Q.5.-  Explain the principle, procedure and applications of –

a)  DNA finger printing

b)  ELISA

c)  Cloning of chimeric DNA                                                   

Q.6.- a) Discuss the significance of glucuronidation reactions of detoxification giving     examples.

b) Describe the process of excessive uric acid production by abnormal activities     of various enzymes. Explain the basis of using Allopurinol as a part of treatment   of hyperuricemia.

c) Describe in brief the mechanism of chromosomal translocation in the causation   of various cancers. Give suitable examples in support of your answer.                                                                                                                       

 

Multiple Choice questions

Q.1- Selenium poisoning can be cured by administration of:

a) Benzyl amines                                 

 b) p- Bromo Benzene                         

c) Acetanilide

d) p- nitro benzaldehyde         

 Q.2- Atrial Natriuretic peptide (ANP) produces all except-

a) Natriuresis                                       

b) Hypervolemia                                

c) Decreased blood pressure

d) Increased GFR.                 

 Q.3- All of the following are associated with metabolic acidosis except-

 a) Lactic acidosis                               

 b) Starvation                                      

c) Methanol poisoning

d) Prolonged diuretic therapy 

Q.4- Feeding of raw egg white will result in the deficiency of –

a) Biotin                                             

b) Thiamine                                        

c) Choline

d) Riboflavin                          

Q.5- The ideal tumor marker for the diagnosis of pheochromocytoma is-

a) Serotonin                                        

b) Catecholamines                              

c) Calcitonin

d) Insulin                                 

Q.6- If the p H of the blood is 7.4 then the ratio of [NaHCO3] to [H2CO3] will be-

a) 4:1                                                   

b) 10:1                                                

c) 20:1

d) none of the above.              

Q.7- Prolonged administration of Acetazolamide (Diamox) as a diuretic in a patient of congestive heart failure will produce-

a) Acidic urine                                               

b) Increase in NH4Cl excretion          

c) Alkaline urine

d) none of the above.             

 Q.8- All are causes of water intoxication except-

a) Renal failure                                

b) Excessive administration of fluids

c) Deficiency of Aldosterone

d) Hypersecretion of Aldosterone

Q.9- The binding of the prokaryotic DNA dependent RNA polymerase to promoter site is inhibited by-

 a) Streptomycin                                  

 b) Puromycin                                      

 c) Rifampicin

d) Tetracycline                      

Q.10-The mutagenesity of a compound can be detected by-

a) ELISA                                                       

b) Ame’s test   

c) Western blotting                                               

d) any of the above.    

 Q.11- A 20 year old man was diagnosed with abnormal form of β – globin (Hemoglobin Constant Spring) which is longer than the normal protein, which of the following point mutation is consistent with the abnormality?

  a) UAA——>CAA                                     

 b) CGA—–>UGA                                      

 c) UAA—->UAG

d) GAC—>  UAC   

Q.12- Antipyrin breath test is undertaken to diagnose underlying-

a) Hepatitis                                                  

b) Cancer                                                        

c) Tuberculosis

d) Renal failure.         

Q.13- Sudden increase in γ-GT in chronic Alcoholics indicates:

a) Hepatitis                                                     

b) Intrahepatic cholestasis                              

c) Recent bout of drinking alcohol

d) All of the above.     

Q.14- Urinary loss of Sodium occurs in-

a) Addison’s disease                                      

b) Chronic renal failure                                

c) Diabetic keto acidosis

d) All of the above     

Q.15- Carbonic anhydrase is absent in-

a) Parietal cells of stomach                           

b) Erythrocytes                                              

c) Plasma

d) Renal tubular epithelial cells.

State True or False

Q.16- High intestinal obstruction causes metabolic acidosis.                        

Q.17- If urine of specific gravity 1.020 or more contains 3.0gms NaCl/liter, salt depletion is present.                                                                                                         

Q.18- Serum Alkaline phosphatase level is abnormally low in obstructive jaundice.

Q.19- BMR is increased in Acromegaly.                                             

Q.20- Aspirin is mainly detoxified by oxidation.                                      

 Model Answers

Q.1- b,    2-b,      3-d,      4-a,      5-b,      6-c,      7-c,      8-c,      9-c,      10-b,    11-a,   

12-a,    13-c,    14-d,    15-c,    16- true,    17-true,    18-false,    19-true,

20-false.

 Q2- Briefly describe

a)  Wobble hypothesis- The mechanism by which the t RNAs can recognize more than one codon for a specific amino acid is described by the wobble hypothesis, in which the base at the 5’end of the anticodon (the first base of the anticodon) is not as spatially defined as the other two bases. Movement of that first base allows nontraditional base pairing with the 3’ base of the codon(the last base of the codon). This movement is called wobble and allows a single tRNA to recognize more than one codon. The result of the wobbling is that there need to be 61 codons coding for amino acids. (The examples of traditional and nontraditional base pairing are required to be given between the codon and the anticodon).

b)  Chemical Carcinogenesis- A large number of chemicals have been incriminated as carcinogenic. Some of them are direct reacting and some are procarcinogens and are converted to ultimate carcinogens in the body. The examples of chemical carcinogens are as follows-

1) Polycyclic aromatic hydrocarbons-Benzpyrene and dimethyl benzanthracene.

2) Azo- dyes(Aromatic amines)- β nephthyl amines, N- methyl -4- amino azo benzene, 2-acetyl amino fluorine.

3) Nitrosamines and Amides-Dimethyl nitrosamines, Diethyl nitroso amines.

4)  Naturally occurring compounds- Aflatoxin B1 produced by the fungus Aspergilus flavus.

5) Drugs- Alkylating and acylating agents e.g.- Cyclophosphamide, Busulfan.

diethyl stilbestrol, estrogen, Nitrogen Mustard, β- propiolactone.

6)   Miscellaneous agents- Beryllium, Cadmium, Nickel, chromium, Arsenic, Asbestos, vinyl chloride, saccharine and cyclamates.

Mechanism of chemical carcinogenesis- the chemicals can be-

Direct reacting-which can interact directly with the target molecule.

Procarcinogens- are not chemically reactive. In the body after metabolism they are converted to ultimate carcinogens which are highly reactive. This process of conversion is called metabolic activation. The enzyme systems involved in metabolic activation are cytochrome P450 species present in the endoplasmic reticulum of cells.

 DNA  is the primary and the most important target of chemical carcinogens. Hence chemical carcinogens are mutagens. The damage to DNA occurs can be-

–          binding covalently with DNA(also to RNA and proteins)

–          Interaction with purine, pyrimidines and phosphodiester groups of DNA

–          Most common site of attack is guanine .

 C) Nucleotide Excision repair-

The exposure of a cell to ultraviolet light can result in the covalent joining of two adjacent pyrimidines(Usually Thymines) producing a dimer. These thymine dimers prevent the DNA polymerase to further replicate the DNA strand beyond the site of dimer formation. The dimers are excised in prokaryotes by Nucleotide excision repair. The similar mechanisms operate in human beings.

  1. Recognition of dimer by UV specific endonuclease- First a UV specific endonuclease recognizes the dimer and cleaves the damaged strand at the 5’side of the dimer.
  2. Excision of damaged DNA-Next an excision endonuclease recognizes the incision made by the endonuclease. The stretch of the DNA containing the dimer is removed and the gap is filled by using the sister strand as a template by DNA polymerase. The nick is sealed by DNA ligase.
  3. Xeroderma pigmentosum-The pyrimidine dimers can be formed in the skin cells of humans exposed to UV light. In the rare genetic disease Xeroderma pigmentosum, the cells can not repair the damaged DNA strand, resulting in  extensive accumulation of the mutations and consequently skin cancers. The most common form of the disease is caused by the absence of the UV specific endonuclease.

Q.2- a) Protein sparing effect of carbohydrates-

Adequate amount of carbohydrates and fats in the diet may reduce the protein requirement. This may be due to metabolic products of carbohydrates such as oxaloacetate, pyruvate and alpha keto glutarate which provide the carbon skeleton for the formation of non essential amino acids through transamination. Carbohydrates reduce the requirement of the amino acids for gluconeogenesis. Both carbohydrates and fats are oxidized to produce energy and thus spare the proteins to be used for this purpose.

 b)Bicarbonate buffer system of blood

This consists of a weak acid “Carbonic acid and its corresponding salt with a strong base (Sodium bicarbonate).

Normal ratio in blood – NaHCO3: H2CO3– 20:1

They are the chief buffers of blood and constitute the Alkali reserve of the body. Neutralization of the strong acids and non volatile acids entering the ECF is achieved by the bicarbonate buffers. Such acids, e.g.- HCl. H2SO4, Lactic acid, etc which are strong and volatile react with NaHCO3 component forming H2CO3. Thus a strong and non volatile acid is converted to a volatile and weak acid, which is eliminated through alveoli of lungs. Hence bicarbonate buffer system is linked directly with respiration.

 Similarly when alkaline substance enters e.g. NaOH enters the ECF, it reacts with the acid component of the buffer system, and forming H2O.Thus the p H is maintained.

Advantages of bicarbonate system-

-It is present in very high concentration as compared to other buffers.

– Produces H2CO3 which is weak and volatile and CO2 ie exhaled out.

Thus it is a very good physiological buffer and acts as a front line defence.

Disadvantage of bicarbonate buffer

As a chemical buffer it’s a weak buffer as pKa is further away from the physiological pH 

 c) 15 minutes PSP excretion Test

This test is based on the fact that in the first 15 minutes 30 -50 % of the injected dye is excreted in urine which is an index of the adequate renal functions.

Test and interpretations-

When 1 ml of PSP(6mg) is injected IV, normal kidney will excrete 30-50% of the dye in first 15 minutes.

Excretion of less than 23% of the injected dye during this period regardless of the amount excreted in 2 hours indicates impaired renal functions.

It is also used to determine the function of each kidney separately. Here the appearance time and the rate of excretion of the dye are important. Increase in appearance time and the decrease in excretion rate indicate impaired renal functions.

 c) Renal production and excretion of ammonia-

Ammonia mechanism operates in the distal tubular cells, for the elimination of H+ ions and the conservation of Na+.

Sources of Ammonia-

1) Ammonia is produced by the hydrolysis of Glutamine by the enzyme Glutaminase which is present in these cells.

2) In addition NH3 is also produced from other amino acids by the oxidative Deamination by L- amino acid oxidase.

3)  It can also be formed from the glycine by the Glycine oxidase enzyme.

The NH3 thus formed forms Ammonium ion by combining with H+ ions and ammonium ion can exchange Na+ from NaCl.

The ammonia production is greatly increased in metabolic acidosis and is reduced in alkalosis. The activity of the Glutaminase enzyme is also enhanced in acidosis.. This mechanism is important for the conservation of the fixed bases.

Q4- a) AIDS is caused by a virus called Human Immuno deficiency virus. HIV belongs to the retrovirus group. They are RNA containing viruses that replicate with the help of the reverse transcriptase enzyme.75% of the total patients get this infection through sex. In about 15% of the patients the disease is transmitted through blood. Virus may be transmitted from mother to fetus through placenta. About 30% of the infants born of HIV positive mothers may get the infection.

Clinical presentations

Lymphadenopathy and fever may be seen at the end of the second stage. As the name indicates the basic defect lies in the immunodeficiency. This is mainly because the T helper cells are decreased in number. Since the immunity id deficient, non pathogenic micro organism enter the body and produce lesions in the skin, gastro intestinal tract, lungs, urinary tract and brain. Gastroenteritis and tuberculosis are the predominant pattern inIndia. In all the cases there is weight reduction and Kaposi’s sarcoma is also commonly associated with AIDS.

Laboratory Analysis

1)  The antibodies in the blood are detected by ELISA test, but there is a chance of false positive test, so all the positive cases are confirmed by Western Blot analysis. In ELISA the antibody against only one antigen (gp120) is tested, so there is probability of false result.

2)  In Western Blot analysis, antibodies against 6 different components of the virus are analyzed, so its confirmatory.

3)  T helper count is lowered. The normal level is more than 400/cmm. In AIDS patients the level is always is below 300/cmm. As the disease progresses the, the T helper count is correspondingly is lowered.

4)  In the last stages the p24 antigen starts rising.

5)  By Reveres transcriptase polymerase chain reaction, or by real time PCR, the number of HIV particles in blood can be estimated,  value of less than 5000 copies per ml of blood has good prognosis, while a count more than 100, 000 per ml means a very bad prognosis.

c)  Orotic aciduria

This condition results from absence of either or both of the enzymes, OPRTase and OMP decarboxylase. It is an autosomal recessive disease, characterised by retarded growth and megaloblastic anemia. The rapidly growing cells are most affected, hence there is anemiaCrystalsare excreted in urine, which may cause urinary tract obstruction. Due to the lack of feed back inhibition orotic acid production is excessive. The condition can be treated by feeding cytidine or Uridine. The may be converted to UTP which can act as feed back inhibitor.

This defect is associated with the pathway of Denovo pyrimidine synthesis.

Steps are to be mentioned.

 Q5- a) DNA finger printing

There are tandem repeats (VNTR) in chromosomes. The number of such repeats sites varies from person to person, but the number is unique for a given person. Therefore it serves as a molecular finger print. It is also known as a DNA profile. Probability of similarity between two persons is only 1 in 3×1010persons. DNA probes have been developed, so that at low stringency, they hybridize to a number of loci to produce individual specific finger prints. The technique is used identify the criminals and also used in disputes of parenthood. DNA can be isolated from the stains on clothing made by blood or semen stained even several years ago.

DNA finger printing is more applied in medico legal cases.

 b) ELISA

This Technique is widely used for detecting antigens, antibodies, estimating hormones, growth factors and tumor markers etc. This test is commonly employed to detect antigens or antibodies present in very small concentration in tissues or blood.

 Antigen detection by ELISA Method

 The specific antibody is fixed to the well of the micro titer plate. The patient’s serum is added to the well and incubated for 30 minutes at 37 degree centigrade. By this time if the serum contains antibodies it would have fixed to the well. Excess antigen and unwanted proteins are washed out and the antibody tagged with hose radish peroxidase is added. If the antigen is already fixed, the Ab-HRP conjugate will be fixed to the well. Then a color reagent containing hydrogen peroxide is added to the well. Color is developed. The development of the color indicates that the Ag is originally present in the patient’s serum. The intensity of the color formed is proportional to the amount og the antigen present in the given sample.

Based on the specific affinity the antibodies can also be detected by this method.

 c) Cloning of chimeric DNA- cloning allows the production of a large number of identical molecules. The steps involved are-

1)  Preparation of chimeric DNA molecules

2) Transfection of the vector in to the host

3)  Selection of the colony carrying the desired genes

4)  Amplification of the gene.

All steps are to be elaborated with diagrams. The applications of this technology in the field of medicine, agriculture and industrial fields are to be discussed in brief.

 Q.6- a) Glucuronidation reactions of detoxifications

These reactions are for the detoxification of toxic substances. UDP Glucuronic acid is formed in the uronic pathway. Glucuronyl transferase is the enzyme responsible for the detoxification reactions. Various substances that are conjugated with Glucuronic acid are as follows-

1) Bilirubin to form bilirubin diglucuronide.

2) Aromatic acids e.g.- Benzoic acid

3)  Phenols and other secondary and tertiary aliphatic alcohols

4)  Morphine, menthol, acetanilide, sulfa, pyridine etc.

5)   Hormones like thyroid hormones, derivatives of steroids etc

 b) Hyperuricemia by abnormal activities of enzymes

The activities of PRPP synthetase, amido transferase, HGPRTase, Glucose-6 phosphatase and Glutathione reductase are to be mentioned.

The use of Allopurinol as a competitive inhibitor of Xanthine oxidase is to be mentioned.

 d) Chromosomal Translocation- Most of the tumor cells show chromosomal abnormality, in which a piece of one chromosome is split off and joined to another chromosome. If the second chromosome also donates the piece to the first then is is called reciprocal translocation.

The examples of Burkitt’s lymphoma, chronic granulocytic leukemia are to be mentioned with diagrams.

 

 

 

 

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Q.1-20 multiple choice questions .

Q-2- a) Describe the reaction catalyzed by phosphofructo kinase-1 enzyme and explain how is it regulated?                                                                           

b) Give a diagrammatic representation of sites of ATP formation and inhibitors of the mitochondrial Electron Transport Chain.                                                                                                                      

Q.3- a) Describe various mechanisms of enzyme inhibition. Mention the clinical uses of enzyme inhibitors.                                                                  

b) Describe the steps of urea formation and discuss the mechanism of ammonia  intoxication of brain.                                                                          

Q.4-  a) Explain the causes, clinical manifestations and laboratory diagnosis of-

 i) Albinism                 

ii) Von Gierke’s disease                                  

b) Calculate the energy yield from the complete oxidation of one molecule of  glucose under aerobic conditions.                                                      

Q.5- a) Describe the steps of beta oxidation of fatty acids. What is the clinical  significance of this pathway?                                                             

b) Give a diagrammatic representation of structure of a lipoprotein molecule.

c) Discuss the causes, and effects of denaturation of proteins.       

Q.6- Write short note on-

a) Vitamin C deficiency

b) Rancidity

c) Lipotropic agents                                                                           

d) Cori’s cycle                                                                         

Multiple Choice questions

Q.1- Acetyl co A carboxylase enzyme requires ————— as a coenzyme.

a) FMN                                               

b) Biotin  

c) NAD+                                          

d) TPP                   

Q.2- All are intermediates of glycolysis except-

a) Glucose-6 phosphate                       

b) Fructose 1, 6 bisphosphate         

c) Fructose-6- phosphate

d) Glycerol – 3- phosphate 

 Q.3- In the de novo synthesis of fatty acids, Acetyl co A first gets converted to –

a) Mevalonate                                     

b) Malonyl co A      

c) Malonate

d) D-Methyl malonyl co A 

Q.4- All of the following compounds are synthesized from Tyrosine except-

a) Melanin                                                      

b) Catecholamines                                          

c) Thyronine

d) Creatinine                           

Q.5- Which of the following is predominantly required for coagulation of blood-

a) Sodium                                            

b) Calcium         

c) Potassium                                 

d) Magnesium                        

Q.6- Hemoglobin is a

a) Nucleoprotein                                 

b) Glycoprotein                                  

c) Phosphoprotein

d) Chromo protein                

Q.7- Cholesterol is a precursor of all except-–

a) Bile pigment                                    

b) Sex hormones                                

c) Vitamin D

d) Corticosteroids                 

Q.8- Phospholipase A2 can be found in –

a) Pancreatic juice                               

b) Gastric juice                                   

c) CSF

d) Amniotic fluid                  

Q.9-The disease resulting from vitamin B12 deficiency is-

a) Pernicious anemia                           

b) Night blindness                              

c) Beri-Beri

d) Scurvy                                

Q.10- Serotonin is synthesized from which of the following amino acid?

a) Phenylalanine                               

b) Glycine                                          

c) Tryptophan

d) Methionine                        

 Q.11- Prostaglandins are synthesized from –

a) Arachidonic acid                             

b) Stearic acid                                    

c) Palmitic acid

d) Oleic acid                           

Q.12- The biochemical defect in Niemann–pick disease, is deficiency of-

a) Glucose-6 –phosphate dehydrogenase       

b) Hexosaminidase –A                                   

c) Glucose-6-phosphatse

d) Sphingomyelinase   

Q.13- In an enzyme assay, in which the substrate concentration is much higher than Km, the rate

a) Approaches half Vmax                

b) Shows first order kinetics              

c) is independent of enzyme concentration

d) shows zero order kinetics 

 Q.14- Formation of UDP Galactose from Galactose-1-P is catalyzed by-

a) Hexokinase                                     

b) Aldolase                                         

c) Galactokinase

d) Galactose-1-P Uridyl transferase 

Q.15- All are found in obstructive jaundice except-

a) Conjugated hyperbilirubinemia       

b) Bilirubinuria                                   

c) Raised Alkaline phosphatase

d) Dark tarry stools                

Q.16- The excretion of which of the following compound is greatly increased in urine in Carcinoid syndrome-

a) Indole acetic acid                           

b) 5- hydroxy Tryptamine                  

c) 5- hydroxy tryptophan

d) 5- Hydroxy Indole acetic acid       

Q.17- The iso electric p H of which of the following proteins is 4.6-

a) Zein                                                 

b) Casein                                            

c) Keratin

d) Myosin                                       

Q.18- The reaction catalyzed by- Lactate dehydrogenase is-

a) Pyruvate <—————————–> Lactate

b) Pyruvate—————————–>Oxaloacetate

c)  Pyruvate—————————-> Acetyl Co A

d) Pyruvate—————————->Acetaldehyde                                 

Q.19- The key regulatory enzyme of HMP pathway is-

a) G- 6-phosphate dehydrogenase      

b) Transaldolase                                 

c) Transketolase

d) G-6-phophatase               

Q.20- Pellagra is caused by nutritional deficiency of-

a) Vitamin B12                                     

b) B6                                                   

c) Niacin

d) Folic acid                          

 

  Model Answers- Paper -I

Q.1- Multiple Choice Questions-

1-b

2-d

3-b

4-d

5-b

6-d

7-a

8-a

9-a

10-c

11-a

12-d

13-d

14-d

15-d

16-d

17-b

18-a

19-a

20-c

Q2- a) Reaction catalyzed by phosphofructo kinase-1 enzyme – This is the rate limiting enzyme of glycolysis. It catalyzes the formation of Fr 1,6 bisphosphate from Fr-6-p.It is regulated by substrate concentration, product inhibition, allosteric modification and by induction or repression. Insulin favours while glucagon and catecholamines inhibit glycolysis. Hypoxia also stimulates glycolysis. Allosterically fr-2,6 bisphosphate acts as a positive modifier while ATP acts as negative modifier.

Details are needed

b)  A diagrammatic representation of sites of ATP formation and inhibitors of the mitochondrial Electron Transport Chain- The four complexes of ETC are to be represented showing the entry of reduced coenzymes, and the sites of ATP formation . The sites of site specific inhibitors are to be shown.

Q.3- a) Mechanisms of enzyme inhibition- Enzymes can be inhibited by-

a)  Competitive inhibition

b) Non Competitive inhibition

c) Un Competitive inhibition

d) Allosteric inhibition

Clinically enzyme inhibitors are used as drugs for the treatment of various diseases. The role of ACE inhibitors  for the treatment of hypertension, Methotrexate and various other  for cancers, Statins for hypercholesterolemia, Sulphonamides, Trimethoprim and Penicillin as antibacterial agents etc are to be referred mentioning the inhibition of the specific enzymes.

3-b) Steps of Urea formation- Urea is formed in liver from Ammonia and CO2, which condense together to form Carbamoyl- phosphate in the presence of CPS-I enzyme. Carbamoyl- phosphate further condenses with ornithine to form Citrulline. Citrulline condenses with aspartic acid to form Argino succinic acid which is subsequently cleaved to form Arginine and fumarate. Fumarate is converted to malate, then to Oxaloacetate, which is transaminated to form Aspartate. Aspartate can re enter the cyclic pathway. On the other hand Arginine is cleaved to form Ornithine and urea. Ornithine can be reutilized for the continuation of the cycle.

Reactions are to be shown

Ammonia is toxic to brain, as it depletes Alpha keto glutarate, and glutamate resulting in depression of TCA cycle and reduced formation of GABA the inhibitory neurotransmitter. Glutamine level is increased which is transported out in return for Tryptophan. Tryptophan is a precursor for serotonin, an excitatory neurotransmitter. All these result in energy depletion due to depression of TCA cycle and hyperexcitaion due to excessive Serotonin production. Convulsions and coma are the signs on ammonia intoxication. Death occurs in untreated cases.

Q.4- a) i) Albinism- is a disorder of Tyrosine metabolism. There is deficiency of Tyrosinase enzyme; as a result there is impaired formation of Melanin. The affected patients show depigmentation of iris, skin and hair. Based on the type of defect, Albinism can be ocular, occulocutaneous or partial. Diagnosis is made by clinical manifestations and by estimation of Tyrosinase enzyme in cultured cells. No permanent cure only symptomatic treatment can be imparted.

ii) Von-Gierke’s disease- It is a type 1 glycogen storage disease. The defect lies in the deficiency of Glucose-6 phosphatase enzyme. There is impaired glycogen degradation and hence normal glycogen gets abnormally accumulated in liver, intestine and kidney. Hypoglycemia is a characteristic finding. Short stature, protuberant abdomen, pallor, bleeding tendencies and impairment of liver and kidney functions are typical of this disease. Hyperuricemia, hypoglycemia and lactic acidosis are diagnostic. No permanent cure, only symptomatic treatment is given.

Details are needed

b) Energy yield from the complete oxidation of one molecule of glucose under aerobic conditions-38 ATPs are produced from the complete oxidation of one molecule of Glucose. The details of energetic of Glycolysis, Pyruvate dehydrogenase complex and the oxidation of Acetyl co A in TCA cycle are to be mentioned.8 ATPs in glycolysis, 6 in PDH complex and 24 ATPs in TCA cycle are produced making a total of 38 ATPs.

Q.5-a) Steps of beta oxidation of fatty acids-

Activation to form Acyl co A, internalization to mitochondrial matrix through carnitine shuttle and the subsequent steps of beta oxidation in the form of dehydrogenation, hydration, dehydrogenation and thiolytic cleavage are to be mentioned. The total energy yield is to be explained. The clinical significance lies in medium chain acyl co A dehydrogenase deficiency and carnitine deficiency producing hypoglycemia due to imbalance between demand and supply of energy.

b) Structure of lipoprotein molecule- Lipoproteins are conjugated proteins for the transportation of lipids. The hydrophilic exterior of lipoprotein is made by apoproteins, free cholesterol and by phospholipids while the hydrophobic core is constituted by triglycerides, cholesteryl ester etc. All have to be represented by a clean diagram.

c) Denaturation- The process of disruption of the secondary, tertiary or quaternary structure if present of proteins is called Denaturation. The primary structure remains intact. Application of heat, strong acids, strong alkalies, heavy metal salts and physical factors like vigorous shaking and freezing can bring about Denaturation. The Denaturation in most cases is irreversible but it can be reversible also as in iso electric p H pecipitation or denaturation of Ribonuclease in the presence of urea.

 Protein loses its biological property on Denaturation. There is total functional loss on Denaturation. Details are to be provided for the types and effects of Denaturation.

 Q.6- a) Vitamin C deficiency is manifested in the form of scurvy, which is characterized by bleeding tendencies, bony changes and microcytic hypochromic anemia. Causes, detection of deficiency and treatment are to be mentioned

 b) Rancidity- It is the unpleasant smell and taste given by fats when kept for a long time or exposed to air. It is due to partial hydrolysis or oxidation of fats producing fatty aldehydes. Anti oxidants can be added to prevent rancidity. Brief reference of lipid peroxidation is also required to be mentioned.

c) Lipotropic agents- Essential fatty acids, choline. Betaine, methionine, vitamin B6, B12 and folic acid are called as lipotropic agents. They are so called lipotropic agents as they prevent the deposition of fats in liver cells and promote fat mobilization from liver to peripheral tissues. Deficiency of these factors produces fatty liver.

d) Cori’s cycle- Transportation of  lactate from muscles through blood to liver for conversion to glucose and transportation of glucose from liver  back to muscles for utilization in the glycolytic pathway for energy production and production of lactate  which is transported to liver again and again in the same way, this constitutes cori’s cycle. It is meant for disposal of waste product of muscle i.e. lactate for glucose production. Accumulation of lactate in muscles produces fatigue,

 

 

Paper II

Q.1- 20 multiple choice questions ,                    

Q.2-  a) What is the significance of maintenance of p H in body? Give a brief   account of role of kidneys in the regulation of acid and base balance of the  body.                                                                                                  

b)  Briefly discuss the role of ATP in the biological   system.          

c) Discuss the biochemical basis of hyperuricemia in HGPRTase deficiency.

Q.3-a) Discuss the salient features of Transcription of DNA.                  

b) Briefly discuss about post translational modifications.                  

c) What are the possible causes of DNA damage? How is this damage repaired?   

 Q.4-  a) Give a detailed account of Respiratory acidosis, mentioning the possible  causes, alterations in laboratory profile, compensation by the regulatory    mechanisms and the consequences in untreated cases.                                                                                                                                                                     

b) Describe the role of Renin -Angiotensin system in the maintenance of water and electrolyte balance of the body;                                                         

Q.5-  a) Discuss the causes of Protein energy malnutrition. What are the possible risk factors associated with it and how can this be treated?       

b) A 20 year-old drug addict has reported to emergency complaining of fever,   cough,  diarrhea and weight loss from the last few months. He is too weak to walk. There is a suspicion of HIV infection. How will you proceed for the diagnosis? What seems to be the possible cause for HIV infection in this patient? What are  the various modes of transmission of HIV infection?                

Q.6- Write short note on-

 a) Biochemistry of cancer cells          

 b) Galactose tolerance test

 c) Thin layer chromatography                                                          

 

Multiple Choice questions

Q.1- In protein synthesis which out of the following is a termination codon?

a) UAU                                              

b) UAC       

c) UGA                                       

d) UGG                       

 Q.2- A promoter site on DNA –

a) is present upstream to the start site           

b) is present on the coding strand     

c) Initiates transcription              

d) All of the above     

Q.3- All are true for DNA polymerase except one-

a) Has exonuclease activity

b) Works only in 5`to 3` direction

c) Edits as it synthesizes

d) Synthesizes RNA primer to initiate DNA synthesis.       

Q.4- Which of the following result is provided by Western Blot Analysis

a) Detects DNA molecules             

b) Detects Protein molecules             

c) Detects RNA molecules

d) Determines chromosomal structure

Q.5- Which of the following is an anticancer drug?

a) 5- methyl thymidine                      

b) Ribose phosphate                           

c) Ara C

d) PRPP (5- phosphoribosylpyrophosphate)

Q.6- All are true regarding Nephrotic syndrome except-

a) Hypoglycemia                               

b) Proteinuria          

c) Edema                          

d) Hypoproteinemia    

 Q.7- Urinary finding in Starvation is

a) Glycosuria                                    

b) Ketonuria                                       

c) Proteinuria

d) oliguria        

 Q.8- What is true of Diabetes Insipidus?

a) High specific gravity of urine         

b) Oliguria                                          

c) Deficiency of ADH hormone

d) Glycosuria

Q.9- LDH is increased in-

a)Acute MI                                         

b) Hemolytic anemia                          

c) Liver diseases

d) All of the above.  

Q.10- Approximately ———– of bile acids are excreted in feces per day

a) 2 00 G                                            

b) 200 mg

c) 400 G                                             

d) 400 mg               

Q.11- Essential fatty acids can be synthesized in-

a) Human beings                              

b) Animals                                          

c) plants

d) None of the above 

Q.12- A condition where the amount of nitrogen lost from the body exceeds the dietary intake is called as:

a) Negative nitrogen balance              

b) Nitrogen equilibrium      

c) Positive nitrogen balance                

d) Uremia.                  

Q.13- Which of the following sugar is found in RNA?

a) 2- deoxy Ribose                              

b) 3-deoxy Ribose  

c) D- Ribose                            

d) D- Xylulose                       

Q.14- Congenital absence of Adenosine deaminase causes-

a) Immunodeficiency                         

b) Hyperglycemia                              

c) Hyperuricemia

d) Hyperoxaluria       

Q.15- All are nucleosides except-

a) Cytosine                                        

b) Guanosine                                      

c) Inosine

d) Adenosine             

Q.16- An anxious, nervous female was breathing rapidly. What do you expect the acid base status of the body?

a) Metabolic acidosis                      

b) Metabolic alkalosis      

c) Respiratory acidosis                  

d) Respiratory Alkalosis 

Q.17- Periods of prolonged starvation will produce what type of acid base alteration in the body?

a) Metabolic acidosis                          

b) Metabolic alkalosis                        

c) Respiratory acidosis

d) Respiratory Alkalosis

Q.18- All are inhibitors of protein synthesis except-

a) Streptomycin                                               

b)Erythromycin                                              

c) Oligomycin

d) Tetracycline                      

Q.19- All of the following are observed in high fibre diet except-

a) Reduced incidence of constipation

b) Decrease in blood cholesterol

c) Increased frequency of hyperglycemia

d) Decreased risk of colon cancer                                                       

Q.20-If there is an increased concentration of glucose in urine, the most likely cause could be

a) Starvation                                        

b) Alcoholism                                     

c) Diabetes mellitus

d) Hepatitis          

 

Model Answers- Paper- II

 Q.1-Multiple choice questions

1-c

2-d

3-d

4-b

5-c

6-a

7-b

8-c

9-d

10-d

11-c

12-a

13-c

14-a

15-a

16-d

17-a

18-c

19-c

20-c

 

Q.2-a) Significance of maintenance of p H in the body- p H maintainenance is required for the proper functioning of proteins, enzymes, DNA, nerve conduction ,muscle contraction, as well as for the flow of substances across the membranes. Blood buffers, lungs and kidney play a significant role in the maintenance of body p H. Kidneys promote excretion of H+ and reabsorption of bicarbonate ions depending on acid base status of the body. The bicarbonate, phosphate and ammonia mechanisms are required to be explained giving diagrammatic representations.

b) Role of ATP in the biological system- ATP is considered the energy currency of cell. Various examples of exergonic reactions are to be mentioned. Sources of ATP i.e. from oxidative phosphorylation and substrate level phosphorylation are to be mentioned.

c) Biochemical basis of hyperuricemia in HGPRTase deficiency- HGPRTase deficiency is manifested as Lesch Nyhan syndrome. Hyperuricemia is due to non utilization of PRPP which in turn is used for Denovo synthesis of purine nucleotides. Purines can not be utilized by Salvaged pathway; hence they are catabolized to form uric acid. Excess synthesis and catabolism of purines is the cause of hyperuricemia in this defect.

 Q.3- Salient features of Transcription of DNA

I) Transcription process includes initiation, elongation and termination.

2) There are specific sites on DNA that act as start signals for initiation process. The RNA polymerase attaches at the promoter site on the template strand.

3)The region between promoter and terminator  sites on DNA site is called as Transcription unit, which is transcribed in to mRNA.

4) Bacterial RNA polymerases differ from eukaryotic  RNA polymerases.

5) One of the strand acts as a template and the base pairing rule is followed.

6) There is no proof reading, hence less fidelity is there.

7) Specific signals are recognized for termination by termination protein, the Rho    factor. The termination can also be Rho independent.

8) The primary transcript thus formed undergoes post transcriptional modifications.

b) Post translational modifications- The mature functional protein is formed by the post translational processes, which include the following processes-

1) Proteolytic cleavage

2) Modification of the amino acids

3) Sub unit aggregation etc. are to be discussed with suitable examples. 

c) DNA damage and repair

Following are the possible causes of DNA damage –

1) Misincorporation of deoxy ribonucleotides during replication

2) Spontaneous Deamination of bases

3) From X- Rays that cause nicks in the DNA

4) From UV radiations that cause Thymine dimer formation

5) From various chemicals that interact with the DNA

Mechanisms of repairSeveral methods are there –

1)      Excision repair

2)      Photo reactivation

3)      Recombinational repair

4)      Mismatch repair

Q.4-a) Respiratory acidosis

Primary excess of carbonic acid produces respiratory acidosis. Respiratory acidosis may result from bronchopneumonia or status asthmaticus. Depression of respiratory centre by sedatives or narcotics; chronic obstructive pulmonary diseases etc cause difficulty in breathing resulting in retention of carbonic acid. Renal compensation occurs by excretion of more H+  and retention of bicarbonates.

Alterations in p H, blood gas analysis etc to be mentioned.

Treatment depends on the primary cause.

 Details are needed

b) Role of Renin -Angiotensin system in the maintenance of water  and electrolyte balance of the body- Renin is a proteoltic enzyme released from the kidney. It is released in response to the fall in sodium ion concentration, Hypovolemia, hypotension and a fall in intra cellular calcium ion conc., All these factors  stimulate the release of Renin from J.G. cells to blood. The action of Renin is mediated through the release of Angiotensin I from Angiotensinogen. Angiotensin I  is then converted to Angiotensin II and then to Angiotensin III. Both the later Angiotensins cause the release of Aldosteron from the Adrenal cortex, which causes the absorption of Sodium ions to restore the blood pressure and the fluid volume. The interdependence of Renin- Angiotensin system and the Aldosteron is to be discussed. The clinical significance and the use of ACE inhibitors for the treatment of Hypertension are to be discussed.

Q.5- a) Protein energy malnutrition

At one end of the spectrum is Marasmus which results from a continued and the severe deficiency of both dietary energy and proteins (primary calorie in adequacy and Secondary protein deficiency). At the other end of the spectrum is Kwashiorkor, where isolated deficiency of proteins along with adequate calorie intake is seen.

A brief description of the causes, clinically symptoms and laboratory findings is to be given. The possible treatment is also required to be mentioned.

b) Transmission of HIV- The various routs like the blood, placenta, sex etc are to me mentioned. The cause of HIV infection in this patient seems to be drug abuse.

Q.6-a) Biochemistry of cancer cells- cancer cells are characterized by three important properties-Diminished or unrestricted growth, Capability of invasion of local tissues and capability of spread to distant places by metastasis . The characteristics of cancer cells – the morphological and biochemical changes are to be discussed.

b) Galactose tolerance test- It is an index of impaired liver functions. When galactose load is given , it is  exclusively metabolized in liver and is converted to glucose The rate of utilization is proportional to functional liver cell mass. Details of procedure and observations in cirrhosis of liver and infective hepatitis are to be mentioned.

c) Thin layer chromatography

This is another version of the liquid- liquid chromatography. A thin layer of the silica gel is spread on a glass plate, biological sample is applied as a small spot .T he plate is placed in a trough containing the solvent.. The stationary water phase is held on the silica gel and the mobile phase of non polar solvent moves up. In the case of TLC it takes only 3-4 hours for the separation of the substances in comparison to Paper chromatography which takes 14-16 hours, that is a distinct advantage for TLC.

 

 

 

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Q.N.1- 20 multiple choice questions on a separate sheet.              
Q.N.2- a) What are the salient features of an a-helix? Name two amino acids that destabilize this structure.                                                                  

b) Give an account of the biochemical changes in the blood of a phenylketonuric subject. How will you proceeds for the diagnosis and treatment of this disease? 

c) Outline 3 metabolic roles of glycine.                                

Q.N.3– a) Describe the steps of de novo synthesis of fatty acids? How is this process regulated?                                                                                      

b) Explain the significance of the enzyme b-hydroxy-b-methylglutaryl CoA (HMG-CoA) Reductase.                                                                 

Q.N.4- a) Explain why are the following compounds toxic: (i) Rotenone (ii) 2, 4-dinitrophenol (iii) Atractyloside.                                                            

b) Explain how alcohol consumption by an undernourished person can cause hypoglycemia.                                                                                             

c) Explain why the breath of an untreated diabetic smells of acetone.

 d) Explain how the monitoring of glycosylated hemoglobin (HbAIc) levels is useful in the treatment of diabetes mellitus.                                          

Q.N.5- Write short notes on-                                             

a) Visual cycle

b) One carbon metabolism.

c) Enzyme Inhibition

Q.N.6- a) Briefly discuss the mechanism of iron absorption from the intestinal lumen. What is its biological and clinical significance?                       

b) Give an example of:

(i) cyclic fatty acid

(ii) polyunsaturated fatty acid and

(iii) Glycolipids.                                                                                      

 c) Give the biochemical explanation for the presence of high levels of (i) Ketone and (ii) Methylmalonic acid in the urine.                            

 

Multiple Choice Questions

Q.N.1- Which of the following monosaccharide is not an aldose?

a) Ribose                                                                    

b) Glucose

c) Fructose                                                                 

d) Glyceraldehyde.    

Q.N.2- Which of the following enzymes catalyzes a reaction that involves a decarboxylation reaction?

a).Pyruvate dehydrogenase                                

b) Isocitrate dehydrogenase

c) α-keto glutarate dehydrogenase                    

d) all of the above.     

Q.N.3- In the enzyme catalyzed reactions when the conc. of the substrate is too high the reaction order is-

a) Zero order                                                              

b) First order

c) Second order                                                        

 d) Third order.                       

Q.N.4-. The primary defect which leads to sickle cell anemia is:

a)An abnormality in porphyrin part of hemoglobin.

b Replacement of glutamate by Valine in β-chain of HbA.

c).A nonsense mutation in the β -chain of HbA.

d)Substitution of Valine by glutamate in the α -chain of HbA.                     

Q.N.5-Which of the following is a sugar alcohol?

a) Gluconic acid                                                      

b) Mannitol

c) Maltose                                                                 

d) Xylulose                

Q.N.6- In Tangier’s disease-

a) HDL is more in plasma                                     

b) HDL is less in plasma

c) LDL is more in plasma                                      

d) LDL is lesst in plasma.

Q.N.7- All are nitrogen containing compounds except-

a) Catecholamines                                                 

b) Thyroid hormones

c) Creatine                                                                

d) Fructose-6-phosphate. 

Q.N.8- Absorption of calcium is enhanced by the presence of vitamin-

a) A                                                                              

b) D

c) K                                                                              

 d) B1                       

Q.N.9- All are proteins that include a porphyrin ring except-

a) Catalase                                                               

b) Myoglobin

c) Fibrinogen                                                          

d) Cytochrome          

Q.N.10-Enzymes of TCA cycle are found in-

a) Cytoplasm                                                            

b) Mitochondria

c) Lysosomes                                                            

d) None of the above.         

Q.N.11- Histidine is catabolized by opening the ring to produce-

a) Formimino Glutamic acid                              

b) Ornithine

c) γ-amino butyric acid                                        

d) p- amino benzoic acid 

Q.N.12-Which metal is responsible for imparting red color to vitamin B12-

a) Magnesium                                                          

 b) Cobalt

c) Chromium                                                              

d) Zinc                                   

Q.N.13- Zinc is a part of the structure of the following enzyme-

a) Pepsin                                                                      

 b) Carbonic Anhydrase

c) Trypsin                                                                      

d) Cytochrome Oxidase.

Q.N.14- Pellagra is characterized by-

a) Gastroenteritis                                                          

b) Osteomalacia

c) Aplastic anemia                                                        

d) Exfoliative dermatitis.

Q.N.15- Creatine is present in urine in-

a) Thyrotoxicosis                                                        

 b) Starvation

c) Myasthenia Gravis                                                    

d) All of the above.   

 State True or False

Q.N.16- Tay Sach’s disease is a Glycogen Storage disease.                          

Q.N.17- Serotonin is derived from Tryptophan.                                      

Q.N.18-Ammonium ion is toxic to the brain.                                                       

Q.N.19-Muscles can efficiently synthesize glucose.                                       

Q.N.20- 131ATP molecules are produced by the complete oxidation of one molecule of Palmitic acid.                                                                                                            

 

Model Answers

Q.N.1-(Multiple Choice Questions)

1- c,  

2-d, 

3-a,  

4-b,  

5-b,  

6-b,  

7-d,  

8-b,  

9-c,   

10-b,

11-a,

12-b

13-b,

14-d,

15-d,

16-False,    

17-True,    

18-True,    

19-False,    

20-False.

 Q.N.2-a)-Salient features of Alpha helix-

1) The Alpha helix is a spiral structure.

2) The structure is stabilized by Hydrogen bonds between NH and C=O groups of the main chain.

3) Each turn is formed by 3.6 residues.

4) The distance between each amino acid residue is 1.5A.

5) It is generally right-handed.

6) In proteins like Hb and Myoglobin the alpha helix is abundant.

7) Two amino acids that disrupt the helix are proline and hydroxy proline.

Diagram and the list of participating amino acids / amino acids causing disruption of helix are to be given

b) Biochemical changes in the blood of a phenylketonuric subject- Phenyl Alanine can’t be converted to Tyrosine , it accumulates and alternate minor pathways are opened. Phenyl pyruvate, phenyl lactate and phenyl acetate accumulate in blood and are excreted in urine.

Diagnosis is made by blood phenyl Alanine levels, Guthrie test and urine ferric chloride test.

Treatment is based on early detection. The principle of treatment is to provide a diet containing low phenyl Alanine. Gene therapy is the permanent cure.

 Details of reactions are needed

c) 3 metabolic roles of glycine.

1) Formation of Haem

2) For detoxification of toxic substances

3) For the formation of bile salts.

Reactions and the clinical significance of each is needed.

Q.N.3-a) steps of de novo synthesis of fatty acids- all the steps of incorporation of acetyl co A and Malony co A to the enzyme. The steps of reduction, dehydration and reduction are to be explained. The repetition of cycles and the energy yield etc is to be explained.

b)- significance of enzyme b-hydroxy-b-methylglutaryl CoA (HMG-CoA) Reductase- it is a key regulatory enzyme of cholesterol synthesis. It is regulated by feed back inhibition, covalent modification, allosteric modification and by diet induced induction or repression. It is competitively inhibited by statins which are used for lowering plasma cholesterol levels.

 Reaction and some details are needed.

Q.N.4- a)The following compounds are toxic because

 (i) Rotenone – It inhibits the first complex of ETC, thus there is no ATP formation and death occurs due to metabolic derangements.

(ii) 2, 4-dinitrophenol- It is an uncoupler of oxidative phosphorylation

 (iii) Atractyloside- inhibits ATP/ADP translocase.

b) Alcohol consumption by an undernourished person can cause hypoglycemia- Alcohol is metabolized by alcohol dehydrogenase and aldehyde dehydrogenase, which utilize NAD+, as a result NADH accumulates and all the reactions where NAD+ is utilized are inhibited and the reactions where NADH is utilized are promoted. Hence oxaloacetate and pyruvate are converted to malate and lactate respectively limiting the substrates for Gluconeogenesis resulting in to hypoglycemia.

c) why the breath of an untreated diabetic smells of acetone- untreated diabetes mellitus leads to hyperglycemia. Non utilization of glucose leads to lipolysis. The excess acetyl co A is utilized for ketogenesis. Acetone, the Ketone body is excreted through lungs, that’s why the breath of the untreated diabetics smells of acetone.          

d) How the monitoring of glycosylated hemoglobin (HbAIc) levels is useful in the treatment of diabetes mellitus– The degree of hyperglycemia can be depicted by the conc. of glycosylated hemoglobin (HbAIc). The target of therapy is based on lowering the levels of glycosylated HbA1c . It is a better parameter than estimating blood sugar levels.

Q.N.5- Short notes on-

a) visual cycle – The steps of disintegration of Rhodopsin and reformation are to be explained.

b) One carbon metabolism- Sources and various acceptors of one carbon are to be explained. Various forms of folic acid acting as carriers of one carbon group are to be discussed.

c) Enzyme Inhibition– various types of inhibitions like competitive, non competitive, feed back, allosteric inhibition etc are to be discussed.

Q.N.6- a) Mechanism of iron absorption from the intestinal lumen- Mucosal block theory is to be explained.

b) Give an example of: (i) cyclic fatty acid – Chaulmoogric acid and hydnocarpic acid

(ii) Polyunsaturated fatty acid – Arachidonic acid

(iii) Glycolipids-Glucocerebrosides, Glucocerebrosides, Gangliosides.

c)The biochemical explanation for the presence of high levels of (i) Ketone  bodies

 The possible causes are starvation, uncontrolled diabetes mellitus, high fat feeding etc.

 (ii) Methylmalonic acid in the urine- It is excreted in the deficiency of vitamin B12. L-methyl malonyl co A is not converted to suucinyl co A, it accumulates and is thus excreted excessively in urine.                                 

 

 

                                                           

 

 

           

 

 

                                                                       

 

 

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Biochemistry- Paper-2

Date-04-11-08                                                               

Q.N.1. –a) Describe the essential differences between Metabolic Acidosis and Respiratory Acidosis.  

 b) Discuss the role of Renin -Angiotensin system in the maintenance of water and electrolyte balance of the body.

Q.N. 2. – a) What is PCR? Describe in detail the steps and applications of PCR.                                                  

b)Give a brief description of the Lac operon model of Gene expression.                                                           

Q.N.3. – a) Describe the various tests which are based on excretory functions of liver.                                     

b) Define Detoxification, Why is it required? Describe the various types of detoxification reactions occurring in the body giving one suitable example of each reaction.                                                                                                                 

Q.N.4- Write short notes on-                                                                                                                                                        

a)  Thin layer Chromatography

b) Balanced diet

c) Post translational modifications

Q.N.5 – a) What is BMR? Discuss the role of various factors that affect the BMR.                                               

b) Explain briefly the transmission and the natural course of AIDS.                                                                               

Q.N.6- Describe the followings-                                                                                                                                         

a) Characteristics of Genetic code

b) Etiology of cancers

c) Orotic aciduria

d) Sparing action

 

BIOCHEMISTRY-PAPER

(Multiple choice questions)

Date-   04-11-08-08                                                                                                                                    

Q.N.1- – The function of the Topo Isomerases is-                                          

a)  Proof reading                                                         b) Relief of super coils

c)  Polymerization                                                       d) clamp loading.

Q.N.2- Actinomycin D is an inhibitor of-                                                      

a) Replication                                                              b) Transcription

c) Translation                                                              d) all of the above.

 Q.N.3- The HIV genome can be identified by the following test:-         

a) ELISA                                                                    b) Western blot

c) PCR                                                                        d) any one of the above

 Q.N.4- In phenyl ketonurics, the phenyl acetic acid is conjugated by-    

a) Glycine                                                                 b) Acetylation

c) Glutamine                                                           d) Methylation

 Q.N.5- On the third day, following the onset of Acute Myocardial infarction which enzyme estimation will have the best predictive value?                                                                                                         

a) Serum AST                                                             b) Serum ALT

c) Serum CPK                                                             d) Serum LDH

 Q.N.6-Normal maximum Urea clearance (Cm) in an adult averages about-

a) 60                                                                            b) 65

c) 70                                                                            d) 75

 Q.N.7- The Prothrombin time in obstructive jaundice is                                

a) Normal                                                                    b) Low

c) Increases after injection of Vitamin K       d) none of the above.

 Q.N.8-   In which of the following enzymes, zinc constitutes an integral part of the enzyme-                                                                                      

a) Pepsin                                                                      b) Trypsin

c) Carbonic Anhydrase                                          d) Xanthine Oxidase  

Q.N. 9- Which of the following essential dietary factors is a precursor for a compound that acts as a “one carbon carrier”-                                                                                                                                                                               

a) Methionine                                                            b) Folic acid

c) Biotin                                                                      d) Thiamine

Q.N.10- The intake of which food stuff results in the greatest SDA-           

a) Carbohydrates                                                       b) Fats

c) Proteins                                                                   d) Calcium

Q.N.11- AFP is the most specific tumor marker for the primary carcinoma of the- 

a) Bone                                                                        b) Liver

c) Lungs                                                                      d) all of the above.                     

Q.N.12- Oxidation of which substance in the body yields the most calories per gram-

a) Glucose                                                                   b) Lipids

c) Animal protein                                                    d) Plant protein.          

Q.N.13- The synthesis of Adenylyl Cyclase is increased by-                                                  

a) Calcitonin                                                                b) Insulin

c) Parathormone                                                      d) Glucagon               

Q.N.14- RNA does not contain –                                                                                              

a) Uracil                                                                      b) Adenine

c) Thymine                                                                 d) Ribose.                    

Q.N.15- All are inhibitors of protein synthesis except-                                    

a) Tetra cyclin                                                             b) Erythromycin

c) Puromycin                                                               d) Streptoglidigin       

                                                     State true or false

Q.N.16- A given codon designates only one single specific amino acid.      

 Q.N.17-If a given Purine is changed to another Purine it is Transversion.    

 Q.N.18- The renal plasma flow is measured by the Hippuric acid test.       

 Q.N.19- Sudden increase in Gamma Glutamyl Transferase enzyme in Chronic Alcoholics signifies recent bout of drinking of Alcohol.                                                                                                                                  

 Q.N.20- The Atrial Natriuretic Peptide Hormone is synthesized in the adrenal cortex.                                                                                                                                                                                                                                                                  

                                                           Model Answers

Q.N.1- Multiple choice questions.

1)-b

2) b

3) d

4) c

5) d

6) d

7) c

8) c

9) b

10) c

11) b

12) b

13) d

14) c

15) d

16) True

17) False

18) False

19) True

20) False

 

Q.N.2-a)  The differences between Metabolic acidosis and Respiratory Acidosis- Metabolic acidosis is primary alkali deficit due to the deficiency of bicarbonate ions, While Respiratory Acidosis is due to primary carbonic acid excess. The p H and the ratio is altered in both the cases but the causes and the compensatory mechanisms and the treatment are different in both the cases. All the causes, compensatory mechanisms and the treatment are to be discussed in the tabular manner.

b) Renin – Angiotensin system- Renin is a proteoltic enzyme released from the kidney. It is released in response to the fall in sodium ion concentration, Hypovolemia, hypotension and a fall in intra cellular calcium ion conc., All these factors  stimulate the release of Renin from J.G. cells to blood. The action of Renin is mediated through the release of Angiotensin I from Angiotensinogen. Angiotensin I  is then converted to Angiotensin II and then to Angiotensin III. Both the later Angiotensins cause the release of Aldosteron from the Adrenal cortex, which causes the absorption of Sodium ions to restore the blood pressure and the fluid volume. The interdependence of Renin- Angiotensin system and the Aldosterone are  to be discussed. The clinical significance and the use of ACE inhibitors for the treatment of Hypertension are to be discussed.

Q.N.2-a)  PCR- Polymerase chain reaction is a method of amplifying a target sequence of DNA. The flanking sequences of the target DNA are required to be known. Two primers  of about 20-30 nucleotides with complementary sequence of the flanking region can be synthesized. DNA strands are separated by heating at 95 degree centigrade for 15 seconds to 2 minutes. The primers are annealed by cooling to 50 degree centigrade. The primers hybridize with their complementary single stranded DNA produced in the first step. New strands are synthesized by Taq. Polymerase. The enzyme is heat resistant , hence  it is not denatured at that high temperature. The polymerase reaction is allowed to take place for 30 seconds in the presence dNTPs. Both strands of DNA are thus duplicated. The steps are repeated, in each cycle the DNA strands are duplicated. Thus in a short span of time by simple technique the DNA  is amplified many times. In reverse PCR m RNA is detected , this allows c DNA synthesis from m RNA, followed by PCR amplification. The PCR technique is used for the diagnosis of various diseases, for medico legal cases, for the diagnosis of genetic disorders, cancer detection and also for the  Paleontological studies to study the evolution of life. The diagram showing the steps is needed.

b) Lac operon model- The synthesis of proteins under the influence of genes is called gene expression. All the genes of the cell are not expressed at all the  time. The Lac operon is an inducible catabolic operon of E.Coli. It consists of structural genes and the regulatory genes. The structural genes Z,Y and A transcribe to form a single large m-RNA with three independent translational units for the synthesis of three  distinct enzymes. The regulatory genes produce the Repressor molecule , the expression of which is constitutive. The repressor has a strong affinity for the operator which is the site between the promoter and the structural genes. When the repressor is attached to the operator the RNAP can not move further and thus the transcription of the structural genes is inhibited. So the structural genes are not transcribed. Thus when the lactose is not available, the lactose utilizing enzymes are not synthesized. When lactose is there in the medium the it binds to the repressor molecule and this complex becomes inactive and can no longer bind to the DNA. Thus the structural genes are  transcribed and the lactose is thereby utilized.

 The  Repression, De-repression of the lac operon are  to be discussed. The role of cAMP  is also to be discussed.

Q.N.3- a) Tests based on the excretory functions of the liver-  Bilirubin is formed by the catabolism of heme .It is the excretory product formed in the liver. It is conjugated in the liver to form the Bilirubin diglucuronide and excreted through bile. Measurement of Serum Biliribin, urobilinogen and stercobilinogen in blood and urine are important tests of liver functions. Besides that the BSP retention test and Indocyanin Green tests are to be discussed.

 Reactions of conjugation of Bilirubin are to be discussed with clinical significance.

 b) Detoxification- The biochemical processes whereby the toxic substances are rendered nontoxic and more water soluble are termed as detoxification. The toxicants that are lipophilic, non-polar and  are of low molecular weight are readily absorbed through the cell membranes of the skin, GI Tract and lungs and accumulate in the lipid rich areas to produce the toxic effects.  By Detoxication the substances are processed through two phases Phase I reactions are hydroxylation reactions , while phase II reactions are conjugation reactions.

 Details with  one example each are to be given for both the phases, concluding with the harmful effects of xenobiotics if they are not rendered non toxic.

 Q.N.4- a)Thin Layer Chromatography- This is another version of the liquid- liquid chromatography. A thin layer of the silica gel is spread on a glass plate, biological sample is applied as a small spot .The plate is placed in a trough containing the solvent. The stationary water phase is held on the silica gel and the mobile phase of non polar solvent moves up. In the case of TLC it takes only 3-4 hours for the separation of the substances in comparison to Paper chromatography which takes 14-16 hours, that is a distinct advantage for TLC.

Diagram, indications , merits , demerits are to be discussed.

b) Balanced Diet- A diet is said to be a balanced one when it includes proportionate quantities of food items selected from the different basic food groups so as to supply the essential nutrients in the complete fulfillment of the requirement of the body. The basic food groups and the criteria for the planning of a balanced diet are to be discussed.

c) Post Translational Modifications- The mature functional protein is formed by the post translational processes, which include the following processes-

1) Proteolytic cleavage

2) Modification of the amino acids

3) Sub unit aggregation etc. are to be discussed with suitable examples.

Q.N.5-a) BMR- The basal metabolic rate may be defined as the energy required by an awake individual during physical, emotional and digestive rest. It is the minimum amount of energy required to maintain life or sustain vital functions like the working of the heart, circulation, brain functions, respiration etc. The measurement of BMR in brief is to be discussed along with the elaboration of various factors that produce variations in BMR

 The significance of measurement is also to be discussed.

b) Transmission of HIV- The various routs like the blood, placenta ,sex etc are to me mentioned.

Natural course of the disease- Window period, seropositiveness stage and the phase of full blown AIDS are to be discussed.

Q.N.6-a) Characteristics of the Genetic code- The salient features like-

Triplet codon, non overlapping, non punctuated, degenerate, unambiguous and universal characteristics etc are to be discussed.

b) Etiology of Cancers- All cancers are multifactorial in origin. They include  genetic, hormonal, metabolic, physical, chemical and environmental factors. The effect of mutations and chemical carcinogens is also to be discussed.

c) Orotic aciduria- This condition results from the absence of either or both of the enzymes-OPRTase or OMPdecarboxylase. S/s, the lab.diagnosis and the treatment are  to be discussed.

d) Sparing action- The examples of formation of Tyrosine from phenyl Alanine and the formation of carbohydrates from the c- skeleton of amino acids is to be discussed. The relative decrease in the requirement of the phenyl Alanine and proteins is to be discussed in brief.

 

 

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