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1. What are the components of PDH(Pyruvate dehydrogenase) complex?



a) Pyruvate dehydrogenase

b) Dihydro lipoyl transacetylase

c) Dihydrolipoyl dehydrogenase

d) PDH kinase

e) Phosphatase

Coenzymes- Thiamine pyro phosphate (TPP), Co ASH, Lipoic acid, FAD and NAD+

2- What is the biological role of Oxalo acetate?

Answer- Oxalo acetate is required for the functioning of TCA cycle; for the synthesis of glucose ; for the synthesis of Aspartate and Asparagine.

3- What is the fate of pyruvate under different conditions?

Answer- The main fate is conversion to Acetyl co A. Depending upon cellular needs and the availability of oxygen it can be converted to lactate, alanine, oxalo acetate, malate or ethanol (in micro organisms).

4- What is Pasteur Effect?

Answer- The inhibition of glycolysis upon oxygen administration when the glucose was previously getting oxidized under anaerobic condition is called Pasteur Effect.

Biochemical basis-Glycolysis occurs at a higher rate during anaerobic conditions. Hypoxia stimulates glycolysis. Upon oxygen administration, the conditions change from anaerobic to aerobic, there is more ATP formation. ATP is a negative allosteric modifier of PFK-1, the key regulatory enzyme of glycolysis. Inhibition of PFK-1 causes inhibition of glycolysis.

5- In which of the organs of the body, maximum amount of glycogen is stored?

Answer- Glycogen occurs mainly in liver and muscle; although the liver content of glycogen is greater than that of muscle, because the muscle mass of the body is considerably greater than that of the liver, about three-quarters of total body glycogen is in muscle

6- Name the key regulatory enzyme of glycolysis?

Answer- Phospho-fructo kinase-1 (PFK-1) is the key regulatory enzyme of glycolysis.

6- Which pathway is maximally active in the fed state (Glycogenesis /glycogenolysis)?

Answer- Glycogenesis occurs maximally in the fed state under the effect of insulin.

7- What is the biochemical defect in hereditary fructose intolerance?

Answer- Deficiency of Aldolase B enzyme

8- Why is it inappropriate to say that “Fats can not be converted to glucose?”

Answer- Glycerol and odd chain fatty acids are glucogenic. It is only Acetyl co A , the product of oxidation of even chain fatty acids that  is not glucogenic. Thus it is not appropriate to say that fats can not be converted to glucose.

9-Out of Glucokinase and hexokinase which of the enzymes is inducible in nature?

Answer- Glucokinase is inducible in nature.

10- Which type of the glucose transporters are under the control of insulin?

Answer-Only GLUT-4 transporters, present in skeletal muscle and adipose tissue are insulin dependent.

11- Enumerate the sources of NADPH.

Answer- NADPH can be produced from-

a) HMP shunt pathway

b) By the activity of cytosolic isocitrate dehydrogenase and

c) By the activity of Malic enzyme.

12- Which reaction is catalyzed by Glucose-6-P dehydrogenase?

Answer- Glucose-6-P dehydrogenase catalyzes the conversion of glucose-6-P to 6-Phosphogluconolactone.

13- What is the effect of rising concentration of AMP on glycolysis?

Answer- Rising concentration of AMP is a sign of low energy state of the cell. AMP acts as a positive allosteric modifier for PFK-1 enzyme. The enzyme gets stimulated to activate the pathway.

14- What is the effect of rising concentration of citrate on PFK-1?

Answer- Citrate is a negative allosteric modifier of PFK-1. Reduced activity of PFK-1 in the presence of high concentration of citrate results in inhibition of glycolytic pathway

15- Which reaction is catalyzed by lactate dehydrogenase enzyme?

Answer- Lactate dehydrogenase causes interconversion of pyruvate and lactate.

16- Name the pathways of glucose utilization in red blood cells?

Answer- Glucose is utilized through glycolysis and HMP pathway in red blood cells.

17- What is the cause of positive Benedict’s test in essential Pentosuria?

Answer- Excess excretion of L- Xylulose, which is reducing in nature, gives a positive reaction with Benedict’s reagent in essential Pentosuria.

18- Out of Transaldolase and transketolase which of these two enzymes is TPP dependent?

Answer- Transketolase, an enzyme of HMP pathway is TPP dependent.

19- Name the coenzymes needed for the functioning of Alpha keto glutarate dehydrogenase complex?

Answer- The coenzymes are same as PDH complex, and these are -Thiamine pyro phosphate (TPP), Co ASH, Lipoic acid, FAD and NAD+.

20- What is the cause of premature cataract in classical galactosemia?

Answer- In classical galactosemia,  excess of unutized galactose is reduced to galacitol which is osmotically  active to cause opacification of lens to cause cataract.



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