- # About the Author
- # About the web site
- # Our second web site
- # Question of the day
- A New Book of Biochemistry
- Acid Base Balance
- Animations Links
- Biochemical Techniques
- Biochemistry Quiz
- Biological Oxidation
- Chemistry of Carbohydrates
- Chemistry of Lipids and Eicosanoids
- Chemistry of Nucleotides
- Chemistry of Proteins
- Diabetes Mellitus
- Diet and Nutrition
- Facebook Group Posts
- Haem Synthesis and Degradation
- Hemoglobin and Hemoglobinopathies
- Liver Function Tests
- Metabolism – Carbohydrates
- Metabolism – Lipids
- Metabolism – Nucleotides
- Metabolism – Proteins
- Metabolism of Alcohol
- Molecular Biology
- Past Papers
- Power Point Presentations
- Practical Biochemistry
- Abnormal Urine
- Blood Glucose Estimation
- Blood Urea and Urea Clearance Estimation
- Normal Laboratory Reference Values
- Normal Urine Analysis
- Power point presentations
- Protein Precipitation Reactions
- Reactions of Carbohydrates
- Serum Creatinine and Creatinine clearance estimation
- Serum Total Protein estimation
- Practice Questions
- Quick revisions
- Renal Function Tests
- Semester Paper
- Students’ corner
- Water and Electrolyte balance and Imbalance
Reaction catalyzed by Amylase
A. α- 1, 4
B. α- 1, 6
C. β-1, 4
D. α 1, 2
E. β-1, 6
Answer- A) alpha – 1, 4 is the right answer.
Amylase acts on starch and glycogen to cleave α- 1, 4 glycosidic linkages.
Dietary polysaccharides (starch and glycogen) are digested first by salivary amylase to form dextrins that are further shortened by pancreatic amylase to form maltose. Maltose is further digested by maltase to form two glucose residues (figure-1).
Both starch and glycogen are polymers of glucose. The two main constituents of starch are amylose (13–20%), which has a nonbranching helical structure, and amylopectin (80–85%), which consists of branched chains composed of 24–30 glucose residues united by α-1,4 linkages in the chains and by α-1 ,6 linkages at the branch points (figure-2).
Glycogen, a more highly branched structure than amylopectin contains chains of 12–14 α-D-glucopyranose residues (in α-1, 4 glucosidic linkage) with branching by means of α-1, 6 glucosidic bonds (figure-2).
Amylase acts on alpha – 1, 4 glycosidic linkages only, the branch point containing α- 1, 6 linkage cannot be cleaved by amylase. Both starch and glycogen are substrates for amylase, having the structural similarities.
Figure-1- An overview of digestion of carbohydrates. Salivary digestion is limited due to shorter duration of stay of food in the oral cavity. The polysaccharides are mainly digested by Amylases (salivary and pancreatic, that are isoenzymes, they catalyze the same reaction, but differ from each other in their physical properties)
As regards other options
Cellulose a polymer of glucose 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 (figure-3).
α 1,2 linkage, more precisely- O-α-D-glucopyranosyl-(1,2)-β -D-fructofuranoside linkage is found in sucrose that is hydrolyzed by sucrase.
Β-1, 6 linkages are not common in nutrients.
Figure-2- Structure of Amylose, amylopectin and glycogen. Amylopectin and glycogen are structurally alike, except for the fact that glycogen is more branched than amylopectin. Both components of starch and glycogen contain alpha 1, 4 glycosidic linkages, hence they are ideal substrates for Amylase.
Figure-3- Comparison of structures of starch, glycogen and cellulose. Starch and glycogen are similar structurally whereas cellulose, despite being a polymer of glucose cannot be digested by human beings as it contains beta 1, 4 glycosidic linkages. Cellulose is digested by Cellulase enzyme.
Please help "Biochemistry for Medics" by CLICKING ON THE ADVERTISEMENTS above!