Salivary amylase and starch

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Salivary amylase is a digestive enzyme secreted by the salivary glands, and about 1.7 liters of saliva is produced everyday by a healthy human. It is responsible for breakdown of the polysaccharide “starch” into dextrins (oligosaccharides), maltose (disaccharide) and glucose (monosaccharide) in the mouth.

Starch consists of two types of molecules, “amylose” (20-30%) and “amylopectin” (70-80%) and both are polymers of glucose. Amylose is a linear chain of glucose units that are linked by α-1,4 bonds, whereas amylopectin is a branched molecule in which glucose units are linked by α-1,4 bonds in the straight chain region in addition to α-1,6 bonds at the branching points. The relative proportions of amylose to amylopectin depend on the source of the starch.

Branch of amylopectin

Salivary amylase hydrolyses only the α-1,4 bonds that link glucose units. Therefore, starch and glycogen, which consist of α-1,4 bonds, are hydrolyzed by amylase while. The cellulose consisting of β-1,4 bonds, cannot be hydrolyzed by salivary amylase. The α -amylase constitute a family of endo-amylases that catalyze the initial hydrolysis of starch into shorter oligosaccharides through the cleavage of α-D-(1-4) glycosidic bonds. Neither terminal glucose residues nor α-1,6-linkages can be cleaved by α-amylase.

The conformation of (α-1→4) linkages in amylose, amylopectin causes these polymers to assume coiled helical structures. The iodine ion will be trapped in the coiled helical structures of starch and gives blue color. After digestion of starch by salivary amylase, no more helical structures available, and no color will be produced in addition of iodine. Therefore iodine can be taken as indicator to measure the activity of amylase, and sometimes, to find the inhibitor of amylase.

Nelson DDL, Cox MM (2005) Lehninger Principles of Biochemistry, 5th edition, W.H. Freeman and Co. Publisher, New York, USA, 248-252.

Model Questions for Biochemistry-II

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Model Questions for Biochemistry (Microbiology)

Long Answer Question: (5 × 5 = 25)
1) Explain the biological functions of proteins with examples.
2) Explain the essential amino acids.
3) What is the transamination process? Mention its significance.
4) What are the nucleotides? Explain the biological roles of nucleotides.
5) What are the denaturation and renaturation processes of DNA?

Multiple Choice Question: (1 × 5 = 5) (any five)
1. Marfan's syndrome is thought to be a mutation affecting
A. hemoglobin synthesis                       B. insufficient thyroid production
C. metabolism of homogentisic acid     D. collagen and/or elastin synthesis

2. Protein folding is
A. automatic, mediated by the protein itself
B. mediated by other proteins called chaperones
C. mediated by the ribosomes
D. by the protease enzyme

3. The isoelectric point of an amino acid is defined as the pH
A. where the molecule carries no electric charge
B. where the carboxyl group is uncharged
C. where the amino group is uncharged
D. of maximum electrolytic mobility

4. What is the heaviest of the twenty amino acids?
A. phenylalanine             B. tryptophan
C. tyrosine                       D. histidine

5. D-Alanine and L-Alanine are technically known as
A. polymer                       B. enantiomers
C. epimers                        D. anomers

6. Which of the following pairs of amino acids would carry a negative charge on their side chain at pH 8.0?
A. leucine & glycine              B. asparagine & glutamine
C. histidine & lysine              D. aspartate & glutamate

7. Which of the following amino acid do not fall under the category of essential amino acid?
A. leucine             B. histidine            C. glycine           D. methionine

8. What is the end product of leucine metabolism?
A. acetyl-CoA                            B. pyruvic acid
C. oxaloacetic acid                    D. acetyl carnitine

9. The nitrogen atoms of urea produced in the urea cycle are derived from
A. ammonia                                   B. ammonia and aspartic acid
C. nitrite                                         D. nitrate

10. The products of urea cycle are
A. 1 molecule of urea, 1 molecule of ammonia, 3 molecules of GTP and 1 molecule of fumaric acid
B. 1 molecule of fumaric acid, 1 molecule of urea, 1 molecule of AMP, 2 molecules of ADP
C. 1 molecule of aspartic acid, 1 molecule of ammonia, 1 molecule of fumaric acid, 1 molecule of ATP
D. 1 molecule of urea, 1 molecule of ammonia, 1 molecule of ATP and 1 molecule of fumaric acid

11. Which of the following is used as carbon atom source while producing urea in the urea cycle?
A. arginine                                         B. aspartic acid
C. carbon dioxide                               D. glucose

12. Urea cycle converts
A. ammonia into a less toxic form
B. urea into nitrogen
C. amino acids into ketoacids
D. ketoacids into amino acids

13. The inputs to one cycle of the urea cycle are
A. 1 molecule of aspartic acid, 1 molecule of ammonia, 1 molecule of carbon dioxide, 3 molecules of ATP
B. 1 molecule of urea, 1 molecule of ammonia, 3 molecules of ATP and 1 molecule of fumaric acid
C. 1 molecule of fumaric acid, 1 molecule of urea, 3 molecules of AMP
D. 1 molecule of acetic acid, 1 molecule of urea, 3 molecules of GTP

Model Questions for Biochemistry

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Model Questions for Biochemistry (Biotechnology)

Long Answer Question: (6 × 1 = 6) (any one)
1) Explain the biological functions of proteins with examples.
2) Explain the essential amino acids.

Short Answer Question: (2.5 × 2 = 5) (any two)
1) Describe how peptide bond is formed.
2) Draw the structures of non-polar and non-charged aliphatic amino acids.
3) Mention the the enzymes and co-factors involved in hydroxylation of proline and lysine in collagen synthesis.

Very Short Answer Question: (1 × 4 = 4) (any four)
1) Define denaturation of proteins.
2) Which bonds are flexible for rotation in a dipeptide?
3) Mention the replaced amino acids that leads to sickle cell anemia.
4) Define the quaternary structure of proteins?
5) What are the major amino acids in collagen?
6) What is the Ramachandran Plot?

Multiple Choice Question: (1 × 5 = 5) (any five)

1. Marfan's syndrome is thought to be a mutation affecting
A. hemoglobin synthesis                       B. insufficient thyroid production
C. metabolism of homogentisic acid     D. collagen and/or elastin synthesis

2. Protein folding is
A. automatic, mediated by the protein itself
B. mediated by other proteins called chaperones
C. mediated by the ribosomes
D. by the protease enzyme

3. The isoelectric point of an amino acid is defined as the pH
A. where the molecule carries no electric charge
B. where the carboxyl group is uncharged
C. where the amino group is uncharged
D. of maximum electrolytic mobility

4. What is the heaviest of the twenty amino acids?
A. phenylalanine             B. tryptophan
C. tyrosine                       D. histidine

5. D-Alanine and L-Alanine are technically known as
A. polymer                       B. enantiomers
C. epimers                        D. anomers

6. Which of the following pairs of amino acids would carry a negative charge on their side chain at pH 8.0?
A. leucine & glycine              B. asparagine & glutamine
C. histidine & lysine              D. aspartate & glutamate

7. Which of the following amino acid do not fall under the category of essential amino acid?
A. leucine             B. histidine            C. glycine           D. methionine

Qualitative Detection of Glucose in Urine

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Glucose is not present in urine, in general because in the kidneys, glucose is reabsorbed from the filtrate of glomerulus, across the tubular epithelium of proximal tubule into the bloodstream. Therefore, normal glucose range in urine is 0 mg/dL, or rarely up to 15 mg/dL. If higher than normal levels of glucose (0-15 mg/dL) is found in urine, then it can be suspected as diabetes, pregnancy, or renal glycosuria. Presence of glucose in urine was commonly tested to monitor diabetes in the past. Now, blood tests for glucose is easier than urine test. The glucose urine test may be done when there is suspect of renal glycosuria.

One of the test is based on the basis of character of glucose as it is a reducing carbohydrate because of a free aldehyde group. During the reduction process of Cu(OH)₂ to CuOH by the glucose aldehyde group, and itself is converted into a carboxyl group. CuOH and its degradation product, Cu₂O, are colored compounds. In excess of CuSO₄, the high Cu(OH)₂ content may lead to the formation of black CuO particles. This is called Trommer’s reaction and explained in the following equations;

Trommer's Explannation

Karl Trommer (1806-1879), German chemist first developed this copper reduction test in 1841, and more stable copper sulphate reagent was explained by Hermann von Fehling (1812-1885) in 1850. Even more sensitive copper reagent was described in 1908 by Stanley Benedict (1884-1936). Later, Ames (1945), the research team led by Albert & Helen Free, developed Clinitest tablet, which contained cupric sulfate, sodium hydroxide, and citric acid mixed with a bit of carbonate to make it fizz. Helen M. Free (1923-) and Alfred Free (1913–2000), revolutionized diagnostic urine testing with their invention of a chemically coated paper dipstick that measures a patient’s blood/urine sugar by changing color when dipped in a blood/urine sample.