OBJECTIVES
1. Pepsin is secreted as an inactive precursor called pepsinogen because
A. pepsin as an enzyme is quickly destroyed by the alkaline food from the mouth.
B. all digestive enzymes pass through a precursor stage.
C. pepsin is a proteolytic enzyme and might attack the stomach tissues.
D. pepsin is not required in large quantities.
2. Adenine pairs with thymine because
A. the two occur in the same nucleic acid.
B. one is a strong base and the other a weak base.
C. two purine bases easily pair up.
D. one is a purine base and the other a pyrimidine.
3. Which of the following digestive enzymes would be greatly affected if the liver fails to produce bile?
A. Amylase,
B. Cellulase.
C. Lipase.
D. Protease.
4. The name of the enzyme that catalyzes the conversion of glucose to glucose-6-phosphate at the beginning of glycolysis is
A. phosphofructokinase.
B. glucose-isonterase.
C. hexokinase.
D. glucose-6-kinase.
5. Enzymes can be inactivated by certain chemical substances in the body called
A. catalysts.
B. inhibitors.
C. substrates.
D. activators.
6. Which of the following enzymes is not one of the main classes of enzymes?
A. Sucrase.
B. Amylases.
C. Proteases.
D. Lipases.
7. Which of the following food substances is incorrectly linked to its enzyme?
A. Protein-trypsin.
B. Fat-lipase.
C. Sucrose pepsin.
D. Starch-amylase.
8. Which of the following enzymes does not belong to proteases?
A. Sucrase.
B. Pepsin
C. Trypsin.
D. Erepsin.
9. Which of the following pH values is the best for the action of the enzymes – renin and pepsin in the
stomach?
A. pH 2.
B. pH 7.
C. pH 8.
D. pH 9.
10. Which of the following enzymes is active in the duodenum?
A. Pepsin.
B. Renin.
C. Trypsin.
D. Amylase.
11. Which of the following juices contains the enzyme ptyalin
A. Gastric juice.
B. Pancreatic juice.
C. Succus.
D. Saliva.
12. If an enzyme works best in an acid medium, in which of the following parts of the human gut is the pH best for enzyme activities? In the
A. ileum, pH 9.0.
B. stomach, pH 2.0.
C. duodenum, pH 7.0.
D. mouth cavity; pH 8.0.
13. The enzyme that acts on milk in the stomach is
A. invertase.
B. trypsin.
C. diastase.
D. renin.
14. Which of the following statements is true?
A. Ptyalin acts on proteins to give amino acid.
B. Lactase acts on maltose to give amino acid.
C. Pepsin acts on proteins to give peptide.
D. Peptide acts on starch to give maltose.
15. Which of the following statements about a mixture of a protein-digesting enzyme and starch solution would be correct? The protein-digesting enzyme
A. Has no effect on the starch solution.
B. Leads to the production of amino acids.
C. Leads to the production of glucose.
D. Digests the starch.
16. An enzyme reaction may begin to decline when
A. the optimum temperature is attained.
B. the pH of the medium is altered.
C. there is an increase in substrate concentration.
D. the atmospheric pressure is altered.
Diagram J is a protease while diagrams K, L, M and N are food substances. Study them and answer questions 17 to 19.
17. Which of the illustrated food substances would form a reaction with protease J?
A. K
B. L
C. M
D. N
18. Protease J would react with the particular illustrated substance because enzymes
A. are denatured at a high frequency.
B. are specific in their action.
C. remain unchanged after a reaction.
D. speed up the rate of chemical reaction.
19. After a reaction between protease J and the food substance, the end-product would be
A. fatty acids.
B. glucose.
C. amino acids.
D. water.
THEORY
1. In a tabular form, state the source, substrate and end products of the following enzymes (i) ptyalin; (ii) pepsin; (iii) lipase.
2 (a) State four characteristics of enzymes (b)List two examples of digestive enzymes produced in the duodenum of humans; (c) Name the substrate for each enzyme listed in (b); (d) State the products of each enzyme activity in (b) above.
3. (a) State three characteristics of enzymes (b) In a tabular form indicate the source, substrate acted upon and the product of the following enzymes: ptyalin, pepsin.
4. (a) Name one organelle in a living cell that produces enzyme (b) Mention two enzymes that act on proteins.
5. (a) Define enzymes (b) State six characteristics of enzymes.