Enzymes - Nature and Mechanism - UNSOLVED PRACTICE SET
Chapter: Biomolecules | Topic: Enzymes Nature and Mechanism
ENZYMES - NATURE AND MECHANISM - UNSOLVED PRACTICE SET
Topic: Enzymes Nature and Mechanism
Multiple Choice Questions
Q1. Enzymes are:
- Carbohydrates
- Proteins
- Lipids
- Nucleic acids
Q2. The region of an enzyme where the substrate binds is called:
- Active site
- Allosteric site
- Binding site
- Catalytic site
Q3. The lock and key model of enzyme action was proposed by:
- Koshland
- Fischer
- Michaelis
- Menten
Q4. According to the induced fit model:
- The enzyme and substrate are rigid and do not change shape
- The enzyme changes its shape to fit the substrate
- The substrate changes its shape to fit the enzyme
- Both enzyme and substrate change shape to fit each other
Q5. The optimum pH for the enzyme pepsin is:
- 2
- 7
- 8
- 10
Q6. Competitive inhibition of an enzyme occurs when the inhibitor:
- Binds to the allosteric site
- Binds to the active site
- Destroys the enzyme
- Binds to the substrate
Short Answer Questions
Q7. What are enzymes? Why are they called biocatalysts?
Q8. Distinguish between the lock and key model and the induced fit model of enzyme action.
Q9. What is the active site of an enzyme? Name the two regions within the active site and their functions.
Q10. Why does enzyme activity decrease at very high temperatures? Explain in terms of protein structure.
Q11. What is enzyme inhibition? Distinguish between competitive and non-competitive inhibition.
Q12. When you have a fever, you often lose your appetite. Explain this observation in terms of enzyme activity and body temperature.
Long Answer Questions
Q13. (a) What are enzymes? Describe their characteristics.
(b) Explain the mechanism of enzyme action according to:
(i) The lock and key model
(ii) The induced fit model
(c) Why is the induced fit model considered more accurate than the lock and key model?
Q14. (a) Explain the factors that affect enzyme activity:
(i) Temperature
(ii) pH
(iii) Substrate concentration
(iv) Enzyme concentration
(b) Draw a rough sketch showing how enzyme activity varies with temperature. Label the optimum temperature and explain what happens below and above this temperature.
Q15. (a) What is enzyme inhibition? Describe the following types with examples:
(i) Competitive inhibition
(ii) Non-competitive inhibition
(iii) Allosteric inhibition
(b) How can competitive inhibition be overcome? Why is this not possible with non-competitive inhibition?
Numerical / Application-Based Problems
Q16. An enzyme-catalyzed reaction follows Michaelis-Menten kinetics. The following data was obtained:
| [S] (mM) | Rate (ฮผmol/min) |
|---|---|
| 0.5 | 20 |
| 1.0 | 33 |
| 2.0 | 50 |
| 4.0 | 67 |
| 8.0 | 80 |
| 16.0 | 89 |
(a) Plot a rough graph of rate vs. [S] and estimate Vmax from the graph.
(b) Estimate Km (the substrate concentration at which rate = Vmax/2).
(c) What does Km tell you about the affinity of the enzyme for its substrate?
(d) If a competitive inhibitor is added, how would Vmax and Km change?
(e) If a non-competitive inhibitor is added, how would Vmax and Km change?
Q17. The enzyme amylase catalyzes the hydrolysis of starch to maltose.
(a) Where in the human body is amylase found? Name the two locations.
(b) The optimum pH for salivary amylase is 6.8, while for pancreatic amylase it is 7.0. Why is there a slight difference?
(c) A student chews a piece of bread for 5 minutes without swallowing. The bread begins to taste sweet. Explain the biochemical reaction responsible.
(d) If the student drinks a very acidic soft drink (pH 2) immediately after chewing bread, what happens to the amylase activity? Why?
(e) Some people lack the enzyme lactase and cannot digest lactose. What condition does this cause? How can such people consume dairy products?
Q18. In a school biology experiment, students study the enzyme catalase, which breaks down hydrogen peroxide:
2HโOโ โ 2HโO + Oโ
(a) Where is catalase found in the human body? Why is it important?
(b) The students add a piece of raw potato (rich in catalase) to hydrogen peroxide solution and observe vigorous bubbling. Write the reaction and identify the gas evolved.
(c) When the potato is boiled before adding to HโOโ, no bubbling is observed. Explain why, mentioning the level(s) of protein structure affected.
(d) The students add copper sulphate solution to the reaction mixture. The bubbling slows down. What type of inhibition is this? Explain the mechanism.
(e) The students then add more hydrogen peroxide to the inhibited mixture. The bubbling does not resume. What does this tell you about the nature of the inhibition?