This set of Class 11 Biology Chapter 9 Multiple Choice Questions & Answers (MCQs) focuses on “Biomolecules – Enzymes and Biocatalysts-2”.
1. The energy of the transition state of an enzymatic reaction is _____
a) higher than the energy of the product but lesser than that of the substrate
b) lower than the energy of the product
c) equal to the energy of the substrate
d) higher than the energies of both the substrate and the product
View Answer
Explanation: The transition state occurs during an enzymatic reaction when the substrate binds to the enzyme molecule in order to be converted into a product. The energy of this state is higher than that of the substrate and the product.
2. Which of these statements is false regarding transition states in enzymatic reactions?
a) They are more unstable than products
b) They have high energy
c) They have a lower energy than both substrate and product
d) An enzyme-substrate complex is formed during this period
View Answer
Explanation: The transition state occurs during an enzymatic reaction when the substrate binds to the enzyme molecule in order to be converted into a product, via the production of a high energy enzyme-substrate complex.
3. Which of these conditions signify an exothermic reaction?
a) The energy of the product is lesser than that of the enzyme-substrate complex
b) The energy of the product is higher than that of the substrate
c) The energy of the product is lesser than that of the substrate
d) The energy of the product is equal to that of the substrate
View Answer
Explanation: In an enzymatic reaction, a substrate is converted into a product via the formation of a higher energy enzyme-substrate complex. If the energy of the product is lesser than that of the substrate, it signifies an exothermic reaction.
4. Which of these is the second step of an enzymatic reaction?
a) Binding of the substrate to the enzyme
b) Change in the conformation of the enzyme
c) Production of an enzyme-substrate complex
d) Release of product from the enzyme
View Answer
Explanation: In an enzymatic reaction, a substrate first binds to the active site of an enzyme. This induces a conformational change in the enzyme to form an enzyme-substrate complex. This is converted into a product which is then released.
5. Which of these is the third step of an enzymatic reaction?
a) Binding of the substrate to the enzyme
b) Change in the conformation of the enzyme
c) Production of an enzyme-substrate complex
d) Release of product from the enzyme
View Answer
Explanation: In an enzymatic reaction, a substrate first binds to the active site of an enzyme. This induces a conformational change in the enzyme to form an enzyme-substrate complex. This is converted into a product which is then released.
6. Which of these substances is structurally similar to succinate?
a) Pyruvate
b) Acetate
c) Malonate
d) Oxaloacetate
View Answer
Explanation: Malonate is structurally similar to succinate. Malonate acts as a competitive inhibitor for the substrate succinate. Binding of malonate instead of succinate inhibits the activity of the enzyme succinic dehydrogenase.
7. How many classes are enzymes divided into?
a) 6
b) 7
c) 5
d) 8
View Answer
Explanation: Enzymes are divided into 6 classes based on the type of reactions they catalyze. The six classes of enzymes are as follows-oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases.
8. Nicotinamide adenine dinucleotide is a _____
a) cofactor
b) prosthetic group
c) apoenzyme
d) coenzyme
View Answer
Explanation: Nicotinamide adenine dinucleotide (NAD) is a coenzyme. It is an organic compound that transiently associates with an apoenzyme during the process of catalysis. It contains the vitamin niacin.
9. What does the graph represent?
a) Effect of change in pH on enzyme activity
b) Effect of change in temperature on enzyme activity
c) Effect of change in concentration of substrate on enzyme activity
d) Effect of change in pressure on enzyme activity
View Answer
Explanation: The graph given above represents the effect of change in concentration of substrate on enzyme activity. Velocity of the reaction increases with an increase in substrate concentration at first, but it ultimately reaches a maximum velocity.
10. Velocity of an enzymatic reaction keeps on increasing with an increase in substrate concentration. True or false?
a) True
b) False
View Answer
Explanation: Velocity of an enzymatic reaction increases with an increase in substrate concentration at first, but it ultimately reaches a maximum velocity. This is due to the saturation of substrate molecules.
11. Which of these statements is true regarding competitive inhibitors?
a) It inhibits the activity of substrate
b) Malonate increases succinic dehydrogenase activity
c) They are structurally different from the substrate
d) They are used in the control of bacterial pathogens
View Answer
Explanation: Competitive inhibitors inhibits the activity of enzymes. They are structurally similar to the substrate. Malonate is a competitive inhibitor for succinic dehydrogenase. They are used to control pathogens.
12. What type of enzyme catalyzes the conversion of d-lactic acid to l-lactic acid?
a) Oxidoreductases
b) Transferases
c) Isomerases
d) Ligases
View Answer
Explanation: D-lactic acid and l-lactic acid are optical isomers. They can be interconverted into either form with the help of isomerases. These enzymes catalyze the interconversion of optical, positional and geometric isomers.
13. Which of these is the cofactor for carboxypeptidase?
a) Manganese
b) Magnesium
c) Zinc
d) Copper
View Answer
Explanation: Carboxypeptidase is a proteolytic enzyme. It functions with the help of a metal ion, zinc, working as the cofactor. Zinc forms one or more coordinate bonds with the enzyme as well as with the substrate.
14. The association of which of these with apoenzymes is transient?
a) Coenzyme
b) Prosthetic group
c) Metal enzyme
d) Apoenzyme
View Answer
Explanation: Coenzymes are organic compounds. The associations of coenzymes and apoenzymes are transient and occur during catalysis. Vitamins are important chemical components of coenzymes.
15. What is the heme portion of catalase known as?
a) Coenzyme
b) Prosthetic group
c) Metal enzyme
d) Apoenzyme
View Answer
Explanation: Heme is a prosthetic group of the catalase enzyme. It is an organic compound which is bound tightly to the apoenzyme. The prosthetic group is present at the active site of the catalase enzyme.
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