Mechanism of enzyme action. Regulation of enzyme activity

Choose the one correct answer:

1. The active center of enzyme:

A. is the region of the enzyme where substrate binding and catalysis;

B. is the region of the enzyme where substrate binding;

C. is the region of the enzyme where substrate catalysis;

D. is the region of the enzyme where activator binding;

E. is the region of the enzyme where inhibitor binding.

2. What is the activation energy?

A. the energy required to convert first molecule of reacting substance from the ground state to the transition state;

B. the energy required to convert 50% molecules of reacting substance from the ground state to the transition state;

C. the energy required to convert all molecules in one mole of reacting substance from the ground state to the transition state;

D. the energy required to convert 50% molecules of reacting substance from the transition state to the product reaction;

E. the energy required to convert all molecules in one mole of reacting substance from the transition state to the product reaction;

3. Which one of the following statements about Km is correct?

A. it shows the relationship between the temperature and the enzymatic reaction rate:

B. it shows the relationship between the pH and the enzymatic reaction rate;

C. it shows the relationship between the substrate or enzyme concentration and the enzymatic reaction rate;

D. it shows the relationship between the substrate concentration and the enzymatic reaction rate;

E. it shows the relationship between the enzyme concentration and the enzymatic reaction rate.

4. What type activation characterized for zymogens?

A. reversible covalent modification;

B. reversible competitive activation

C. allosteric modulation;

D. irreversible non-covalent activation;

E. irreversible covalent activation.

5. Which one of the following statements about allosteric inhibition is correct?

A. the inhibitor is a substrate analog;

B. it is irreversible;

C. the Km is usually decreased;

D. when an inhibitor binds to the allosteric site, the configuration of catalytic site is not modified, so the substrate can bind property;

E. when an inhibitor binds to the allosteric site, the configuration of catalytic site is modified such the substrate cannot bind property.

6. A competitive inhibitor of an enzyme:

A. Increases Km without affecting V max

B. Decreases Km without affecting V max

C. Increases V max without affecting Km

D. Decreases V max without affecting Km

E. Decreases both V max and Km

7. The Michaelis constant, Km is:

A. numerically equal to V max;

B. dependent of pH;

C. independent of pH;

D. numerically equal to the substrate concentration that gives half-maximal enzymatic reaction rate;

E. increased in the presence of a noncompetitive inhibitor.

8. Which one of the following pairs is incorrect?

A. The rate/velocity of a reaction	is the number of substrate molecules converted to product per unit time /µmol of product formed per minute
B. Increase of rate/velocity with temperature	until a peak velocity is reached
C. Increase of rate/velocity with temperature	is the result of the increased number of molecules having sufficient energy to pass over the energy barrier and form the products of the reaction
D. Decrease of rate/velocity with higher temperature	Further elevation of the temperature results in a decrease in reaction velocity as a result of temperature-induced denaturation of the enzyme.
E. Decrease of rate/velocity with higher temperature	Further elevation of the temperature results in a decrease in reaction velocity as a result of temperature-induced denaturation of the cofactors.

9. Which one of the following factors affecting reaction rate is incorrect?

A. substrate concentration;

B. enzyme concentration;

C. temperature;

D. pH;

E. constant temperature.

10.Lactate dehygpogenase catalyses the reversible interconversion of lactate and pyruvate. It is widely distributed with high concentrations in the following tissues. Choose one incorrect answer.

A. in the adipose tissue and brain;

B. in the heart and kidney;

C. in the muscle and liver;

D. in the brain and erythrocytes;

E. in the heart and erythrocytes.