Question

1. State whether the following statements are true or false.

i) An enzyme catalyst DOES alter the equilibrium constant for a reaction.

ii) The presence of an enzyme catalyst DOES NOT decrease the energy required to reach the transition state.

iii) An enzyme catalyst DOES affect the rate of a biochemical reaction.

iv) The presence of an enzyme catalyst DOES NOT decrease the change in free energy (Gfinal - Ginitial) of the overall reaction.

2. True or False?
Due to transition state stabilization, the enzyme proline racemase would be predicted to bind to an intermediate with a tetrahedral carbon at the reaction site rather than a trigonal planar carbon.

3. An enzyme is found to produce -OH as a nucleophile from water during the mechanism of the catalyzed reaction. Which would NOT be a good candidate in the enzyme for the molecule primarily responsible for the formation of this -OH?

A) a deprotonated Ser in the active site

B) Zn2+

C) a deprotonated His in the active site

D) a Val in the active site

4. What is the best description of the "oxyanion hole" generated during the mechanism of a serine protease - catalyzed reaction?

A) the oxyanion hole describes the stabilization of the tetrahedral intermediate where H-bonding lowers the energy of the negatively charged oxygen resulting from nucleophilic attack on the carbonyl carbon

B) the oxyanion hole describes the planar enzyme-substrate intermediate formed as the carbonyl double-bond is reformed.

C) the oxyanion hole is generated as a result of deprotonation of the serine by a neighboring histidine, resulting in a negatively charged oxygen nucleophile

D) the oxyanion hole describes the binding pocket for the phenylalanine amino acids that are preferred substrates for the serine proteases

5. Which statement describes a common feature of both the RNase A and Serine Protease mechanisms?

A) Water is protonated by a Histidine to generate an acidic hydronium ion.

B) A deprotonated serine acts as a nucleophile

C) a covalent enzyme-substrate intermediate is formed

D) a Histidine acts as a Bronsted base to remove a proton from an alcohol group.

Answer 1

Answer 1)

i) An enzyme catalyst DOES alter the equilibrium constant for a reaction. True

ii) The presence of an enzyme catalyst DOES NOT decrease the energy required to reach the transition state. False

iii) An enzyme catalyst DOES affect the rate of a biochemical reaction. True

iv) The presence of an enzyme catalyst DOES NOT decrease the change in free energy (Gfinal - Ginitial) of the overall reaction. False

ANSWER 2)

Due to transition state stabilization, the enzyme proline racemase would be predicted to bind to an intermediate with a tetrahedral carbon at the reaction site rather than a trigonal planar carbon. False

Answer 3)

Zn+2

Answer 4)

the oxyanion hole describes the stabilization of the tetrahedral intermediate where H-bonding lowers the energy of the negatively charged oxygen resulting from a nucleophilic attack on the carbonyl carbon.

Answer 5)

Water is protonated by a Histidine to generate an acidic hydronium ion.