Homework 5

Question 1

Which amino acid would most likely participate in general acid-base catalysis under basic conditions?

Gln

Ala

Leu

Tyr

Answer 1

Tyr

Question 2

Which of the following mechanisms can affect enzymatic activity?

substrate availability

covalent modification

cleavage of a zymogen

all of the above

Answer 2

All of the above

Question 3

Which of the following statements is FALSE about allosteric enzymes?

The regulators associated with them bind only to the active site.

They are most active in the relaxed (R) form.

They produce a sigmoidal curve.

They work quickly and are direct.

Answer 3

The regulators associated with them bind only to the active site.

Question 4

Which one of the following mechanisms is NOT known to play a role in the reversible alteration of enzyme activity?

Covalent modification of the enzyme.

Allosteric response to a regulatory molecule.

Alteration of the synthesis or degradation rate of an enzyme.

Activation by cleavage of an inactive zymogen.

Interactions between catalytic and regulatory subunits.

Answer 4

Activation by cleavage of an inactive zymogen. ( activation of enzyme by proteolytic cleavage is irreversible).

Question 5

Which of the following statements regarding allosteric enzymes is true?

They are always oligomeric.

They are generally found at regulatory sites in metabolic pathways.

They are subject to regulation by both positive and negative effectors.

A plot of velocity versus [substrate] often yields a sigmoidal curve.

All of the above

Answer 5

All of the above

Question 6

This chapter discusses the regulation of proteins by allostery, phosphorylation, or proteolytic cleavage. Of these, which is irreversible? Which occurs most quickly? Which is the most specific?

1. Which is irreversible?
2. Which type of regulation occurs most quickly?
3. Which type of regulation is the most specific?
4. Which type of regulation has broad specificity and is reversible?

Answer 6

1. Proteolytic cleavage
2. Allostery
3. Allostery
4. Phosphorylation

Question 7

The Lineweaver-Burk plot is also known as the double-_______________ plot.

Answer 7

Reciprocal

Question 8

Allosterism

means “other shape”

is induced by binding of another molecule to a protein

is important to protein regulation

leads to change in conformation and activity

All of the above

Answer 8

All of the above

Question 9

Proteins/enzymes that can be regulated allosterically
I. show a hyperbolic Michaelis-Menten curve
II. can be regulated by molecules that differ structurally from a substrate
III. can be both activated and inhibited
IV. undergo only competitive inhibition

I and II

I, III and IV

II and III

I, II, III and IV

I, II and III

Answer 9

II and III

Question 10

Enzymes that are allosterically regulated

A) show an activity vs. substrate concentration curve that is sigmoidal

B) may be stimulated by allosteric activators

C) when inhibited show an activity curve shifted to the right

D) Both A and B

E) All of the above

Answer 10

E) All of the above