CH 5 and 6 Questions

Question 1

Which of the following would be an example of positive cooperativity?

• Binding of one oxygen to one subunit of hemoglobin facilitates the binding of other oxygen molecules to the other subunits of hemoglobin.
• Binding of one oxygen to one subunit of hemoglobin causes 2,3 Bisphosphoglycerate to bind more tightly
• Binding of one oxygen to one subunit of hemoglobin decreases the binding of other oxygen molecules to the other subunits of hemoglobin.
• Binding of one oxygen to one subunit of hemoglobin facilitates the other subunits of hemoglobin to assume the T state
• Binding of one oxygen to one subunit of hemoglobin causes the other subunits to separate from one another

Answer 1

Binding of one oxygen to one subunit of hemoglobin facilitates the binding of other oxygen molecules to the other subunits of hemoglobin.

Question 2

Which of these states of hemoglobin represents the high affinity binding O2 conformation of the hemoglobin?
  T state 
  B state 
  R state 
  D state

Answer 2

R state

Question 3

Which of the following statements about protein-ligand binding is correct?
The larger the Ka, the faster is the binding.
The Ka is independent of such conditions as salt concentration and pH.
The larger the Ka, the smaller the Kd (equilibrium dissociation constant).
The larger the Ka (association constant), the weaker the affinity.
The Ka is equal to the concentration of ligand when all of the binding sites are occupied.

Answer 3

The larger the Ka, the smaller the Kd (equilibrium dissociation constant).

Question 4

Which of the following describes the binding of 2,3 bisphosphoglycerate to hemoglobin?

• Multiple molecules 2,3 bisphosphoglycerate can bind to the same binding site.
• Binding of 2,3 bisphosphoglycerate to the hemoglobin is covalent.
• Binding of 2,3 bisphosphoglycerate to its binding site affects binding of an oxygen molecule to the same site.
• Binding of 2,3 bisphosphoglycerate allows oxygen to bind more tightly.
• Binding of 2,3 bisphosphoglycerate to its binding site affects binding properties of oxygen to other binding sites in the protein complex.

Answer 4

Binding of 2,3 bisphosphoglycerate to its binding site affects binding properties of oxygen to other binding sites in the protein complex.

Question 5

If a protein interaction with its ligand has a Hill Coefficient of 1, which of the following is true?

• The binding of one ligand molecule decreases the binding of other ligand molecules
• The protein cannot form quaternary structures
• The protein binds to other ligand molecules more readily after one ligand molecule binds
• The binding of one ligand has no effect on the binding of other ligands
• The protein ligand interaction is highly cooperative

Answer 5

The binding of one ligand has no effect on the binding of other ligands

Question 6

Which of the following statements describes the Michaelis-Menten constant Km?

• It is exactly equivalent to the Kd
• It is the substrate concentration required to reach half maximal velocity for an enzyme-catalyzed reaction.
• It is a measure of enzyme efficiency.
• It is a measure of the rate of a catalytic process.

Answer 6

It is the substrate concentration required to reach half maximal velocity for an enzyme-catalyzed reaction.

Question 7

The Vmax for an enzyme-catalyzed reaction:

• generally increases when pH increases.
• is unchanged in the presence of an uncompetitive inhibitor.
• generally increases in the presence of a competitive inhibitor.
• is twice the value of the V0 when the Km = [S].
• generally decreases as the concentration of enzyme increases.

Answer 7

is twice the value of the V0 when the Km = [S]

Question 8

In a bisubstrate reaction, substrate A binds and is then converted to product A. Next substrate B binds and is then converted to product B. Which type of reaction is described here?

• A sequential mechanism that is ordered.
• A Ping-pong mechanism that involves two enzymes.
• A Ping-pong mechanism in which no ternary complex is formed.
• A sequential mechanism that involves two enzymes.
• A sequential mechanism that is random.

Answer 8

A Ping-pong mechanism in which no ternary complex is formed.

Question 9

Which of the following statements about a plot of V0 [S] for an enzyme that follows Michaelis-Menten kinetics is false? (draw the graph as a visual aid!)

• Km is the [S] at which V0 = 1/2 Vmax.
• At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at the Km.
• The shape of the curve is a hyperbola (is hyperbolic).
• Initially as [S] increases, the initial velocity of reaction V0 also increases proportionally.
• The y-axis values are a measure of the initial velocity (rate) of a reaction.

Answer 9

At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at the Km.

Question 10

Enzymes can accelerate reactions by ________.

• Raising the energy for activation
• Positioning a metal ion to bind only to the substrate
• Binding a substrate or substrates
• Preventing the removal or addition of protons

Answer 10

Binding a substrate or substrates