MCAT: Biochemistry Review
(Freestanding Practice Questions And
Answers | Verified
Which of the following best describes the function of enzymes?
A) By decreasing the Ea, enzymes increase both the reaction rate and the total amount
of product formed.
B) By making the ΔG of the reaction more negative, enzymes increase the amount of
product formed per unit time.
C) By decreasing the energy of the transition state, enzymes increase the amount of
product formed per unit time.
D) By making the ΔG of the reaction more positive, enzymes increase the total amount
of product formed. CORRECT ANSWERS C) By decreasing the energy of the transition
state, enzymes increase the amount of product formed per unit time
Malate dehydrogenase is a key enzyme in TCA cycle, which catalyzes the following
reaction, which is unfavorable under standard conditions:
C4H6O5 + NAD+ -> C4H4O5 + NADH + H+
Which of the following corresponds to the compound that is most likely to be oxidized
under standard conditions?
A) C4H6O5
B) NAD+
C) C4H4O5
D) NADH CORRECT ANSWERS D) NADH
All of the following are examples of oxidation-reduction reactions EXCEPT:
I. C3H7O6P + NAD+ + Pi -> C3H8O10P2 + NADH + H+
II. C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O
III. C6H14O12P2 -> 2 C3H7O6P CORRECT ANSWERS III only
An acidic Glu residue in a protein (neutral in its protonated form) has a pKa value of 2.3
in the wild-type protein and is found near a neutral Ile residue. What will be the effect on
the pKa of the Glu residue if a mutation substitutes a positively charged Lys residue for
the Ile residue?
A) The pKa will decrease due to favorable ionic interactions between the deprotonated
Glu and Lys residues
, B) The pKa will decrease due to unfavorable ionic interactions between the
deprotonated Glu and Lys residues.
C) The pKa will increase due to favorable ionic interactions between the deprotonated
Glu and Lys residues.
D) The pKa will increase due to unfavorable ionic interactions between the
deprotonated Glu and Lys residues. CORRECT ANSWERS A) The pKa will decrease
due to favorable ionic interactions between the deprotonated Glu and Lys residues
Which of the following best orders the relative basicity of the side chains of Glu (pKa =
4.1), Cys (pKa = 8.3), and Lys (pKa = 10.8). CORRECT ANSWERS Lys > Cys > Glu
The cells in your body are constantly undergoing cellular respiration, producing CO2 as
a byproduct. What would happen to the pH of your blood if you were to hold your
breath?
A) It would increase.
B) It would be the same.
C) It would decrease.
D) It cannot be determined with the information provided. CORRECT ANSWERS C) It
would decrease
If a mutation changed an Arg residue in the protein interior to a Leu residue, what would
be the likely effect on the ΔG of protein folding?
A) ΔG would become more positive
B) ΔG would become more negative
C) ΔG would remain unchanged
D) The effect on ΔG cannot be determined without additional information. CORRECT
ANSWERS D) The effect on ΔG cannot be determined without additional information
Some inhibitors bind irreversibly to enzymes by covalent attachment. Would the kinetics
seen under these conditions (V vs. [S] curve) be similar to those seen with a reversible
noncompetitive inhibitor?
A) Yes, because it would reduce the Km of the reaction
B) Yes, because the net effect would be a loss of active enzyme available for the
reaction
C) No, because if enough substrate binds to the active site the reaction will reach Vmax
D) No, because Km will increase and Vmax will stay the same, similar to competitive
inhibition CORRECT ANSWERS B) Yes, because the net effect would be a loss of
active enzyme available for the reaction
Some enzymes can modify their substrate, and by this means, regulate its activity. In
many instances, these modifications are not permanent since other enzymes can
reverse them. Which of the following category of enzymes will irreversibly modify their
substrate?
(Freestanding Practice Questions And
Answers | Verified
Which of the following best describes the function of enzymes?
A) By decreasing the Ea, enzymes increase both the reaction rate and the total amount
of product formed.
B) By making the ΔG of the reaction more negative, enzymes increase the amount of
product formed per unit time.
C) By decreasing the energy of the transition state, enzymes increase the amount of
product formed per unit time.
D) By making the ΔG of the reaction more positive, enzymes increase the total amount
of product formed. CORRECT ANSWERS C) By decreasing the energy of the transition
state, enzymes increase the amount of product formed per unit time
Malate dehydrogenase is a key enzyme in TCA cycle, which catalyzes the following
reaction, which is unfavorable under standard conditions:
C4H6O5 + NAD+ -> C4H4O5 + NADH + H+
Which of the following corresponds to the compound that is most likely to be oxidized
under standard conditions?
A) C4H6O5
B) NAD+
C) C4H4O5
D) NADH CORRECT ANSWERS D) NADH
All of the following are examples of oxidation-reduction reactions EXCEPT:
I. C3H7O6P + NAD+ + Pi -> C3H8O10P2 + NADH + H+
II. C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O
III. C6H14O12P2 -> 2 C3H7O6P CORRECT ANSWERS III only
An acidic Glu residue in a protein (neutral in its protonated form) has a pKa value of 2.3
in the wild-type protein and is found near a neutral Ile residue. What will be the effect on
the pKa of the Glu residue if a mutation substitutes a positively charged Lys residue for
the Ile residue?
A) The pKa will decrease due to favorable ionic interactions between the deprotonated
Glu and Lys residues
, B) The pKa will decrease due to unfavorable ionic interactions between the
deprotonated Glu and Lys residues.
C) The pKa will increase due to favorable ionic interactions between the deprotonated
Glu and Lys residues.
D) The pKa will increase due to unfavorable ionic interactions between the
deprotonated Glu and Lys residues. CORRECT ANSWERS A) The pKa will decrease
due to favorable ionic interactions between the deprotonated Glu and Lys residues
Which of the following best orders the relative basicity of the side chains of Glu (pKa =
4.1), Cys (pKa = 8.3), and Lys (pKa = 10.8). CORRECT ANSWERS Lys > Cys > Glu
The cells in your body are constantly undergoing cellular respiration, producing CO2 as
a byproduct. What would happen to the pH of your blood if you were to hold your
breath?
A) It would increase.
B) It would be the same.
C) It would decrease.
D) It cannot be determined with the information provided. CORRECT ANSWERS C) It
would decrease
If a mutation changed an Arg residue in the protein interior to a Leu residue, what would
be the likely effect on the ΔG of protein folding?
A) ΔG would become more positive
B) ΔG would become more negative
C) ΔG would remain unchanged
D) The effect on ΔG cannot be determined without additional information. CORRECT
ANSWERS D) The effect on ΔG cannot be determined without additional information
Some inhibitors bind irreversibly to enzymes by covalent attachment. Would the kinetics
seen under these conditions (V vs. [S] curve) be similar to those seen with a reversible
noncompetitive inhibitor?
A) Yes, because it would reduce the Km of the reaction
B) Yes, because the net effect would be a loss of active enzyme available for the
reaction
C) No, because if enough substrate binds to the active site the reaction will reach Vmax
D) No, because Km will increase and Vmax will stay the same, similar to competitive
inhibition CORRECT ANSWERS B) Yes, because the net effect would be a loss of
active enzyme available for the reaction
Some enzymes can modify their substrate, and by this means, regulate its activity. In
many instances, these modifications are not permanent since other enzymes can
reverse them. Which of the following category of enzymes will irreversibly modify their
substrate?
