MCAT Biochemistry Practice Questions
With 100% Correct Answers
In a neutral solution, most amino acids exist as:
A. positively charged compounds
B. zwitterions
C. negatively charged compounds
D. hydrophobic molecules CORRECT ANSWERS B
At pH 7, the charge on a glutamic acid molecules is:
A. -2
B. -1
C. 0
D. +1 CORRECT ANSWERS B
Which of the following statements is most likely to be true of nonpolar R groups in
aqueous solution?
A. They are hydrophilic and found buried with proteins
B. They are hydrophilic and found on protein surfaces
C. They are hydrophobic and found buried within proteins
D. They are hydrophobic and found on protein surfaces CORRECT ANSWERS C
Which of these statements concerning peptide bonds is FALSE?
A. There formation involves a reaction between an amino group and a carboxyl group
B. They are the primary bonds that hold amino acids together
C. They have partial double bond character
D. Their formation involves hydration reactions CORRECT ANSWERS D
How many distinct tripeptides can be formed from one valine molecule, one alanine
molecule, and one leucine molecule?
A. 1
B. 3
C. 6
D. 27 CORRECT ANSWERS C
Which of these structures is most likely to be preserved when a protein is denatured?
A. Primary structure
B. Secondary structure
,C. Tertiary structure
D. Quaternary structure CORRECT ANSWERS A
An alpha-helix is most likely held together by:
A. disulfide bonds
B. hydrophobic effects
C. hydrogen bonds
D. ionic attractions between side chains CORRECT ANSWERS C
Which of the following is least likely to cause denaturation of proteins?
A. Heating the protein to 100 degrees C
B. Adding 8M urea
C. Moving it to a more hypotonic environment
D. Adding a detergent such as sodium dodecyl sulfate CORRECT ANSWERS C
A particular alpha-helix is known to cross the cell membrane. Which of these amino
acids is most likely to be found in the transmembrane portion of the helix?
A. Glutamate
B. Lysine
C. Phenylalanine
D. Aspartate CORRECT ANSWERS C
Which of these amino acids has a chiral carbon in its side chain?
I. Serine
II. Threonine
III. Isoleucine
A. I only
B. II only
C. II and III only
D. I, II and III CORRECT ANSWERS C
Adding concentrated strong base to a solution containing an enzyme often reduces
enzyme activity to zero. In addition to causing protein denaturation which of the
following is another plausible reason of the loss of enzyme activity?
A. Enzyme activity, once lost, cannot be recovered
B. The base can cleave peptide residues
C. Adding a base catalyzes protein polymerization
D. Adding a base tends to deprotonate amino acids on the surface of proteins
CORRECT ANSWERS B
Which of these amino acids has a side chain that can become ionized in cells?
,A. Histidine
B. Leucine
C. Proline
D. Theronine CORRECT ANSWERS A
In lysine, the pKa of the side chain is about 10.5. Assuming that the pKa of the carboxyl
and amino groups are 2 and 9 respectively, the pI of lysine is closest to:
A) 5.5
B) 6.2
C) 7.4
D) 9.8 CORRECT ANSWERS D
Which of the following is a reason for conjugating proteins?
I. To direct their delivery to a particular organelle
II. To direct their delivery to the cell membrane
III. To add a cofactor needed for their activity
A. I only
B. II only
C. II and III only
D. I, II and III CORRECT ANSWERS D
Collagen consists of three helices with carbon backbones that are tightly wrapped
around one another in a "triple helix." Which of these amino acids is most likely to be
found in the highest concentration in collagen?
A. Proline
B. Glycine
C. Threonine
D. Cysteine CORRECT ANSWERS B
Consider a biochemical reaction A -> B, which is catalyzed by A-B dehydrogenase.
Which of the following statements is true?
A. The reaction will proceed until the enzyme concentration decreases
B. The reaction will be most favorable at 0 degrees C
C. A component of the enzyme if transferred from A to B
D. The free energy change (deltaG) of the catalyzed reaction is the same as for the
uncatalyzed reaction CORRECT ANSWERS D
Which of the following statements about enzyme kinetics is FALSE?
A. An increase in the substrate concentration (at constant enzyme concentration) leads
to proportional increases in the rate of the reaction
, B. Most enzymes operating in the human body work best at a temperature of 37
degrees C
C. An enzyme-substrate complex can either forma product or dissociate back into the
enzyme and substrate
D. Maximal activity of many human enzymes occurs around pH 7.4 CORRECT
ANSWERS A
Some enzymes require the presence of a nonprotein molecule to behave catalytically.
An enzyme devoid of this molecule is called a(n)
A. holenzyme
B. apoenzyme
C. coenzyme
D. zymoenzyme CORRECT ANSWERS B
Which of the following factor determine an enzyme's specificity?
A. The three-dimensional shape of the active site
B. The Michaelis constant
C. The type of cofactor required for the enzyme to be active
D. The prosthetic group of the enzyme CORRECT ANSWERS A
Enzymes increase the rate of a reaction by:
A. decreasing the activation energy
B. decreasing the overall free energy change of the reaction
C. increasing the activation energy
D. increasing the overall free energy change of the reaction CORRECT ANSWERS A
In the equation below, substrate C is an allosteric inhibitor to enzyme 1. Which of the
following is another mechanism necessarily caused by substrate C?
A -(enzyme 1)-> B -(enzyme 2)-> C
A. Competitive inhibition
B. Irreversible inhibition
C. Feedback enhancement
D. Negative feedback CORRECT ANSWERS D
Consider a reaction catalyzed by enzyme A with a Km value of 5x10^-6M and Vmax of
20 mol/min. At a concentration of 5x10^-6 m substrate the rate of the reaction will be:
A. 10 mmol/min
B. 15 mmol/min
C. 20 mmol/min
D. 30 mmol/min CORRECT ANSWERS A
With 100% Correct Answers
In a neutral solution, most amino acids exist as:
A. positively charged compounds
B. zwitterions
C. negatively charged compounds
D. hydrophobic molecules CORRECT ANSWERS B
At pH 7, the charge on a glutamic acid molecules is:
A. -2
B. -1
C. 0
D. +1 CORRECT ANSWERS B
Which of the following statements is most likely to be true of nonpolar R groups in
aqueous solution?
A. They are hydrophilic and found buried with proteins
B. They are hydrophilic and found on protein surfaces
C. They are hydrophobic and found buried within proteins
D. They are hydrophobic and found on protein surfaces CORRECT ANSWERS C
Which of these statements concerning peptide bonds is FALSE?
A. There formation involves a reaction between an amino group and a carboxyl group
B. They are the primary bonds that hold amino acids together
C. They have partial double bond character
D. Their formation involves hydration reactions CORRECT ANSWERS D
How many distinct tripeptides can be formed from one valine molecule, one alanine
molecule, and one leucine molecule?
A. 1
B. 3
C. 6
D. 27 CORRECT ANSWERS C
Which of these structures is most likely to be preserved when a protein is denatured?
A. Primary structure
B. Secondary structure
,C. Tertiary structure
D. Quaternary structure CORRECT ANSWERS A
An alpha-helix is most likely held together by:
A. disulfide bonds
B. hydrophobic effects
C. hydrogen bonds
D. ionic attractions between side chains CORRECT ANSWERS C
Which of the following is least likely to cause denaturation of proteins?
A. Heating the protein to 100 degrees C
B. Adding 8M urea
C. Moving it to a more hypotonic environment
D. Adding a detergent such as sodium dodecyl sulfate CORRECT ANSWERS C
A particular alpha-helix is known to cross the cell membrane. Which of these amino
acids is most likely to be found in the transmembrane portion of the helix?
A. Glutamate
B. Lysine
C. Phenylalanine
D. Aspartate CORRECT ANSWERS C
Which of these amino acids has a chiral carbon in its side chain?
I. Serine
II. Threonine
III. Isoleucine
A. I only
B. II only
C. II and III only
D. I, II and III CORRECT ANSWERS C
Adding concentrated strong base to a solution containing an enzyme often reduces
enzyme activity to zero. In addition to causing protein denaturation which of the
following is another plausible reason of the loss of enzyme activity?
A. Enzyme activity, once lost, cannot be recovered
B. The base can cleave peptide residues
C. Adding a base catalyzes protein polymerization
D. Adding a base tends to deprotonate amino acids on the surface of proteins
CORRECT ANSWERS B
Which of these amino acids has a side chain that can become ionized in cells?
,A. Histidine
B. Leucine
C. Proline
D. Theronine CORRECT ANSWERS A
In lysine, the pKa of the side chain is about 10.5. Assuming that the pKa of the carboxyl
and amino groups are 2 and 9 respectively, the pI of lysine is closest to:
A) 5.5
B) 6.2
C) 7.4
D) 9.8 CORRECT ANSWERS D
Which of the following is a reason for conjugating proteins?
I. To direct their delivery to a particular organelle
II. To direct their delivery to the cell membrane
III. To add a cofactor needed for their activity
A. I only
B. II only
C. II and III only
D. I, II and III CORRECT ANSWERS D
Collagen consists of three helices with carbon backbones that are tightly wrapped
around one another in a "triple helix." Which of these amino acids is most likely to be
found in the highest concentration in collagen?
A. Proline
B. Glycine
C. Threonine
D. Cysteine CORRECT ANSWERS B
Consider a biochemical reaction A -> B, which is catalyzed by A-B dehydrogenase.
Which of the following statements is true?
A. The reaction will proceed until the enzyme concentration decreases
B. The reaction will be most favorable at 0 degrees C
C. A component of the enzyme if transferred from A to B
D. The free energy change (deltaG) of the catalyzed reaction is the same as for the
uncatalyzed reaction CORRECT ANSWERS D
Which of the following statements about enzyme kinetics is FALSE?
A. An increase in the substrate concentration (at constant enzyme concentration) leads
to proportional increases in the rate of the reaction
, B. Most enzymes operating in the human body work best at a temperature of 37
degrees C
C. An enzyme-substrate complex can either forma product or dissociate back into the
enzyme and substrate
D. Maximal activity of many human enzymes occurs around pH 7.4 CORRECT
ANSWERS A
Some enzymes require the presence of a nonprotein molecule to behave catalytically.
An enzyme devoid of this molecule is called a(n)
A. holenzyme
B. apoenzyme
C. coenzyme
D. zymoenzyme CORRECT ANSWERS B
Which of the following factor determine an enzyme's specificity?
A. The three-dimensional shape of the active site
B. The Michaelis constant
C. The type of cofactor required for the enzyme to be active
D. The prosthetic group of the enzyme CORRECT ANSWERS A
Enzymes increase the rate of a reaction by:
A. decreasing the activation energy
B. decreasing the overall free energy change of the reaction
C. increasing the activation energy
D. increasing the overall free energy change of the reaction CORRECT ANSWERS A
In the equation below, substrate C is an allosteric inhibitor to enzyme 1. Which of the
following is another mechanism necessarily caused by substrate C?
A -(enzyme 1)-> B -(enzyme 2)-> C
A. Competitive inhibition
B. Irreversible inhibition
C. Feedback enhancement
D. Negative feedback CORRECT ANSWERS D
Consider a reaction catalyzed by enzyme A with a Km value of 5x10^-6M and Vmax of
20 mol/min. At a concentration of 5x10^-6 m substrate the rate of the reaction will be:
A. 10 mmol/min
B. 15 mmol/min
C. 20 mmol/min
D. 30 mmol/min CORRECT ANSWERS A
