MCAT Advanced Practice Examination:
Comprehensive 150-Question Multiple-
Choice Assessment Covering Biological,
Chemical, Physical, Psychological, and
Critical Analysis Foundations for Medical
College Admission Test Preparation a well
detailed practice exam 2025/2026 graded A+
well written !!!
SECTION 1: BIOLOGICAL AND BIOCHEMICAL
FOUNDATIONS OF LIVING SYSTEMS (Questions 1–50)
Question 1
A researcher is studying a novel enzyme that catalyzes the conversion of substrate S to
product P. The enzyme exhibits Michaelis-Menten kinetics with a Km of 15 μM and a
Vmax of 120 μmol/min. In the presence of a competitive inhibitor, which of the
following changes would be observed?
,A) Decreased Km and decreased Vmax
B) Increased Km and unchanged Vmax
C) Unchanged Km and decreased Vmax
D) Increased Km and decreased Vmax
Correct Answer: B
Rationale: Competitive inhibitors bind to the active site of the enzyme, competing with
the substrate. This increases the apparent Km because more substrate is needed to
achieve half-maximal velocity, but Vmax remains unchanged because excess substrate
can outcompete the inhibitor.
Question 2
During the citric acid cycle, succinate dehydrogenase catalyzes the oxidation of
succinate to fumarate. This enzyme is unique among citric acid cycle enzymes because
it:
A) Is located in the mitochondrial matrix
B) Requires NAD⁺ as a cofactor
C) Is embedded in the inner mitochondrial membrane and uses FAD as a cofactor
D) Produces GTP via substrate-level phosphorylation
Correct Answer: C
Rationale: Succinate dehydrogenase is the only citric acid cycle enzyme that is
embedded in the inner mitochondrial membrane. It uses FAD (not NAD⁺) as a cofactor
because the redox potential of the succinate/fumarate couple is insufficient to reduce
NAD⁺.
Question 3
Which of the following statements about the lac operon is INCORRECT?
A) The lac repressor binds to the operator region in the absence of lactose
B) Allolactose acts as an inducer by binding to the repressor protein
,C) CAP (catabolite activator protein) binds to the promoter when glucose levels are high
D) The lac operon exhibits both negative and positive regulation
Correct Answer: C
Rationale: CAP binds to the promoter region only when cyclic AMP (cAMP) levels are
high, which occurs when glucose levels are low. When glucose is high, cAMP levels are
low, CAP does not bind, and transcription is reduced even in the presence of lactose.
Question 4
A patient presents with a deficiency in pyruvate dehydrogenase complex activity. Which
of the following metabolic consequences would most likely be observed?
A) Increased rate of glycolysis
B) Accumulation of acetyl-CoA
C) Decreased lactate production
D) Increased fatty acid synthesis
Correct Answer: A
Rationale: Pyruvate dehydrogenase converts pyruvate to acetyl-CoA. When this enzyme
is deficient, pyruvate cannot enter the citric acid cycle, leading to its accumulation and
increased conversion to lactate. The reduced production of acetyl-CoA would decrease
fatty acid synthesis and increase reliance on glycolysis.
Question 5
A biochemist isolates a protein that contains a high proportion of α-helices. The amino
acid sequence reveals recurring patterns of hydrophobic residues every 3–4 amino acids.
This structural feature most likely indicates:
A) The protein is a transmembrane domain
B) The protein undergoes alternative splicing
C) The protein is post-translationally modified
D) The protein forms a leucine zipper motif
, Correct Answer: A
Rationale: In transmembrane α-helices, hydrophobic residues appear every 3–4 amino
acids, corresponding to the helix pitch of approximately 3.6 residues per turn. This
creates a hydrophobic face that interacts with the lipid bilayer.
Question 6
In a population of cells, a mutation occurs in a gene encoding a DNA polymerase that
lacks 3'→5' exonuclease activity. The most likely consequence of this mutation is:
A) Increased rate of DNA replication
B) Decreased fidelity of DNA replication
C) Inability to synthesize Okazaki fragments
D) Loss of primase activity
Correct Answer: B
Rationale: The 3'→5' exonuclease activity of DNA polymerase provides proofreading
function. Without this activity, mismatched nucleotides are not removed, leading to a
higher mutation rate during DNA replication.
Question 7
Which of the following amino acid substitutions would most likely disrupt the tertiary
structure of a globular protein?
A) Valine to leucine
B) Aspartate to glutamate
C) Lysine to arginine
D) Glutamate to valine
Correct Answer: D
Rationale: Substituting a charged hydrophilic amino acid (glutamate) with a
hydrophobic amino acid (valine) would disrupt ionic interactions and hydrogen bonding
in the protein's core, severely affecting tertiary structure. Conservative substitutions (A,
B, C) are more likely to be tolerated.
Comprehensive 150-Question Multiple-
Choice Assessment Covering Biological,
Chemical, Physical, Psychological, and
Critical Analysis Foundations for Medical
College Admission Test Preparation a well
detailed practice exam 2025/2026 graded A+
well written !!!
SECTION 1: BIOLOGICAL AND BIOCHEMICAL
FOUNDATIONS OF LIVING SYSTEMS (Questions 1–50)
Question 1
A researcher is studying a novel enzyme that catalyzes the conversion of substrate S to
product P. The enzyme exhibits Michaelis-Menten kinetics with a Km of 15 μM and a
Vmax of 120 μmol/min. In the presence of a competitive inhibitor, which of the
following changes would be observed?
,A) Decreased Km and decreased Vmax
B) Increased Km and unchanged Vmax
C) Unchanged Km and decreased Vmax
D) Increased Km and decreased Vmax
Correct Answer: B
Rationale: Competitive inhibitors bind to the active site of the enzyme, competing with
the substrate. This increases the apparent Km because more substrate is needed to
achieve half-maximal velocity, but Vmax remains unchanged because excess substrate
can outcompete the inhibitor.
Question 2
During the citric acid cycle, succinate dehydrogenase catalyzes the oxidation of
succinate to fumarate. This enzyme is unique among citric acid cycle enzymes because
it:
A) Is located in the mitochondrial matrix
B) Requires NAD⁺ as a cofactor
C) Is embedded in the inner mitochondrial membrane and uses FAD as a cofactor
D) Produces GTP via substrate-level phosphorylation
Correct Answer: C
Rationale: Succinate dehydrogenase is the only citric acid cycle enzyme that is
embedded in the inner mitochondrial membrane. It uses FAD (not NAD⁺) as a cofactor
because the redox potential of the succinate/fumarate couple is insufficient to reduce
NAD⁺.
Question 3
Which of the following statements about the lac operon is INCORRECT?
A) The lac repressor binds to the operator region in the absence of lactose
B) Allolactose acts as an inducer by binding to the repressor protein
,C) CAP (catabolite activator protein) binds to the promoter when glucose levels are high
D) The lac operon exhibits both negative and positive regulation
Correct Answer: C
Rationale: CAP binds to the promoter region only when cyclic AMP (cAMP) levels are
high, which occurs when glucose levels are low. When glucose is high, cAMP levels are
low, CAP does not bind, and transcription is reduced even in the presence of lactose.
Question 4
A patient presents with a deficiency in pyruvate dehydrogenase complex activity. Which
of the following metabolic consequences would most likely be observed?
A) Increased rate of glycolysis
B) Accumulation of acetyl-CoA
C) Decreased lactate production
D) Increased fatty acid synthesis
Correct Answer: A
Rationale: Pyruvate dehydrogenase converts pyruvate to acetyl-CoA. When this enzyme
is deficient, pyruvate cannot enter the citric acid cycle, leading to its accumulation and
increased conversion to lactate. The reduced production of acetyl-CoA would decrease
fatty acid synthesis and increase reliance on glycolysis.
Question 5
A biochemist isolates a protein that contains a high proportion of α-helices. The amino
acid sequence reveals recurring patterns of hydrophobic residues every 3–4 amino acids.
This structural feature most likely indicates:
A) The protein is a transmembrane domain
B) The protein undergoes alternative splicing
C) The protein is post-translationally modified
D) The protein forms a leucine zipper motif
, Correct Answer: A
Rationale: In transmembrane α-helices, hydrophobic residues appear every 3–4 amino
acids, corresponding to the helix pitch of approximately 3.6 residues per turn. This
creates a hydrophobic face that interacts with the lipid bilayer.
Question 6
In a population of cells, a mutation occurs in a gene encoding a DNA polymerase that
lacks 3'→5' exonuclease activity. The most likely consequence of this mutation is:
A) Increased rate of DNA replication
B) Decreased fidelity of DNA replication
C) Inability to synthesize Okazaki fragments
D) Loss of primase activity
Correct Answer: B
Rationale: The 3'→5' exonuclease activity of DNA polymerase provides proofreading
function. Without this activity, mismatched nucleotides are not removed, leading to a
higher mutation rate during DNA replication.
Question 7
Which of the following amino acid substitutions would most likely disrupt the tertiary
structure of a globular protein?
A) Valine to leucine
B) Aspartate to glutamate
C) Lysine to arginine
D) Glutamate to valine
Correct Answer: D
Rationale: Substituting a charged hydrophilic amino acid (glutamate) with a
hydrophobic amino acid (valine) would disrupt ionic interactions and hydrogen bonding
in the protein's core, severely affecting tertiary structure. Conservative substitutions (A,
B, C) are more likely to be tolerated.
