MCAT Advanced Practice Examination v2.0:
Comprehensive 150-Question Multiple-
Choice Assessment 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 the regulation of the trp operon in E. coli. When tryptophan levels are
high, which of the following mechanisms is primarily responsible for reduced transcription?
A) The repressor protein binds to the operator only when tryptophan is absent
B) Tryptophan acts as a corepressor, enabling the repressor to bind the operator
C) The attenuator region forms a terminator hairpin structure in the mRNA
D) Both B and C
Correct Answer: D
Rationale: The trp operon is regulated by two mechanisms: (1) repression, where tryptophan
acts as a corepressor enabling the repressor to bind the operator, and (2) attenuation, where
high tryptophan levels allow formation of a terminator hairpin that causes premature
transcription termination.
Question 2
A patient with a deficiency in the enzyme that converts phenylalanine to tyrosine would most
likely present with:
,A) Alkaptonuria
B) Phenylketonuria (PKU)
C) Maple syrup urine disease
D) Homocystinuria
Correct Answer: B
Rationale: Phenylketonuria (PKU) results from a deficiency in phenylalanine hydroxylase, which
converts phenylalanine to tyrosine. This leads to accumulation of phenylalanine and its
metabolites, causing intellectual disability if untreated.
Question 3
Which of the following describes the role of the proteasome in cellular protein degradation?
A) It degrades proteins in lysosomes
B) It selectively degrades ubiquitin-tagged proteins in the cytosol and nucleus
C) It degrades proteins in the endoplasmic reticulum
D) It cleaves signal peptides from proteins entering the ER
Correct Answer: B
Rationale: The proteasome is a large protein complex that selectively degrades proteins marked
with ubiquitin in the cytosol and nucleus. Lysosomes degrade proteins via autophagy, and the
ER has its own quality control degradation system.
Question 4
During DNA replication, the leading strand is synthesized:
A) Discontinuously in the 5'→3' direction away from the replication fork
B) Continuously in the 5'→3' direction toward the replication fork
C) Discontinuously in the 3'→5' direction toward the replication fork
D) Continuously in the 3'→5' direction away from the replication fork
Correct Answer: B
Rationale: The leading strand is synthesized continuously in the 5'→3' direction toward the
replication fork, following the same direction as helicase movement. The lagging strand is
synthesized discontinuously away from the fork.
Question 5
,Which of the following is the correct sequence of events in the initiation of translation in
eukaryotes?
A) Ribosome binds mRNA → initiator tRNA binds → scanning for start codon
B) Initiator tRNA binds ribosome → ribosome binds mRNA → scanning for start codon
C) Ribosome binds mRNA → scanning for start codon → initiator tRNA binds
D) Initiator tRNA binds mRNA → ribosome binds → scanning for start codon
Correct Answer: B
Rationale: In eukaryotic translation initiation, the initiator tRNA (Met-tRNAi) binds to the small
ribosomal subunit, which then binds to the 5' cap of mRNA and scans for the start codon (AUG).
The large subunit then joins.
Question 6
A biochemist discovers a new enzyme that catalyzes the reaction S → P. The enzyme has a Vmax
of 50 μmol/min and a Km of 2 mM. At a substrate concentration of 6 mM, what is the reaction
velocity?
A) 25 μmol/min
B) 37.5 μmol/min
C) 45 μmol/min
D) 50 μmol/min
Correct Answer: B
Rationale: Using the Michaelis-Menten equation: v = (Vmax × [S])/(Km + [S]) = (50 × 6)/(2 + 6) =
300/8 = 37.5 μmol/min.
Question 7
Which of the following correctly matches the vitamin with its coenzyme form?
A) Niacin → FAD
B) Riboflavin → NAD⁺
C) Vitamin B₆ → Pyridoxal phosphate
D) Thiamine → Coenzyme A
Correct Answer: C
Rationale: Vitamin B₆ (pyridoxine) is converted to pyridoxal phosphate (PLP), a coenzyme for
, amino acid metabolism. Niacin → NAD⁺/NADP⁺, Riboflavin → FAD/FMN, Thiamine → TPP, and
Pantothenic acid → Coenzyme A.
Question 8
A researcher observes that a cell line undergoes apoptosis when treated with a drug. Which of
the following molecular events is most likely occurring?
A) Activation of caspases
B) Inhibition of cytochrome c release from mitochondria
C) Decreased Bax expression
D) Increased Bcl-2 activity
Correct Answer: A
Rationale: Apoptosis is executed by caspases, a family of cysteine-aspartic proteases.
Cytochrome c release, Bax activation, and Bcl-2 inhibition are upstream events that lead to
caspase activation, not the final execution.
Question 9
The conversion of glucose to glucose-6-phosphate is catalyzed by hexokinase. This reaction is:
A) Endergonic and requires ATP
B) Exergonic and produces ATP
C) Endergonic and produces ATP
D) Exergonic and requires ATP
Correct Answer: A
Rationale: The phosphorylation of glucose to glucose-6-phosphate is endergonic (requires
energy input) and is coupled to ATP hydrolysis. The reaction has a positive ΔG and requires ATP
to proceed.
Question 10
Which of the following statements about the genetic code is INCORRECT?
A) The code is degenerate
B) The code is universal across all organisms
Comprehensive 150-Question Multiple-
Choice Assessment 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 the regulation of the trp operon in E. coli. When tryptophan levels are
high, which of the following mechanisms is primarily responsible for reduced transcription?
A) The repressor protein binds to the operator only when tryptophan is absent
B) Tryptophan acts as a corepressor, enabling the repressor to bind the operator
C) The attenuator region forms a terminator hairpin structure in the mRNA
D) Both B and C
Correct Answer: D
Rationale: The trp operon is regulated by two mechanisms: (1) repression, where tryptophan
acts as a corepressor enabling the repressor to bind the operator, and (2) attenuation, where
high tryptophan levels allow formation of a terminator hairpin that causes premature
transcription termination.
Question 2
A patient with a deficiency in the enzyme that converts phenylalanine to tyrosine would most
likely present with:
,A) Alkaptonuria
B) Phenylketonuria (PKU)
C) Maple syrup urine disease
D) Homocystinuria
Correct Answer: B
Rationale: Phenylketonuria (PKU) results from a deficiency in phenylalanine hydroxylase, which
converts phenylalanine to tyrosine. This leads to accumulation of phenylalanine and its
metabolites, causing intellectual disability if untreated.
Question 3
Which of the following describes the role of the proteasome in cellular protein degradation?
A) It degrades proteins in lysosomes
B) It selectively degrades ubiquitin-tagged proteins in the cytosol and nucleus
C) It degrades proteins in the endoplasmic reticulum
D) It cleaves signal peptides from proteins entering the ER
Correct Answer: B
Rationale: The proteasome is a large protein complex that selectively degrades proteins marked
with ubiquitin in the cytosol and nucleus. Lysosomes degrade proteins via autophagy, and the
ER has its own quality control degradation system.
Question 4
During DNA replication, the leading strand is synthesized:
A) Discontinuously in the 5'→3' direction away from the replication fork
B) Continuously in the 5'→3' direction toward the replication fork
C) Discontinuously in the 3'→5' direction toward the replication fork
D) Continuously in the 3'→5' direction away from the replication fork
Correct Answer: B
Rationale: The leading strand is synthesized continuously in the 5'→3' direction toward the
replication fork, following the same direction as helicase movement. The lagging strand is
synthesized discontinuously away from the fork.
Question 5
,Which of the following is the correct sequence of events in the initiation of translation in
eukaryotes?
A) Ribosome binds mRNA → initiator tRNA binds → scanning for start codon
B) Initiator tRNA binds ribosome → ribosome binds mRNA → scanning for start codon
C) Ribosome binds mRNA → scanning for start codon → initiator tRNA binds
D) Initiator tRNA binds mRNA → ribosome binds → scanning for start codon
Correct Answer: B
Rationale: In eukaryotic translation initiation, the initiator tRNA (Met-tRNAi) binds to the small
ribosomal subunit, which then binds to the 5' cap of mRNA and scans for the start codon (AUG).
The large subunit then joins.
Question 6
A biochemist discovers a new enzyme that catalyzes the reaction S → P. The enzyme has a Vmax
of 50 μmol/min and a Km of 2 mM. At a substrate concentration of 6 mM, what is the reaction
velocity?
A) 25 μmol/min
B) 37.5 μmol/min
C) 45 μmol/min
D) 50 μmol/min
Correct Answer: B
Rationale: Using the Michaelis-Menten equation: v = (Vmax × [S])/(Km + [S]) = (50 × 6)/(2 + 6) =
300/8 = 37.5 μmol/min.
Question 7
Which of the following correctly matches the vitamin with its coenzyme form?
A) Niacin → FAD
B) Riboflavin → NAD⁺
C) Vitamin B₆ → Pyridoxal phosphate
D) Thiamine → Coenzyme A
Correct Answer: C
Rationale: Vitamin B₆ (pyridoxine) is converted to pyridoxal phosphate (PLP), a coenzyme for
, amino acid metabolism. Niacin → NAD⁺/NADP⁺, Riboflavin → FAD/FMN, Thiamine → TPP, and
Pantothenic acid → Coenzyme A.
Question 8
A researcher observes that a cell line undergoes apoptosis when treated with a drug. Which of
the following molecular events is most likely occurring?
A) Activation of caspases
B) Inhibition of cytochrome c release from mitochondria
C) Decreased Bax expression
D) Increased Bcl-2 activity
Correct Answer: A
Rationale: Apoptosis is executed by caspases, a family of cysteine-aspartic proteases.
Cytochrome c release, Bax activation, and Bcl-2 inhibition are upstream events that lead to
caspase activation, not the final execution.
Question 9
The conversion of glucose to glucose-6-phosphate is catalyzed by hexokinase. This reaction is:
A) Endergonic and requires ATP
B) Exergonic and produces ATP
C) Endergonic and produces ATP
D) Exergonic and requires ATP
Correct Answer: A
Rationale: The phosphorylation of glucose to glucose-6-phosphate is endergonic (requires
energy input) and is coupled to ATP hydrolysis. The reaction has a positive ΔG and requires ATP
to proceed.
Question 10
Which of the following statements about the genetic code is INCORRECT?
A) The code is degenerate
B) The code is universal across all organisms
