MCAT BIOLOGICAL SCIENCES
REVIEW EXAM |||questions and
answers with rationales/graded
A+/2026 update/100% correct
/instant download
2026-2027 | COMPLETE PREP
Total Questions: 85
Sections:
• Molecular Biology & Biochemistry (Q1-20)
• Cellular Biology (Q21-35)
• Genetics & Evolution (Q36-50)
• Organ Systems & Physiology (Q51-70)
• Microbiology & Immunology (Q71-85)
Instructions: Choose the best answer. Correct answers are highlighted in bold.
Section 1: Molecular Biology & Biochemistry (Q1-20)
Q1. Which of the following best describes the primary role of the enzyme helicase
in DNA replication?
A) Relieves supercoiling ahead of the replication fork
B) Synthesizes RNA primers
C) Unwinds the DNA double helix
D) Seals nicks in the sugar-phosphate backbone
,Rationale: Helicase breaks hydrogen bonds between complementary bases,
unwinding DNA. Topoisomerase (A) relieves supercoiling. Primase (B)
synthesizes RNA primers. Ligase (D) seals nicks.
Q2. A mutation in the promoter region of a gene most directly affects:
A) mRNA splicing
B) Transcription initiation
C) Protein folding
D) Ribosome binding
Rationale: Promoters are binding sites for RNA polymerase and transcription
factors; mutations alter transcription initiation. Splicing (A) is post-transcriptional.
Protein folding occurs after translation.
Q3. Which amino acid residue is most likely found in the transmembrane domain
of an integral membrane protein?
A) Leucine
B) Arginine
C) Glutamate
D) Serine
Rationale: Leucine is nonpolar/hydrophobic, ideal for lipid bilayer. Arginine &
glutamate are charged, serine is polar—these prefer aqueous environments.
Q4. During competitive inhibition of an enzyme, which kinetic parameter
changes?
A) Vmax unchanged, Km increased
B) Vmax decreased, Km unchanged
C) Both Vmax and Km decreased
D) Both Vmax and Km increased
Rationale: Competitive inhibitor binds active site, raising apparent Km (more
substrate needed to reach half Vmax); Vmax same since excess substrate
overcomes inhibition.
Q5. The final electron acceptor in the electron transport chain during aerobic
respiration is:
A) NAD+
B) FAD
C) Cytochrome c
D) Oxygen
, Rationale: O2 is reduced to H2O at Complex IV. NAD+ and FAD are electron
carriers, not final acceptors. Cytochrome c shuttles electrons.
Q6. Which of the following is a characteristic of allosteric enzyme regulation?
A) Binding of inhibitor at active site
B) Binding of effector at a distinct site, altering substrate affinity
C) Irreversible covalent modification
D) No change in Vmax
Rationale: Allosteric effectors bind regulatory sites, changing conformation and
substrate affinity (Km) and often Vmax. Active site binding is competitive.
Q7. In the lac operon, in the presence of lactose but absence of glucose:
A) cAMP high, CAP active, repressor inactive
B) cAMP low, CAP inactive, repressor active
C) cAMP high, CAP active, repressor active
D) cAMP low, CAP inactive, repressor inactive
Rationale: Low glucose → high cAMP → CAP binds activator site. Lactose binds
repressor, inactivating it. Both needed for maximal transcription.
Q8. The conversion of pyruvate to acetyl-CoA occurs in the:
A) Cytosol
B) Mitochondrial matrix
C) Inner mitochondrial membrane
D) Nucleus
Rationale: Pyruvate dehydrogenase complex is located in the mitochondrial
matrix. Cytosol contains glycolysis.
Q9. Which technique separates proteins based solely on molecular weight under
denaturing conditions?
A) SDS-PAGE
B) Ion-exchange chromatography
C) Affinity chromatography
D) Native PAGE
Rationale: SDS denatures proteins and gives uniform charge-to-mass ratio;
migration depends only on mass. Native PAGE preserves structure/charge.
Q10. A patient has a defect in carnitine acyltransferase I. Which process is directly
impaired?
REVIEW EXAM |||questions and
answers with rationales/graded
A+/2026 update/100% correct
/instant download
2026-2027 | COMPLETE PREP
Total Questions: 85
Sections:
• Molecular Biology & Biochemistry (Q1-20)
• Cellular Biology (Q21-35)
• Genetics & Evolution (Q36-50)
• Organ Systems & Physiology (Q51-70)
• Microbiology & Immunology (Q71-85)
Instructions: Choose the best answer. Correct answers are highlighted in bold.
Section 1: Molecular Biology & Biochemistry (Q1-20)
Q1. Which of the following best describes the primary role of the enzyme helicase
in DNA replication?
A) Relieves supercoiling ahead of the replication fork
B) Synthesizes RNA primers
C) Unwinds the DNA double helix
D) Seals nicks in the sugar-phosphate backbone
,Rationale: Helicase breaks hydrogen bonds between complementary bases,
unwinding DNA. Topoisomerase (A) relieves supercoiling. Primase (B)
synthesizes RNA primers. Ligase (D) seals nicks.
Q2. A mutation in the promoter region of a gene most directly affects:
A) mRNA splicing
B) Transcription initiation
C) Protein folding
D) Ribosome binding
Rationale: Promoters are binding sites for RNA polymerase and transcription
factors; mutations alter transcription initiation. Splicing (A) is post-transcriptional.
Protein folding occurs after translation.
Q3. Which amino acid residue is most likely found in the transmembrane domain
of an integral membrane protein?
A) Leucine
B) Arginine
C) Glutamate
D) Serine
Rationale: Leucine is nonpolar/hydrophobic, ideal for lipid bilayer. Arginine &
glutamate are charged, serine is polar—these prefer aqueous environments.
Q4. During competitive inhibition of an enzyme, which kinetic parameter
changes?
A) Vmax unchanged, Km increased
B) Vmax decreased, Km unchanged
C) Both Vmax and Km decreased
D) Both Vmax and Km increased
Rationale: Competitive inhibitor binds active site, raising apparent Km (more
substrate needed to reach half Vmax); Vmax same since excess substrate
overcomes inhibition.
Q5. The final electron acceptor in the electron transport chain during aerobic
respiration is:
A) NAD+
B) FAD
C) Cytochrome c
D) Oxygen
, Rationale: O2 is reduced to H2O at Complex IV. NAD+ and FAD are electron
carriers, not final acceptors. Cytochrome c shuttles electrons.
Q6. Which of the following is a characteristic of allosteric enzyme regulation?
A) Binding of inhibitor at active site
B) Binding of effector at a distinct site, altering substrate affinity
C) Irreversible covalent modification
D) No change in Vmax
Rationale: Allosteric effectors bind regulatory sites, changing conformation and
substrate affinity (Km) and often Vmax. Active site binding is competitive.
Q7. In the lac operon, in the presence of lactose but absence of glucose:
A) cAMP high, CAP active, repressor inactive
B) cAMP low, CAP inactive, repressor active
C) cAMP high, CAP active, repressor active
D) cAMP low, CAP inactive, repressor inactive
Rationale: Low glucose → high cAMP → CAP binds activator site. Lactose binds
repressor, inactivating it. Both needed for maximal transcription.
Q8. The conversion of pyruvate to acetyl-CoA occurs in the:
A) Cytosol
B) Mitochondrial matrix
C) Inner mitochondrial membrane
D) Nucleus
Rationale: Pyruvate dehydrogenase complex is located in the mitochondrial
matrix. Cytosol contains glycolysis.
Q9. Which technique separates proteins based solely on molecular weight under
denaturing conditions?
A) SDS-PAGE
B) Ion-exchange chromatography
C) Affinity chromatography
D) Native PAGE
Rationale: SDS denatures proteins and gives uniform charge-to-mass ratio;
migration depends only on mass. Native PAGE preserves structure/charge.
Q10. A patient has a defect in carnitine acyltransferase I. Which process is directly
impaired?
