MCAT Exam and Practice Exam
2026/2027 Test Bank | AAMC Medical
College Admission Test Prep (400
Real Exam Questions &A+ Graded
Answers)
A researcher measures the rate of an enzyme-catalyzed reaction at increasing
substrate concentrations. The reaction rate initially increases rapidly but eventually
approaches a maximum value. Which enzyme property best explains this
observation?
A. The enzyme is consumed during the reaction
B. The enzyme becomes saturated with substrate
C. The substrate concentration decreases the activation energy indefinitely
D. The enzyme permanently changes into a product
B. The enzyme becomes saturated with substrate
Rationale: At sufficiently high substrate concentrations, essentially all available
enzyme active sites become occupied. The reaction therefore approaches Vmax,
producing the characteristic saturation curve.
Which amino acid is most likely to be found in the hydrophobic core of a soluble
globular protein?
A. Lysine
B. Aspartate
C. Leucine
D. Arginine
C. Leucine
,Rationale: Leucine has a nonpolar side chain and is commonly buried within the
hydrophobic interior of globular proteins, away from the aqueous environment.
A solution has a pH of 3. Compared with a solution having a pH of 5, the hydrogen
ion concentration is:
A. 2 times greater
B. 10 times greater
C. 100 times greater
D. 1,000 times greater
C. 100 times greater
Rationale: Each pH unit represents a tenfold change in hydrogen ion
concentration. A difference of two pH units therefore corresponds to 10², or 100-
fold.
Which organelle is primarily responsible for ATP production through oxidative
phosphorylation in eukaryotic cells?
A. Golgi apparatus
B. Lysosome
C. Mitochondrion
D. Endoplasmic reticulum
C. Mitochondrion
Rationale: The mitochondrial inner membrane contains the electron transport
chain and ATP synthase, which generate most cellular ATP through oxidative
phosphorylation.
A reaction has a positive ΔG under standard conditions. Which statement is most
accurate?
,A. The reaction must occur spontaneously in the forward direction
B. The reaction requires an input of free energy under those conditions
C. The reaction must have a negative activation energy
D. The reaction cannot occur under any conditions
B. The reaction requires an input of free energy under those conditions
Rationale: A positive ΔG indicates that the reaction is thermodynamically
unfavorable under the specified conditions. It may proceed if energy is supplied or
if conditions are altered.
What is the primary function of messenger RNA during protein synthesis?
A. Carry amino acids to the ribosome
B. Form the catalytic center of the ribosome
C. Carry genetic information from DNA to the ribosome
D. Replicate DNA before cell division
C. Carry genetic information from DNA to the ribosome
Rationale: mRNA is transcribed from DNA and carries codon information to
ribosomes, where the sequence is translated into a polypeptide.
Which process directly produces genetically different daughter cells during
meiosis?
A. DNA replication
B. Crossing over
C. Cytokinesis
D. Translation
B. Crossing over
Rationale: Crossing over occurs between homologous chromosomes during
prophase I of meiosis and creates new combinations of alleles.
, A patient has a deficiency of an enzyme involved in glycogen breakdown. Which
substance would most likely accumulate in the relevant metabolic pathway?
A. Glycogen
B. Oxygen
C. Carbon dioxide
D. Urea
A. Glycogen
Rationale: If glycogen cannot be efficiently degraded because of an enzyme
deficiency, glycogen or pathway intermediates upstream of the defective enzyme
can accumulate.
Which type of bond primarily stabilizes the complementary base pairing between
the two strands of DNA?
A. Peptide bonds
B. Hydrogen bonds
C. Ester bonds
D. Disulfide bonds
B. Hydrogen bonds
Rationale: Hydrogen bonds form between complementary nitrogenous bases:
adenine pairs with thymine, while guanine pairs with cytosine.
An object travels in a straight line at constant velocity. What is the net force acting
on the object?
A. Greater than zero
B. Less than zero
C. Equal to zero
D. Constantly increasing
C. Equal to zero
2026/2027 Test Bank | AAMC Medical
College Admission Test Prep (400
Real Exam Questions &A+ Graded
Answers)
A researcher measures the rate of an enzyme-catalyzed reaction at increasing
substrate concentrations. The reaction rate initially increases rapidly but eventually
approaches a maximum value. Which enzyme property best explains this
observation?
A. The enzyme is consumed during the reaction
B. The enzyme becomes saturated with substrate
C. The substrate concentration decreases the activation energy indefinitely
D. The enzyme permanently changes into a product
B. The enzyme becomes saturated with substrate
Rationale: At sufficiently high substrate concentrations, essentially all available
enzyme active sites become occupied. The reaction therefore approaches Vmax,
producing the characteristic saturation curve.
Which amino acid is most likely to be found in the hydrophobic core of a soluble
globular protein?
A. Lysine
B. Aspartate
C. Leucine
D. Arginine
C. Leucine
,Rationale: Leucine has a nonpolar side chain and is commonly buried within the
hydrophobic interior of globular proteins, away from the aqueous environment.
A solution has a pH of 3. Compared with a solution having a pH of 5, the hydrogen
ion concentration is:
A. 2 times greater
B. 10 times greater
C. 100 times greater
D. 1,000 times greater
C. 100 times greater
Rationale: Each pH unit represents a tenfold change in hydrogen ion
concentration. A difference of two pH units therefore corresponds to 10², or 100-
fold.
Which organelle is primarily responsible for ATP production through oxidative
phosphorylation in eukaryotic cells?
A. Golgi apparatus
B. Lysosome
C. Mitochondrion
D. Endoplasmic reticulum
C. Mitochondrion
Rationale: The mitochondrial inner membrane contains the electron transport
chain and ATP synthase, which generate most cellular ATP through oxidative
phosphorylation.
A reaction has a positive ΔG under standard conditions. Which statement is most
accurate?
,A. The reaction must occur spontaneously in the forward direction
B. The reaction requires an input of free energy under those conditions
C. The reaction must have a negative activation energy
D. The reaction cannot occur under any conditions
B. The reaction requires an input of free energy under those conditions
Rationale: A positive ΔG indicates that the reaction is thermodynamically
unfavorable under the specified conditions. It may proceed if energy is supplied or
if conditions are altered.
What is the primary function of messenger RNA during protein synthesis?
A. Carry amino acids to the ribosome
B. Form the catalytic center of the ribosome
C. Carry genetic information from DNA to the ribosome
D. Replicate DNA before cell division
C. Carry genetic information from DNA to the ribosome
Rationale: mRNA is transcribed from DNA and carries codon information to
ribosomes, where the sequence is translated into a polypeptide.
Which process directly produces genetically different daughter cells during
meiosis?
A. DNA replication
B. Crossing over
C. Cytokinesis
D. Translation
B. Crossing over
Rationale: Crossing over occurs between homologous chromosomes during
prophase I of meiosis and creates new combinations of alleles.
, A patient has a deficiency of an enzyme involved in glycogen breakdown. Which
substance would most likely accumulate in the relevant metabolic pathway?
A. Glycogen
B. Oxygen
C. Carbon dioxide
D. Urea
A. Glycogen
Rationale: If glycogen cannot be efficiently degraded because of an enzyme
deficiency, glycogen or pathway intermediates upstream of the defective enzyme
can accumulate.
Which type of bond primarily stabilizes the complementary base pairing between
the two strands of DNA?
A. Peptide bonds
B. Hydrogen bonds
C. Ester bonds
D. Disulfide bonds
B. Hydrogen bonds
Rationale: Hydrogen bonds form between complementary nitrogenous bases:
adenine pairs with thymine, while guanine pairs with cytosine.
An object travels in a straight line at constant velocity. What is the net force acting
on the object?
A. Greater than zero
B. Less than zero
C. Equal to zero
D. Constantly increasing
C. Equal to zero
