MCAT AAMC Practice Exam 3 Questions with
Correct Answers and Rationale | Graded A+ | New
2026-2027 Update
Question 1
Compound 1 is used to treat HIV infection based on its ability to act as:
A. an agonist.
B. an antagonist.
C. a placebo.
D. a catalyst.
Correct Answer: B. an antagonist.
Rationale: This is a Biochemistry question that falls under content category
"Principles of chemical thermodynamics and kinetics." Compound 1 binds to the
transition state of HIV protease and serves to treat infection. It is clearly inhibiting
this enzyme through its binding and thus serves as an antagonist. This question
requires Knowledge of Scientific Concepts and Principles, specifically the
definition of an antagonist, to arrive at the answer. The passage states: "One such
molecule is Compound 1, shown in Figure 2, which is a potent HIV protease
inhibitor."
Question 2
How many stereoisomers of Compound 1 exist?
A. 8
B. 16
C. 32
D. 64
Correct Answer: C. 32
,Rationale: This is an Organic Chemistry question that falls under the content
category "Nature of molecules and intermolecular interactions." There are 5
chirality centers in Compound 1. By application of the 2ⁿ rule, there are 2⁵ = 32
possible stereoisomers. This question requires Scientific Reasoning and Problem
Solving to arrive at the answer.
Question 3
Why do kidney stones form in some individuals treated with Compound 1?
A. [Ca²⁺] + [C₂O₄²⁻] > Ksp
B. [Ca²⁺][C₂O₄²⁻] > Ksp
C. [Ca²⁺] + [C₂O₄²⁻] < Ksp
D. [Ca²⁺][C₂O₄²⁻] < Ksp
Correct Answer: B. [Ca²⁺][C₂O₄²⁻] > Ksp
Rationale: This is a General Chemistry question that falls under the content
category "Unique nature of water and its solutions." Calcium oxalate precipitates
when [Ca²⁺][C₂O₄²⁻] exceeds the solubility product constant Ksp by definition. This
question requires Scientific Reasoning and Problem Solving to arrive at the
answer.
Question 4
The peptide bond between which two amino acid residues is cleaved by HIV
protease?
A. Phe and Ala
B. Pro and Val
C. Val and Ala
D. Phe and Pro
Correct Answer: D. Phe and Pro
Rationale: This is a Biochemistry question that falls under the content category
"Structure, function, and reactivity of biologically relevant molecules." The
peptide bond cleaved in Figure 1 is between phenylalanine and proline (Phe and
,Pro). This question requires Knowledge of Scientific Concepts and Principles,
specifically the knowledge of the structures of phenylalanine and proline, to arrive
at the answer.
Question 5
Which image best illustrates the electric field lines between the inside of an
axon and the surrounding extracellular solution?
A. Image A
B. Image B
C. Image C
D. Image D
Correct Answer: B. Image B
Rationale: This is a Physics question that falls under content category
"Electrochemistry and electrical circuits and their elements." The electric field
lines exit from positive and enter negative charges. The axon is negatively charged.
The extracellular solution has a zero net potential. It is a Knowledge of Scientific
Concepts and Principles question because the examinee must identify the
relationship between the distribution of electric charges in the axon and the
electric field lines they produce.
Question 6
What is the closest distance the electrodes used in an NCV test can be placed on
a nerve in order to measure the voltage change as a response to the stimulus?
A. 0.01 m
B. 0.1 m
C. 1.0 m
D. 10 m
Correct Answer: B. 0.1 m
Rationale: This is a Physics question that falls under content category
"Translational motion, forces, work, energy, and equilibrium in living systems." The
, shortest time duration that can be detected is not less than the action potential
time response of 1 msec, according to Figure 1. The distance travelled by the
impulse during this time is 1 msec × 100 m/s = 0.1 m, which is the closest distance
the electrodes must be placed on the nerve. This question requires Scientific
Reasoning and Problem-Solving, correct determination and use of a scientific
formula, in order to arrive at the answer.
Question 7
What was the pH of the unknown aqueous solution?
A. 4
B. 5
C. 9
D. 10
Correct Answer: B. 5
Rationale: This is a General Chemistry question that falls under the content
category "Unique nature of water and its solutions." The pH of the solution is, by
definition, –log([H⁺]). Since the hydrogen ion concentration for the unknown
aqueous solution was given as 1 × 10⁻⁵, the pH of this solution is 5. The passage
states: "The hydrogen ion concentration of the unknown aqueous solution was 1 ×
10⁻⁵ M." This question requires Scientific Reasoning and Problem Solving to arrive
at the answer.
Question 8
Two additional compounds were studied: NO₂(OH) dissolved in water and
produced an acidic solution, and Ni(OH)₂ dissolved only in an acidic solution.
What type of compounds were these?
A. Both were oxyacids.
B. Both were bases.
C. NO₂(OH) was a base and Ni(OH)₂ was an oxyacid.
D. NO₂(OH) was an oxyacid and Ni(OH)₂ was a base.
Correct Answers and Rationale | Graded A+ | New
2026-2027 Update
Question 1
Compound 1 is used to treat HIV infection based on its ability to act as:
A. an agonist.
B. an antagonist.
C. a placebo.
D. a catalyst.
Correct Answer: B. an antagonist.
Rationale: This is a Biochemistry question that falls under content category
"Principles of chemical thermodynamics and kinetics." Compound 1 binds to the
transition state of HIV protease and serves to treat infection. It is clearly inhibiting
this enzyme through its binding and thus serves as an antagonist. This question
requires Knowledge of Scientific Concepts and Principles, specifically the
definition of an antagonist, to arrive at the answer. The passage states: "One such
molecule is Compound 1, shown in Figure 2, which is a potent HIV protease
inhibitor."
Question 2
How many stereoisomers of Compound 1 exist?
A. 8
B. 16
C. 32
D. 64
Correct Answer: C. 32
,Rationale: This is an Organic Chemistry question that falls under the content
category "Nature of molecules and intermolecular interactions." There are 5
chirality centers in Compound 1. By application of the 2ⁿ rule, there are 2⁵ = 32
possible stereoisomers. This question requires Scientific Reasoning and Problem
Solving to arrive at the answer.
Question 3
Why do kidney stones form in some individuals treated with Compound 1?
A. [Ca²⁺] + [C₂O₄²⁻] > Ksp
B. [Ca²⁺][C₂O₄²⁻] > Ksp
C. [Ca²⁺] + [C₂O₄²⁻] < Ksp
D. [Ca²⁺][C₂O₄²⁻] < Ksp
Correct Answer: B. [Ca²⁺][C₂O₄²⁻] > Ksp
Rationale: This is a General Chemistry question that falls under the content
category "Unique nature of water and its solutions." Calcium oxalate precipitates
when [Ca²⁺][C₂O₄²⁻] exceeds the solubility product constant Ksp by definition. This
question requires Scientific Reasoning and Problem Solving to arrive at the
answer.
Question 4
The peptide bond between which two amino acid residues is cleaved by HIV
protease?
A. Phe and Ala
B. Pro and Val
C. Val and Ala
D. Phe and Pro
Correct Answer: D. Phe and Pro
Rationale: This is a Biochemistry question that falls under the content category
"Structure, function, and reactivity of biologically relevant molecules." The
peptide bond cleaved in Figure 1 is between phenylalanine and proline (Phe and
,Pro). This question requires Knowledge of Scientific Concepts and Principles,
specifically the knowledge of the structures of phenylalanine and proline, to arrive
at the answer.
Question 5
Which image best illustrates the electric field lines between the inside of an
axon and the surrounding extracellular solution?
A. Image A
B. Image B
C. Image C
D. Image D
Correct Answer: B. Image B
Rationale: This is a Physics question that falls under content category
"Electrochemistry and electrical circuits and their elements." The electric field
lines exit from positive and enter negative charges. The axon is negatively charged.
The extracellular solution has a zero net potential. It is a Knowledge of Scientific
Concepts and Principles question because the examinee must identify the
relationship between the distribution of electric charges in the axon and the
electric field lines they produce.
Question 6
What is the closest distance the electrodes used in an NCV test can be placed on
a nerve in order to measure the voltage change as a response to the stimulus?
A. 0.01 m
B. 0.1 m
C. 1.0 m
D. 10 m
Correct Answer: B. 0.1 m
Rationale: This is a Physics question that falls under content category
"Translational motion, forces, work, energy, and equilibrium in living systems." The
, shortest time duration that can be detected is not less than the action potential
time response of 1 msec, according to Figure 1. The distance travelled by the
impulse during this time is 1 msec × 100 m/s = 0.1 m, which is the closest distance
the electrodes must be placed on the nerve. This question requires Scientific
Reasoning and Problem-Solving, correct determination and use of a scientific
formula, in order to arrive at the answer.
Question 7
What was the pH of the unknown aqueous solution?
A. 4
B. 5
C. 9
D. 10
Correct Answer: B. 5
Rationale: This is a General Chemistry question that falls under the content
category "Unique nature of water and its solutions." The pH of the solution is, by
definition, –log([H⁺]). Since the hydrogen ion concentration for the unknown
aqueous solution was given as 1 × 10⁻⁵, the pH of this solution is 5. The passage
states: "The hydrogen ion concentration of the unknown aqueous solution was 1 ×
10⁻⁵ M." This question requires Scientific Reasoning and Problem Solving to arrive
at the answer.
Question 8
Two additional compounds were studied: NO₂(OH) dissolved in water and
produced an acidic solution, and Ni(OH)₂ dissolved only in an acidic solution.
What type of compounds were these?
A. Both were oxyacids.
B. Both were bases.
C. NO₂(OH) was a base and Ni(OH)₂ was an oxyacid.
D. NO₂(OH) was an oxyacid and Ni(OH)₂ was a base.
