CHEM 210 Biochemistry Module 7 Exam - Citric Acid Cycle, ETC, and
Oxidative Phosphorylation 2026/2027 UPDATE
1. In which part of the mitochondria does the Citric Acid Cycle (CAC) primarily
occur?
A. Outer membrane
B. Intermembrane space
C. Mitochondrial matrix
D. Inner membrane
Answer: C
Rationale: The enzymes of the Citric Acid Cycle are located within the mitochondrial
matrix, except for succinate dehydrogenase, which is bound to the inner membrane.
2. Which molecule acts as the starting point of the Citric Acid Cycle by reacting
with oxaloacetate?
A. Acetyl-CoA
B. Pyruvate
C. Citrate
D. Malate
Answer: A
Rationale: Acetyl-CoA condenses with oxaloacetate to form citrate, catalyzed by the
enzyme citrate synthase.
,3. How many molecules of NADH are produced per single turn of the Citric Acid
Cycle?
A. 1
B. 2
C. 3
D. 4
Answer: C
Rationale: One turn of the CAC produces three NADH molecules at the steps catalyzed by
isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, and malate dehydrogenase.
4. Which enzyme in the Citric Acid Cycle is also considered Complex II of the
Electron Transport Chain?
A. Citrate synthase
B. Isocitrate dehydrogenase
C. Succinate dehydrogenase
D. Fumarase
Answer: C
Rationale: Succinate dehydrogenase is the only enzyme of the CAC that is embedded in the
inner mitochondrial membrane, doubling as Complex II of the ETC.
5. What is the primary role of the Electron Transport Chain?
A. To produce CO2 for the lungs
B. To synthesize glucose from pyruvate
C. To create a proton gradient across the inner membrane
D. To break down ATP into ADP
Answer: C
Rationale: The ETC uses the energy from electron transfers to pump protons into the
intermembrane space, creating an electrochemical gradient.
, 6. Which complex of the Electron Transport Chain does NOT pump protons
across the inner mitochondrial membrane?
A. Complex I
B. Complex II
C. Complex III
D. Complex IV
Answer: B
Rationale: Complex II (succinate dehydrogenase) transfers electrons from FADH2 to
Coenzyme Q but does not have the energy required to pump protons.
7. What is the final electron acceptor in the Electron Transport Chain?
A. NAD+
B. FAD
C. Water (H2O)
D. Oxygen (O2)
Answer: D
Rationale: Oxygen is the terminal electron acceptor, where it is reduced to form water at
Complex IV.
8. The F0 domain of ATP Synthase is responsible for which of the following?
A. Binding ADP and Pi
B. Catalyzing the synthesis of ATP
C. Acting as a proton channel
D. Releasing ATP into the matrix
Answer: C
Rationale: The F0 domain is the membrane-embedded portion that allows protons to flow
back into the matrix.
Oxidative Phosphorylation 2026/2027 UPDATE
1. In which part of the mitochondria does the Citric Acid Cycle (CAC) primarily
occur?
A. Outer membrane
B. Intermembrane space
C. Mitochondrial matrix
D. Inner membrane
Answer: C
Rationale: The enzymes of the Citric Acid Cycle are located within the mitochondrial
matrix, except for succinate dehydrogenase, which is bound to the inner membrane.
2. Which molecule acts as the starting point of the Citric Acid Cycle by reacting
with oxaloacetate?
A. Acetyl-CoA
B. Pyruvate
C. Citrate
D. Malate
Answer: A
Rationale: Acetyl-CoA condenses with oxaloacetate to form citrate, catalyzed by the
enzyme citrate synthase.
,3. How many molecules of NADH are produced per single turn of the Citric Acid
Cycle?
A. 1
B. 2
C. 3
D. 4
Answer: C
Rationale: One turn of the CAC produces three NADH molecules at the steps catalyzed by
isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, and malate dehydrogenase.
4. Which enzyme in the Citric Acid Cycle is also considered Complex II of the
Electron Transport Chain?
A. Citrate synthase
B. Isocitrate dehydrogenase
C. Succinate dehydrogenase
D. Fumarase
Answer: C
Rationale: Succinate dehydrogenase is the only enzyme of the CAC that is embedded in the
inner mitochondrial membrane, doubling as Complex II of the ETC.
5. What is the primary role of the Electron Transport Chain?
A. To produce CO2 for the lungs
B. To synthesize glucose from pyruvate
C. To create a proton gradient across the inner membrane
D. To break down ATP into ADP
Answer: C
Rationale: The ETC uses the energy from electron transfers to pump protons into the
intermembrane space, creating an electrochemical gradient.
, 6. Which complex of the Electron Transport Chain does NOT pump protons
across the inner mitochondrial membrane?
A. Complex I
B. Complex II
C. Complex III
D. Complex IV
Answer: B
Rationale: Complex II (succinate dehydrogenase) transfers electrons from FADH2 to
Coenzyme Q but does not have the energy required to pump protons.
7. What is the final electron acceptor in the Electron Transport Chain?
A. NAD+
B. FAD
C. Water (H2O)
D. Oxygen (O2)
Answer: D
Rationale: Oxygen is the terminal electron acceptor, where it is reduced to form water at
Complex IV.
8. The F0 domain of ATP Synthase is responsible for which of the following?
A. Binding ADP and Pi
B. Catalyzing the synthesis of ATP
C. Acting as a proton channel
D. Releasing ATP into the matrix
Answer: C
Rationale: The F0 domain is the membrane-embedded portion that allows protons to flow
back into the matrix.
