CHEM 210 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 primarily occur?
A. Intermembrane space
B. Mitochondrial matrix
C. Outer membrane
D. Inner membrane
Answer: B
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 enzyme catalyzes the conversion of pyruvate to acetyl-CoA?
A. Pyruvate kinase
B. Pyruvate dehydrogenase complex
C. Aconitase
D. Citrate synthase
Answer: B
Rationale: The Pyruvate Dehydrogenase Complex (PDC) is responsible for the oxidative
decarboxylation of pyruvate into acetyl-CoA.
,3. What are the three products of the Pyruvate Dehydrogenase Complex
reaction?
A. Citrate, NADH, and O2
B. Acetyl-CoA, FADH2, and CO2
C. Pyruvate, ATP, and NADH
D. Acetyl-CoA, NADH, and CO2
Answer: D
Rationale: The conversion of pyruvate to acetyl-CoA produces one molecule of NADH and
releases one molecule of CO2.
4. Which molecule condenses with oxaloacetate to form citrate in the first step
of the Citric Acid Cycle?
A. Succinyl-CoA
B. Pyruvate
C. Malate
D. Acetyl-CoA
Answer: D
Rationale: Citrate synthase catalyzes the condensation of the two-carbon acetyl group
from acetyl-CoA with the four-carbon oxaloacetate.
5. How many molecules of NADH are produced during one single turn of the
Citric Acid Cycle?
A. 3
B. 2
C. 1
D. 4
Answer: A
Rationale: One turn of the cycle produces three NADH molecules at the isocitrate
dehydrogenase, alpha-ketoglutarate dehydrogenase, and malate dehydrogenase steps.
, 6. Which enzyme in the Citric Acid Cycle is also a component of the Electron
Transport Chain (Complex II)?
A. Isocitrate dehydrogenase
B. Fumarase
C. Succinate dehydrogenase
D. Malate dehydrogenase
Answer: C
Rationale: Succinate dehydrogenase is unique because it is embedded in the inner
mitochondrial membrane and functions in both the TCA cycle and the ETC.
7. What is the primary role of the Electron Transport Chain?
A. To produce glucose from CO2
B. To create a proton gradient across the inner mitochondrial membrane
C. To synthesize pyruvate from lactate
D. To break down ATP into ADP
Answer: B
Rationale: The ETC uses the energy from electron transfer to pump protons from the
matrix to the intermembrane space, creating an electrochemical gradient.
8. Which of the following is the final electron acceptor in the Electron Transport
Chain?
A. Oxygen
B. Carbon dioxide
C. Water
D. NAD+
Answer: A
Rationale: Oxygen (O2) is the final electron acceptor, which is reduced to form water
(H2O) at Complex IV.
Phosphorylation 2026/2027 UPDATE
1. In which part of the mitochondria does the Citric Acid Cycle primarily occur?
A. Intermembrane space
B. Mitochondrial matrix
C. Outer membrane
D. Inner membrane
Answer: B
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 enzyme catalyzes the conversion of pyruvate to acetyl-CoA?
A. Pyruvate kinase
B. Pyruvate dehydrogenase complex
C. Aconitase
D. Citrate synthase
Answer: B
Rationale: The Pyruvate Dehydrogenase Complex (PDC) is responsible for the oxidative
decarboxylation of pyruvate into acetyl-CoA.
,3. What are the three products of the Pyruvate Dehydrogenase Complex
reaction?
A. Citrate, NADH, and O2
B. Acetyl-CoA, FADH2, and CO2
C. Pyruvate, ATP, and NADH
D. Acetyl-CoA, NADH, and CO2
Answer: D
Rationale: The conversion of pyruvate to acetyl-CoA produces one molecule of NADH and
releases one molecule of CO2.
4. Which molecule condenses with oxaloacetate to form citrate in the first step
of the Citric Acid Cycle?
A. Succinyl-CoA
B. Pyruvate
C. Malate
D. Acetyl-CoA
Answer: D
Rationale: Citrate synthase catalyzes the condensation of the two-carbon acetyl group
from acetyl-CoA with the four-carbon oxaloacetate.
5. How many molecules of NADH are produced during one single turn of the
Citric Acid Cycle?
A. 3
B. 2
C. 1
D. 4
Answer: A
Rationale: One turn of the cycle produces three NADH molecules at the isocitrate
dehydrogenase, alpha-ketoglutarate dehydrogenase, and malate dehydrogenase steps.
, 6. Which enzyme in the Citric Acid Cycle is also a component of the Electron
Transport Chain (Complex II)?
A. Isocitrate dehydrogenase
B. Fumarase
C. Succinate dehydrogenase
D. Malate dehydrogenase
Answer: C
Rationale: Succinate dehydrogenase is unique because it is embedded in the inner
mitochondrial membrane and functions in both the TCA cycle and the ETC.
7. What is the primary role of the Electron Transport Chain?
A. To produce glucose from CO2
B. To create a proton gradient across the inner mitochondrial membrane
C. To synthesize pyruvate from lactate
D. To break down ATP into ADP
Answer: B
Rationale: The ETC uses the energy from electron transfer to pump protons from the
matrix to the intermembrane space, creating an electrochemical gradient.
8. Which of the following is the final electron acceptor in the Electron Transport
Chain?
A. Oxygen
B. Carbon dioxide
C. Water
D. NAD+
Answer: A
Rationale: Oxygen (O2) is the final electron acceptor, which is reduced to form water
(H2O) at Complex IV.
