DAT Biology: Cellular Metabolism 3 — Questions and Answers
Question 1: The pyruvate dehydrogenase complex converts pyruvate into which molecule entering the citric acid cycle?
- Acetyl-CoA (Correct answer)
- Citrate
- Lactate
- Oxaloacetate
Correct answer: Acetyl-CoA
Pyruvate is oxidatively decarboxylated to acetyl-CoA, releasing CO2 and producing NADH.
Question 2: How many CO2 molecules are released per turn of the citric acid cycle?
- 2 (Correct answer)
- 1
- 3
- 4
Correct answer: 2
Isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase each release one CO2 per turn.
Question 3: Which molecule combines with acetyl-CoA to form citrate?
- Oxaloacetate (Correct answer)
- Malate
- Succinate
- Fumarate
Correct answer: Oxaloacetate
Citrate synthase condenses acetyl-CoA with oxaloacetate to begin the cycle.
Question 4: Per turn of the citric acid cycle, how many NADH molecules are produced?
- 3 (Correct answer)
- 1
- 2
- 4
Correct answer: 3
Three NADH are generated at the isocitrate, alpha-ketoglutarate, and malate dehydrogenase steps.
Question 5: Which high-energy molecule is produced directly by substrate-level phosphorylation in the citric acid cycle?
- GTP (Correct answer)
- ATP
- NADPH
- FADH2
Correct answer: GTP
Succinyl-CoA synthetase produces GTP (or ATP) by substrate-level phosphorylation.
Question 6: In which cellular compartment does the citric acid cycle occur?
- Mitochondrial matrix (Correct answer)
- Cytoplasm
- Inner mitochondrial membrane
- Intermembrane space
Correct answer: Mitochondrial matrix
All citric acid cycle enzymes reside in the mitochondrial matrix, except succinate dehydrogenase.
Question 7: Which citric acid cycle enzyme is also a component of the electron transport chain (Complex II)?
- Succinate dehydrogenase (Correct answer)
- Citrate synthase
- Aconitase
- Fumarase
Correct answer: Succinate dehydrogenase
Succinate dehydrogenase is embedded in the inner membrane and feeds FADH2 electrons directly into Complex II.
DAT Biology: Cellular Metabolism 3
The pyruvate dehydrogenase complex converts pyruvate into which molecule entering the citric acid cycle?