Questions on the Krebs Cycle
20 multiple-choice questions about the Krebs Cycle with five alternatives each. Answers are at the end.
Multiple Choice Questions: Krebs Cycle
1. Where does the Krebs cycle take place in the cell?
A) Cytoplasm
B) Mitochondrial matrix
C) Outer mitochondrial membrane
D) Nucleus
E) Golgi apparatus
2. What is the first molecule that enters the Krebs cycle?
A) Pyruvate
B) Acetyl-CoA
C) Oxaloacetate
D) Citrate
E) Fumarate
3. Acetyl-CoA combines with which molecule to start the Krebs cycle?
A) Citrate
B) Oxaloacetate
C) Malate
D) Succinate
E) Fumarate
4. How many carbon atoms does acetyl-CoA contribute to the Krebs cycle?
A) 1
B) 2
C) 3
D) 4
E) 6
5. Which molecule is produced after acetyl-CoA combines with oxaloacetate?
A) Succinate
B) Citrate
C) Malate
D) Fumarate
E) Alpha-ketoglutarate
6. How many ATP (or GTP) molecules are produced per turn of the Krebs cycle?
A) 1
B) 2
C) 3
D) 4
E) 6
7. How many NADH molecules are produced in one turn of the Krebs cycle?
A) 1
B) 2
C) 3
D) 4
E) 5
8. How many FADH₂ molecules are produced per turn of the Krebs cycle?
A) 1
B) 2
C) 3
D) 4
E) 5
9. Which molecule is regenerated at the end of the Krebs cycle to combine with acetyl-CoA again?
A) Succinate
B) Malate
C) Oxaloacetate
D) Citrate
E) Fumarate
10. Which molecule leaves the Krebs cycle as a waste product?
A) Oxygen
B) Carbon dioxide
C) Water
D) Nitrogen
E) ATP
11. Which enzyme catalyzes the conversion of citrate to isocitrate?
A) Citrate synthase
B) Aconitase
C) Isocitrate dehydrogenase
D) Succinyl-CoA synthetase
E) Malate dehydrogenase
12. Which step of the Krebs cycle produces the first molecule of CO₂?
A) Acetyl-CoA combining with oxaloacetate
B) Isocitrate converting to alpha-ketoglutarate
C) Succinate converting to fumarate
D) Malate converting to oxaloacetate
E) Citrate converting to isocitrate
13. Which enzyme converts alpha-ketoglutarate to succinyl-CoA?
A) Alpha-ketoglutarate dehydrogenase
B) Succinyl-CoA synthetase
C) Succinate dehydrogenase
D) Fumarase
E) Malate dehydrogenase
14. What type of phosphorylation occurs during the Krebs cycle?
A) Oxidative phosphorylation
B) Substrate-level phosphorylation
C) Photophosphorylation
D) Chemiosmosis
E) None
15. Which complex in the electron transport chain accepts electrons from FADH₂ produced in the Krebs cycle?
A) Complex I
B) Complex II
C) Complex III
D) Complex IV
E) ATP synthase
16. What is the total number of carbon dioxide molecules released per glucose molecule after two turns of the Krebs cycle?
A) 2
B) 3
C) 4
D) 6
E) 8
17. Which molecule acts as an electron carrier in the Krebs cycle?
A) ATP
B) NAD+
C) FAD
D) Both B and C
E) ADP
18. Which molecule is converted to malate during the Krebs cycle?
A) Succinate
B) Fumarate
C) Citrate
D) Oxaloacetate
E) Alpha-ketoglutarate
19. What is the role of succinate dehydrogenase in the Krebs cycle?
A) Converts succinate to fumarate and reduces FAD to FADH₂
B) Converts malate to oxaloacetate
C) Converts citrate to isocitrate
D) Converts alpha-ketoglutarate to succinyl-CoA
E) Converts isocitrate to alpha-ketoglutarate
20. The Krebs cycle is also known as:
A) Calvin cycle
B) Citric acid cycle
C) Glycolysis
D) Electron transport chain
E) Fermentation
Answer Key
1. B
2. B
3. B
4. B
5. B
6. A
7. C
8. A
9. C
10. B
11. B
12. B
13. A
14. B
15. B
16. D
17. D
18. B
19. A
20. B
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