AP-Micro Microbiology: Microbial Metabolism 2 — Questions and Answers
Question 1: Which enzyme complex is responsible for pumping protons across the inner mitochondrial or bacterial membrane during electron transport?
- ATP synthase
- NADH dehydrogenase (Complex I) (Correct answer)
- Pyruvate dehydrogenase
- Isocitrate dehydrogenase
Correct answer: NADH dehydrogenase (Complex I)
NADH dehydrogenase (Complex I) oxidizes NADH and pumps protons across the membrane, contributing to the proton motive force.
Question 2: What is the net ATP yield from substrate-level phosphorylation during glycolysis alone (per glucose)?
- 4 ATP
- 2 ATP (Correct answer)
- 1 ATP
- 38 ATP
Correct answer: 2 ATP
Glycolysis produces 4 ATP but consumes 2 ATP for a net yield of 2 ATP via substrate-level phosphorylation.
Question 3: A bacterium living in a deep-sea hydrothermal vent uses H2S as an electron donor to fix CO2. This organism is best classified as a:
- Photoautotroph
- Chemoautotroph (lithotroph) (Correct answer)
- Chemoheterotroph
- Photoheterotroph
Correct answer: Chemoautotroph (lithotroph)
Chemoautotrophs (lithotrophs) obtain energy from inorganic compounds like H2S and use CO2 as a carbon source.
Question 4: During the citric acid cycle, how many NADH molecules are produced per acetyl-CoA entering?
- 2
- 3 (Correct answer)
- 4
- 6
Correct answer: 3
Three NADH molecules are generated per acetyl-CoA in the TCA cycle at isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, and malate dehydrogenase.
Question 5: Which metabolic process directly produces FADH2 in the TCA cycle?
- Isocitrate → alpha-ketoglutarate
- Malate → oxaloacetate
- Succinate → fumarate (Correct answer)
- Citrate → isocitrate
Correct answer: Succinate → fumarate
Succinate dehydrogenase oxidizes succinate to fumarate using FAD as the electron acceptor, generating FADH2.
Question 6: What is the primary role of fermentation in microbial metabolism?
- To generate the majority of ATP from glucose
- To regenerate NAD+ so glycolysis can continue (Correct answer)
- To fix atmospheric nitrogen
- To synthesize amino acids from pyruvate
Correct answer: To regenerate NAD+ so glycolysis can continue
Fermentation regenerates NAD+ by transferring electrons from NADH to organic molecules, allowing glycolysis to continue producing ATP.
Question 7: Which compound serves as the final electron acceptor in aerobic respiration?
- NAD+
- Pyruvate
- Molecular oxygen (O2) (Correct answer)
- Sulfate (SO4²⁻)
Correct answer: Molecular oxygen (O2)
In aerobic respiration, O2 is the terminal electron acceptor and is reduced to water by cytochrome c oxidase (Complex IV).
AP-Micro Microbiology: Microbial Metabolism 2
Which enzyme complex is responsible for pumping protons across the inner mitochondrial or bacterial membrane during electron transport?