AP-Micro Microbiology: Microbial Metabolism 3 β Questions and Answers
Question 1: A microorganism produces acetone and butanol as end products of fermentation. Which pathway is it most likely using?
- Homolactic fermentation
- Alcoholic fermentation
- Mixed acid fermentation
- Acetone-butanol-ethanol (ABE) fermentation (Correct answer)
Correct answer: Acetone-butanol-ethanol (ABE) fermentation
ABE fermentation is characteristic of Clostridium species, which produce acetone, butanol, and ethanol as major end products.
Question 2: Which of the following best describes anoxygenic photosynthesis in purple sulfur bacteria?
- Uses water as electron donor, releases O2
- Uses H2S as electron donor, releases sulfur, no O2 produced (Correct answer)
- Uses CO2 as electron donor, releases glucose
- Uses glucose as electron donor, releases CO2
Correct answer: Uses H2S as electron donor, releases sulfur, no O2 produced
Purple sulfur bacteria use H2S as their electron donor, depositing elemental sulfur, and do not produce oxygen as a byproduct.
Question 3: The Entner-Doudoroff (ED) pathway produces which net products per glucose (compared to glycolysis)?
- 4 ATP, 2 NADH, 2 pyruvate
- 1 ATP, 1 NADH, 1 NADPH, 2 pyruvate (Correct answer)
- 2 ATP, 2 NADH, 2 pyruvate
- 3 ATP, 3 NADH, 2 pyruvate
Correct answer: 1 ATP, 1 NADH, 1 NADPH, 2 pyruvate
The ED pathway yields only 1 ATP, 1 NADH, and 1 NADPH per glucose while still producing 2 pyruvate molecules.
Question 4: Catabolite repression in E. coli ensures that glucose is preferentially metabolized over lactose primarily through:
- High cAMP levels activating the lac operon
- Low cAMP levels preventing CAP activation of the lac operon (Correct answer)
- High lactose concentrations inhibiting glucose uptake
- Constitutive expression of Ξ²-galactosidase
Correct answer: Low cAMP levels preventing CAP activation of the lac operon
When glucose is present, adenylyl cyclase activity is low, keeping cAMP levels low so CAP cannot activate the lac operon.
Question 5: During beta-oxidation of a 16-carbon saturated fatty acid, how many acetyl-CoA molecules are produced?
- 6
- 7
- 8 (Correct answer)
- 16
Correct answer: 8
A 16-carbon fatty acid undergoes 7 rounds of beta-oxidation to yield 8 acetyl-CoA, 7 NADH, and 7 FADH2.
Question 6: Which enzyme catalyzes the committed step of the pentose phosphate pathway?
- Phosphofructokinase
- Glucose-6-phosphate dehydrogenase (Correct answer)
- Hexokinase
- Transketolase
Correct answer: Glucose-6-phosphate dehydrogenase
Glucose-6-phosphate dehydrogenase oxidizes glucose-6-phosphate to 6-phosphogluconolactone, committing the molecule to the pentose phosphate pathway.
Question 7: What type of metabolism does an organism exhibit if it can grow under both aerobic and anaerobic conditions but grows more efficiently with oxygen?
- Obligate aerobe
- Obligate anaerobe
- Facultative anaerobe (Correct answer)
- Microaerophile
Correct answer: Facultative anaerobe
Facultative anaerobes can perform both aerobic respiration and fermentation/anaerobic respiration, but prefer oxygen for its higher ATP yield.
AP-Micro Microbiology: Microbial Metabolism 3
A microorganism produces acetone and butanol as end products of fermentation.
Which pathway is it most likely using?