9.4 Microbial Physiology Module 9: Metabolism

Which of the following reactions is involved in the conversion of pyruvate to acetyl coenzyme A?

• oxidative phosphorylation

• oxidative deamination

• oxidative decarboxylation

• oxidative transamination

Answer explanation

Answer: c. oxidative decarboxylation. Pyruvate undergoes oxidative decarboxylation, producing acetyl-CoA, CO₂, and NADH

Reference:

Brock et al., 2021

Which of the following gases is a by-product of the reaction between pyruvate and coenzyme A?

• CO

• CO₂

• O₂

• none of these

Answer explanation

Answer: b. CO₂. Carbon dioxide is a by-product of the oxidative decarboxylation of pyruvate

References:

Brock et al., 2021

Struck & White, 2019

Which of the following carbohydrates cannot enter the glycolytic pathway?

• Fructose

• Galactose

• Glycogen

• None of these

Answer explanation

Answer: c. glycogen. Glycogen must first be broken down into glucose or glucose-6-phosphate

Reference:

Blanco, A., & Blanco, G. (2017). Carbohydrate metabolism. In Elsevier eBooks (pp. 283–323). https://doi.org/10.1016/b978-0-12-803550-4.00014-8

Struck & White, 2019

Which of the following compounds is required to convert glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate?

• ADP

• ATP

• NADH

• NAD+

Answer explanation

Answer: d. NAD⁺. NAD² is reduced to NADH in this oxidation step

References:

Blanco, A., & Blanco, G. (2017). Carbohydrate metabolism. In Elsevier eBooks (pp. 283–323). https://doi.org/10.1016/b978-0-12-803550-4.00014-8

Brock et al., 2021

How many molecules of FADH2 are obtained for each acetyl CoA molecule that enters the common catabolic pathway?

• 1

• 2

• 3

• 4

Answer explanation

Answer: a. 1. One FADH₂ is generated for each acetyl-CoA oxidized in the citric acid cycle

Reference:

(Struck & White, 2019).

How many molecules of ATP are produced during the conversion of two molecules of 1,3-bisphosphoglycerate to yield two molecules of pyruvate?

• 2

• 4

• 6

• 12

Answer explanation

Answer: b. 4. Two ATP molecules are generated per 1,3-bisphosphoglycerate via substrate-level phosphorylation

References:

Struck & White, 2019

https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/glycolysis/a/glycolysis

Which of the following acts as the oxidizing agent in the conversion of pyruvate to acetyl coenzyme A?

• ATP

• NAD+

• NADH

• Pyruvate

Answer explanation

Answer: b. NAD⁺. NAD⁺ accepts electrons, becoming NADH

References:

Struck & White, 2019

https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/General_Biology_(Boundless)/07%3A_Cellular_Respiration/7.08%3A_Oxidation_of_Pyruvate_and_the_Citric_Acid_Cycle_-__Breakdown_of_Pyruvate#:~:text=The%20conversion%20of%20pyruvate%20to,CoA%20to%20produce%20Acetyl%20CoA.

Which of the following gases is a by-product of the reaction between pyruvate and coenzyme A?

• CO

• CO₂

• O₂

• none of these

Answer explanation

Answer: b. CO₂. CO₂ is a by-product of this reaction

Reference:

Brock et al., 2021

Which of the following statements is true of anaerobic reactions?

• They are all redox reactions.

• They are all oxidation reactions.

• They occur in the presence of oxygen.

• They occur in the absence of oxygen.

Answer explanation

Answer: d. They occur in the absence of oxygen. Anaerobic reactions proceed without oxygen, producing less ATP than aerobic pathways

References:

Struck & White, 2019

What is the effect of excess ATP on glycolysis?

• It enhances the rate of glycolysis.

• It moderately reduces the rate of glycolysis.

• It shuts down glycolysis.

• It has no effect on glycolysis.

Answer explanation

Answer: b. It moderately reduces the rate of glycolysis. ATP acts as an allosteric inhibitor of the key regulatory enzyme of glycolysis, Phosphofructokinase-1 (PFK-1). When the cell has excess ATP (high energy charge), ATP binds to an allosteric site on PFK-1, lowering its affinity for its substrate and thus reducing the rate of glycolysis. It does not typically "shut down" the pathway entirely, but rather slows it down to conserve glucose until the ATP is consumed.

Reference:

Brock et al., 2021