Question 1

Which enzyme catalyzes the phosphorylation of glucose in the first step of glycolysis, and what is the significance of this reaction?

Accepted Answer

Hexokinase; it traps glucose inside the cell by converting it to glucose-6-phosphate.

Question 2

During glycolysis, which step is considered the main regulatory and rate-limiting step, and what molecule is produced as a result?

Accepted Answer

Step 3: Phosphorylation of fructose-6-phosphate by phosphofructokinase-1; fructose 1,6-bisphosphate

Question 3

Which of the following best describes substrate-level phosphorylation, and in which steps of glycolysis does it occur?

Accepted Answer

It is the direct transfer of a phosphate group to ADP from a phosphorylated intermediate; it occurs in steps 7 and 10.

Question 4

A mutation in the gene encoding triose phosphate isomerase would most directly affect which step of glycolysis, and what would be the likely consequence?

Accepted Answer

Step 5; accumulation of dihydroxyacetone phosphate and reduced ATP yield

Question 5

Which of the following statements about the fate of pyruvate is CORRECT?

Accepted Answer

In the presence of oxygen, pyruvate is converted to acetyl-CoA and enters the citric acid cycle.

Question 6

In prokaryotic cells, where do the reactions of the citric acid cycle and pyruvate oxidation occur?

Accepted Answer

In the cytoplasm

Question 7

Which of the following is a direct product of the citric acid cycle per one acetyl-CoA molecule?

Accepted Answer

$$3$$ NADH, $$1$$ FADH$$_2$$, $$1$$ ATP (or GTP), $$2 CO$_2$$

Question 8

Which enzyme catalyzes the conversion of succinate to fumarate in the citric acid cycle, and what is the associated electron carrier?

Accepted Answer

Succinate dehydrogenase; FAD is reduced to FADH$$_2$$

Question 9

Which of the following best explains why glycolysis is considered an anaerobic process?

Accepted Answer

It does not require oxygen to proceed and can occur in both aerobic and anaerobic conditions.

Question 10

Gut microbes ferment dietary fiber to produce short-chain fatty acids (SCFAs). Which SCFA is most directly associated with anti-inflammatory effects in the immune system?

Accepted Answer

Butyrate

Question 11

Which of the following is a key effect of butyrate on the nervous system?

Accepted Answer

It enhances the integrity of the blood-brain barrier.

Question 12

A patient has a deficiency in phosphofructokinase-1 (PFK-1). Which step of glycolysis is directly impaired, and what is the consequence for ATP production?

Accepted Answer

Step 3; fructose-6-phosphate cannot be converted to fructose 1,6-bisphosphate, reducing glycolytic flux and ATP yield.

Question 13

Which of the following best describes the role of exoenzymes in microbial carbohydrate metabolism?

Accepted Answer

They break down complex carbohydrates outside the cell into smaller sugars for uptake.

Question 14

Which metabolic pathway is responsible for the conversion of tryptophan into indoles by gut microbes, and what is the immunological significance of these indoles?

Accepted Answer

Tryptophan catabolism; indoles interact with the aryl hydrocarbon receptor (Ahr) to regulate immune responses.

Question 15

Which of the following is NOT a product of glycolysis per molecule of glucose?

Accepted Answer

$$4$$ $$CO_2$

Question 16

If a microbe is unable to produce exoenzymes, which of the following would most likely occur?

Accepted Answer

It would be unable to digest and utilize complex carbohydrates like cellulose or starch.

Question 17

Which step in the citric acid cycle directly produces GTP (or ATP) via substrate-level phosphorylation?

Accepted Answer

Conversion of succinyl-CoA to succinate

Question 18

Which of the following best explains the importance of the gut-brain axis in microbial metabolism?

Accepted Answer

Microbial metabolites can influence brain function via the vagus nerve and blood-brain barrier integrity.

Microbial Metabolism II: Glycolysis, Citric Acid Cycle, and Microbial Metabolites

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