Question 1

Which of the following statements best describes the role of NAD+ in glycolysis?

Accepted Answer

NAD+ is reduced during glycolysis, accepting electrons from glyceraldehyde-3-phosphate.

Question 2

During the preparatory phase of glycolysis, which step is thermodynamically driven by ATP hydrolysis, and what is the equation for ATP hydrolysis?

Accepted Answer

The conversion of fructose-6-phosphate to fructose-1,6-bisphosphate; $$\mathrm{ATP} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{ADP} + \mathrm{P}_i$$

Question 3

Which intermediate in glycolysis is stabilized by acid/base catalysis involving the formation of an enolate?

Accepted Answer

Phosphoenolpyruvate

Question 4

In the conversion of pyruvate to acetyl-CoA by the pyruvate dehydrogenase complex, which cofactor is directly involved in the decarboxylation of pyruvate?

Accepted Answer

Thiamine pyrophosphate (TPP)

Question 5

Which of the following reactions in glycolysis is reversible under cellular conditions?

Accepted Answer

Aldolase: fructose-1,6-bisphosphate to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate

Question 6

Which statement best explains why fermentation is necessary in anaerobic conditions?

Accepted Answer

Fermentation recycles NAD+ required for glycolysis to continue.

Question 7

Which of the following best describes the fate of the two carbons from acetyl-CoA in the TCA cycle?

Accepted Answer

Neither carbon is released as CO$$_2 in $$the first turn; they remain in the cycle.

Question 8

Which mechanism is shared between the pyruvate dehydrogenase complex and the alpha-ketoglutarate dehydrogenase complex in the TCA cycle?

Accepted Answer

Decarboxylation using thiamine pyrophosphate (TPP) and reduction of lipoate

Question 9

Which of the following is a correct description of the mechanism of glycogen phosphorylase?

Accepted Answer

It removes glucose units from glycogen by phosphorolysis, producing glucose-1-phosphate.

Question 10

Which of the following best explains the thermodynamic logic of coupling reactions in glycolysis?

Accepted Answer

Coupling endergonic reactions to exergonic reactions allows the overall process to proceed spontaneously.

Question 11

During ethanol fermentation, which enzyme catalyzes the reduction of acetaldehyde to ethanol, and what is the associated redox reaction?

Accepted Answer

Alcohol dehydrogenase; $$\mathrm{CH}_3\mathrm{CHO} + \mathrm{NADH} + H^+ \rightarrow \mathrm{C}_2\mathrm{H}_5\mathrm{OH} + \mathrm{NAD}^+$$

Question 12

Which of the following is NOT a key intermediate formed via aldol or enolate chemistry in glycolysis?

Accepted Answer

Glucose-6-phosphate

Question 13

Which step in gluconeogenesis bypasses an irreversible step in glycolysis, and what is the equation for this reaction?

Accepted Answer

Conversion of pyruvate to phosphoenolpyruvate via oxaloacetate; $$\mathrm{Pyruvate} + \mathrm{CO}_2 + \mathrm{ATP} \rightarrow \mathrm{Oxaloacetate} + \mathrm{ADP} + \mathrm{P}_i$$

Question 14

Which of the following best describes the role of lipoate in the pyruvate dehydrogenase complex?

Accepted Answer

Lipoate acts as a carrier of acetyl groups and is reduced during the transfer of electrons.

Question 15

Which of the following statements about the cyclic nature of the TCA cycle is correct?

Accepted Answer

The cycle regenerates oxaloacetate, allowing continuous processing of acetyl-CoA.

Question 16

Which of the following is a correct description of the mechanism of citrate synthase in the TCA cycle?

Accepted Answer

Citrate synthase catalyzes the condensation of acetyl-CoA and oxaloacetate to form citrate via a Claisen condensation.

Question 17

A patient with a deficiency in thiamine (vitamin B$$_1) $$would most likely have impaired activity in which of the following enzymes?

Accepted Answer

Pyruvate dehydrogenase

Question 18

Which of the following best explains why gluconeogenesis is not simply the reverse of glycolysis?

Accepted Answer

Three steps in glycolysis are highly exergonic and must be bypassed by different enzymes in gluconeogenesis.

Question 19

Which of the following is a key reason why fermentation is considered inefficient compared to aerobic respiration?

Accepted Answer

Fermentation produces less ATP per glucose molecule because it does not fully oxidize glucose to CO$$_2.$$

Glycolysis, Gluconeogenesis, Fermentation, Pyruvate Dehydrogenase, and TCA Cycle: Study Guide

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