Question 1

Which of the following best describes the role of phosphofructokinase-1 (PFK-1) in glycolysis?

Accepted Answer

PFK-1 catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate, using ATP.

Question 2

A patient with a deficiency in the pyruvate dehydrogenase complex (PDC) is likely to experience which of the following metabolic consequences?

Accepted Answer

Accumulation of lactic acid due to impaired entry of pyruvate into the TCA cycle.

Question 3

Which of the following is a feedforward activator of pyruvate kinase in glycolysis?

Accepted Answer

Fructose-1,6-bisphosphate

Question 4

During anaerobic glycolysis, what is the primary fate of pyruvate in human muscle cells?

Accepted Answer

It is converted to lactate to regenerate NAD$$^+.$$

Question 5

Which enzyme is responsible for catalyzing the irreversible step of glycolysis that commits glucose to the pathway?

Accepted Answer

Hexokinase or glucokinase

Question 6

A patient has a mutation that inactivates the malate-aspartate shuttle. Which of the following would most likely be observed?

Accepted Answer

Decreased transfer of cytosolic NADH electrons into the mitochondria, reducing ATP yield from glycolysis.

Question 7

Which of the following best explains why glucokinase is more active in the liver than hexokinase?

Accepted Answer

Glucokinase has a higher Km for glucose, allowing the liver to store glucose as glycogen when blood glucose is high.

Question 8

Which of the following allosteric effectors inhibits phosphofructokinase-1 (PFK-1) activity?

Accepted Answer

Citrate

Question 9

In the TCA cycle, which enzyme is physiologically unidirectional and is inhibited by arsenic?

Accepted Answer

Alpha-ketoglutarate dehydrogenase

Question 10

Which of the following best describes the function of the glycerol-3-phosphate shuttle?

Accepted Answer

It transfers reducing equivalents from cytosolic NADH to mitochondrial FAD, generating FADH$$_2$$ for the electron transport chain.

Question 11

A patient is found to have a deficiency in thiamine (vitamin B1). Which enzyme complex in the TCA cycle would be most directly affected?

Accepted Answer

Pyruvate dehydrogenase complex

Question 12

Which of the following statements about the regulation of glycolysis is correct?

Accepted Answer

High levels of ATP inhibit phosphofructokinase-1 (PFK-1) activity.

Question 13

Which of the following is a direct product of the pyruvate dehydrogenase complex (PDC) reaction?

Accepted Answer

Acetyl-CoA

Question 14

In the context of the TCA cycle, which cofactor is required by both the pyruvate dehydrogenase complex and alpha-ketoglutarate dehydrogenase?

Accepted Answer

Thiamine (vitamin B1)

Question 15

Which of the following best explains why oxaloacetate cannot cross the mitochondrial membrane directly?

Accepted Answer

It is converted to malate in the cytosol, which can cross the membrane, and then re-oxidized to oxaloacetate in the mitochondria.

Question 16

Which of the following best describes the fate of citrate when it is shuttled out of the mitochondria into the cytosol?

Accepted Answer

It is cleaved by citrate lyase to generate acetyl-CoA and oxaloacetate for fatty acid synthesis.

Question 17

Which of the following is a regulatory effect of a high insulin/glucagon ratio on glycolysis in the liver?

Accepted Answer

Dephosphorylation and activation of phosphofructokinase-2 (PFK-2), increasing fructose-2,6-bisphosphate levels.

Question 18

A patient with a deficiency in the enzyme aconitase would have impaired conversion of which TCA cycle intermediate?

Accepted Answer

Citrate to isocitrate

Question 19

Which of the following best describes the role of NAD$$^+ in $$glycolysis and the TCA cycle?

Accepted Answer

It acts as an electron acceptor, becoming reduced to NADH during oxidation reactions.

Question 20

Which of the following reactions is an example of a substrate-level phosphorylation in the TCA cycle?

Accepted Answer

Conversion of succinyl-CoA to succinate by succinate thiokinase

Glycolysis and the TCA Cycle: Regulation, Pathways, and Connections

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