Question 1

Which of the following best describes the overall reaction of glycolysis, including the net energy yield and the fate of major reactants and products?

$$\mathrm{Glucose} + 2\mathrm{NAD}^+ + 2\mathrm{ADP} + 2\mathrm{P_i} \rightarrow 2\mathrm{Pyruvate} + 2\mathrm{NADH} + 2\mathrm{ATP} + 2\mathrm{H_2O} + 4\mathrm{H}^+$$

What is the standard free energy change ($$\Delta G^\circ') $$for this process?

Accepted Answer

$$\Delta G^\circ' = -22\ \mathrm{kcal/mol}$$

Question 2

Refer to the energy diagram of glycolysis (stepwise staircase). Which step is considered the committed, rate-limiting step of glycolysis, and what enzyme catalyzes this reaction?

Accepted Answer

Step 3, catalyzed by phosphofructokinase (PFK)

Question 3

Which of the following best explains why hexokinase is not the primary regulatory point of glycolysis, despite catalyzing the first step?

Accepted Answer

Hexokinase is almost always active due to its low Km, and its product (glucose-6-phosphate) can enter other metabolic pathways.

Question 4

A yeast mutant has a phosphofructokinase (PFK) that cannot bind fructose-2,6-bisphosphate (F26BP). What is the most likely consequence for glycolysis in this mutant?

Accepted Answer

Glycolysis rate decreases due to loss of allosteric activation.

Question 5

In red blood cells, vanadate inhibits GAPDH by interacting with essential —SH groups. What happens to the cellular levels of ATP, inorganic phosphate ($$P_i$$), and 2,3-bisphosphoglycerate (2,3-BPG) when cells are incubated with vanadate?

Accepted Answer

ATP and 2,3-BPG decrease; $$P_i$$ increases.

Question 6

Which of the following statements about the regulation of phosphofructokinase (PFK) is correct?

Accepted Answer

PFK is inhibited by phosphoenolpyruvate (PEP) and activated by fructose-2,6-bisphosphate.

Question 7

Which enzyme is responsible for phosphorylating glucose to glucose-6-phosphate in the first step of glycolysis, and what is the significance of this reaction?

Accepted Answer

Hexokinase or glucokinase; it traps glucose inside the cell.

Question 8

In the absence of oxygen, what is the fate of pyruvate and NADH produced during glycolysis in muscle cells?

Accepted Answer

Pyruvate is converted to lactate by lactate dehydrogenase, regenerating NAD+.

Question 9

Which of the following best describes the difference in glucose affinity between hexokinase and glucokinase, as shown in the enzyme activity graph?

Accepted Answer

Hexokinase has a lower Km and higher affinity for glucose than glucokinase.

Question 10

Which of the following is a possible fate of pyruvate in human metabolism under aerobic conditions?

Accepted Answer

Entry into the citric acid cycle as acetyl-CoA.

Question 11

Which glycolytic intermediate is a precursor for 2,3-bisphosphoglycerate (2,3-BPG) synthesis in red blood cells?

Accepted Answer

1,3-bisphosphoglycerate

Question 12

Which of the following best explains why phosphofructokinase (PFK) activity increases when cellular energy status is low?

Accepted Answer

High ADP levels promote F-6-P binding to PFK.

Question 13

A patient with a deficiency in lactate dehydrogenase (LDH) would most likely experience which of the following during intense exercise?

Accepted Answer

Decreased ability to regenerate NAD+, leading to impaired glycolysis.

Question 14

Which of the following statements about the energy investment and payoff phases of glycolysis is correct?

Accepted Answer

The investment phase consumes ATP, while the payoff phase produces ATP and NADH.

Question 15

Which of the following is a direct consequence of inhibiting GAPDH in glycolysis?

Accepted Answer

Accumulation of glyceraldehyde-3-phosphate and decreased ATP production.

Question 16

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

Accepted Answer

NAD+ is reduced to NADH during the oxidation of glyceraldehyde-3-phosphate.

Glycolysis: Pathways, Regulation, and Energy Yield

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