Q: Which glycolytic intermediate has the highest phosphate-group transfer potential, and what is the standard free-energy change for its hydrolysis?

Phosphoenolpyruvate; $$\Delta G$$^{\circ'}$$ = -61.9\ \text{kJ mol}^{-1}$$

Q: Which enzyme catalyzes the first ATP-producing reaction in glycolysis, and what is the reaction equation?

Phosphoglycerate kinase; $$1,3\text{-Bisphosphoglycerate} + \text{ADP} \rightarrow 3\text{-Phosphoglycerate} + \text{ATP}$$

Question 1

Which reaction in glycolysis is the only oxidation–reduction reaction, and what is the overall equation for this step?

Accepted Answer

Conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate; $$	ext{Glyceraldehyde-3-phosphate} + 	ext{NAD}^+ + P_i ightarrow 1,3	ext{-bisphosphoglycerate} + 	ext{NADH} + H^+$$

Question 2

During the oxidation of glyceraldehyde-3-phosphate in glycolysis, which molecule acts as the electron acceptor?

Accepted Answer

NAD$$^+$$

Question 3

Which glycolytic intermediate has the highest phosphate-group transfer potential, and what is the standard free-energy change for its hydrolysis?

Accepted Answer

Phosphoenolpyruvate; $$\Delta G$$^{\circ'}$$ = -61.9\ 	ext{kJ mol}^{-1}$$

Question 4

Which enzyme catalyzes the first ATP-producing reaction in glycolysis, and what is the reaction equation?

Accepted Answer

Phosphoglycerate kinase; $$1,3	ext{-Bisphosphoglycerate} + 	ext{ADP} ightarrow 3	ext{-Phosphoglycerate} + 	ext{ATP}$$

Question 5

Which three enzymes represent the major control points of glycolysis?

Accepted Answer

Hexokinase, phosphofructokinase, and pyruvate kinase

Question 6

A toxin inhibits glyceraldehyde-3-phosphate dehydrogenase. What is the most immediate effect on glycolysis?

Accepted Answer

Decreased NADH production, decreased ATP production, and decreased pyruvate formation

Question 7

Which of the following best describes substrate-level phosphorylation in glycolysis?

Accepted Answer

Direct transfer of a phosphate group from a high-energy substrate to ADP, forming ATP

Question 8

Which two glycolytic reactions involve substrate-level phosphorylation?

Accepted Answer

Reactions 7 and 10

Question 9

Why is the rearrangement of 3-phosphoglycerate to 2-phosphoglycerate necessary in glycolysis?

Accepted Answer

To prepare the molecule for dehydration and formation of a high-energy intermediate

Question 10

What is the net ATP gain per molecule of glucose during glycolysis?

Accepted Answer

$$2$$

Question 11

Which of the following best explains why phosphoenolpyruvate (PEP) can drive ATP synthesis?

Accepted Answer

PEP hydrolysis releases more free energy than ATP hydrolysis, making phosphate transfer highly exergonic

Question 12

Which of the following is NOT a feature of the three major control points in glycolysis?

Accepted Answer

They are reversible under cellular conditions

Question 13

If a muscle cell has a very high ATP concentration, what is the expected effect on glycolysis?

Accepted Answer

Phosphofructokinase and pyruvate kinase activities decrease, slowing glycolysis

Question 14

Which statement best describes the fate of NADH produced during glycolysis under anaerobic conditions?

Accepted Answer

NADH is used to reduce pyruvate to lactate, regenerating NAD$$^+$$

Question 15

Which enzyme catalyzes the final step of glycolysis, and what are the required cofactors?

Accepted Answer

Pyruvate kinase; Mg$$^{2+}$$ and K$$^+$$

Question 16

A mutation causes pyruvate kinase to become inactive. What is the most likely effect on phosphoenolpyruvate (PEP) concentration?

Accepted Answer

PEP concentration increases

Question 17

Which of the following best describes the role of the essential cysteine residue in glyceraldehyde-3-phosphate dehydrogenase?

Accepted Answer

It forms a covalent thioester intermediate with the substrate, conserving oxidation energy

Question 18

Which of the following is a correct summary of the products formed during the payoff phase of glycolysis per molecule of glucose?

Accepted Answer

2 NADH, 4 ATP, 2 pyruvate

Question 19

Which of the following best explains why the standard free-energy change ($$\Delta G$$^{\circ'}$$) for a reaction may differ from the actual cellular free-energy change ($$\Delta G$$)?

Accepted Answer

Cellular free-energy change depends on actual substrate and product concentrations, temperature, and physiological state

The Payoff Phase of Glycolysis: Reactions, Energetics, and Regulation

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