Question 1

Which of the following best explains why phosphorylation of glucose favors its retention inside the cell?

Accepted Answer

Phosphorylation increases the negative charge, preventing glucose from crossing the plasma membrane.

Question 2

Which statement about the fate of carbons from acetyl-CoA in human metabolism is correct?

Accepted Answer

Acetyl-CoA carbons are fully oxidized to CO₂ in the TCA cycle and do not provide net carbon for glucose synthesis.

Question 3

A patient with a deficiency in glucose-6-phosphatase would most likely experience which metabolic consequence?

Accepted Answer

Impaired ability to release free glucose from the liver during fasting.

Question 4

Which equation correctly relates the actual free energy change ($$\Delta G) of a $$reaction to its standard free energy change ($$\Delta G^\circ{}') $$and the reaction quotient ($$Q$$)?

Accepted Answer

$$\Delta G = \Delta G^\circ{}' + RT \ln Q$$

Question 5

Why does blocking lactate dehydrogenase (LDH) slow glycolysis in mature red blood cells?

Accepted Answer

LDH is required to regenerate NAD⁺, which is essential for glycolysis to continue.

Question 6

Which of the following best describes the role of NADPH produced by the pentose phosphate pathway (PPP)?

Accepted Answer

NADPH provides reducing power for biosynthesis and antioxidant defense.

Question 7

Which glycolytic enzyme catalyzes the committed step of glycolysis, and what is the main allosteric activator of this enzyme?

Accepted Answer

Phosphofructokinase-1 (PFK-1); activated by AMP and fructose-2,6-bisphosphate (F2,6BP)

Question 8

During fasting, which hormonal and enzymatic changes occur in the liver to favor gluconeogenesis over glycolysis?

Accepted Answer

Glucagon increases, leading to phosphorylation of PFK-2/FBPase-2, decreasing F2,6BP and favoring gluconeogenesis.

Question 9

Which of the following is a correct summary of the energy investment and payoff phases of glycolysis per molecule of glucose?

Accepted Answer

Investment: 2 ATP consumed; Payoff: 4 ATP and 2 NADH produced.

Question 10

A mutation causes muscle glycogen phosphorylase to be inactive. Which is the most likely physiological consequence during intense exercise?

Accepted Answer

Muscle cannot rapidly mobilize glucose from glycogen, leading to early fatigue.

Question 11

Which of the following reactions is coupled with ATP hydrolysis to drive it forward, and what is the net standard free energy change ($$\Delta G^\circ{}') $$for the coupled reaction?

Accepted Answer

Glucose + ATP \rightarrow G6P + ADP; $$\Delta G^\circ{}' = -16.7 kJ/$$mol

Question 12

Which of the following best explains why the pentose phosphate pathway (PPP) is important for rapidly dividing cells?

Accepted Answer

PPP provides ribose-5-phosphate for nucleotide synthesis and NADPH for biosynthetic reactions.

Question 13

Which of the following statements about the regulation of glycolysis and gluconeogenesis in the liver is correct?

Accepted Answer

Fructose-2,6-bisphosphate (F2,6BP) activates glycolysis and inhibits gluconeogenesis.

Question 14

A patient is given a drug that inhibits the pentose phosphate pathway. Which cellular process would be most directly affected?

Accepted Answer

Reductive biosynthesis and antioxidant defense due to decreased NADPH.

Question 15

Which of the following is true regarding the reversible conversion of pyruvate to lactate?

Accepted Answer

It is coupled to the interconversion of NADH and NAD⁺, helping regenerate NAD⁺ for glycolysis.

Question 16

Which of the following best describes the main difference in glycogen metabolism between liver and skeletal muscle?

Accepted Answer

Liver glycogen supports blood glucose; muscle glycogen supports local contraction.

Question 17

Which of the following is a correct bypass reaction in gluconeogenesis for the irreversible glycolytic step catalyzed by pyruvate kinase?

Accepted Answer

Pyruvate carboxylase and PEP carboxykinase convert pyruvate to phosphoenolpyruvate.

Question 18

If the actual free energy change ($$\Delta G) $$for a reaction is positive in the cell, which of the following is true?

Accepted Answer

The reverse reaction is favored under cellular conditions.

Question 19

Which of the following best explains why glycolysis must regenerate NAD⁺?

Accepted Answer

NAD⁺ is required as an electron acceptor for the oxidation of glyceraldehyde-3-phosphate.

Metabolism: Carbon Flow, Energy, and Regulation in Biochemistry

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