Q: Which of the following equations correctly represents the overall oxidative phase of the pentose phosphate pathway for one molecule of glucose 6-phosphate?

$$\mathrm{Glucose\ 6\text{-}phosphate} + 2\ NADP^+ + H_2O \rightarrow \mathrm{Ribulose\ 5\text{-}phosphate} + 2\ NADPH + CO_2 + 2\ H^+$$

Question 1

Which of the following best describes the main function of the pentose phosphate pathway (PPP) in red blood cells?

Accepted Answer

To provide NADPH for the reduction of glutathione and detoxification of reactive oxygen species

Question 2

Which enzyme catalyzes the rate-limiting step of the pentose phosphate pathway, and what is its main regulatory mechanism?

Accepted Answer

Glucose 6-phosphate dehydrogenase (G6PD); inhibited by high NADPH/NADP$^+$ ratio

Question 3

A patient with G6PD deficiency is given an oxidant drug and develops hemolytic anemia. Which of the following best explains the underlying biochemical defect?

Accepted Answer

Impaired regeneration of reduced glutathione (G-SH) due to insufficient NADPH

Question 4

Which of the following reactions in the pentose phosphate pathway is irreversible?

Accepted Answer

Oxidation of glucose 6-phosphate to 6-phosphoglucono-δ-lactone by G6PD

Question 5

Which of the following best describes the fate of carbon 1 of glucose 6-phosphate during the oxidative phase of the PPP?

Accepted Answer

It is released as carbon dioxide ($CO_2$)

Question 6

A researcher is studying the nonoxidative phase of the PPP. Which of the following enzymes is responsible for transferring a two-carbon unit between sugar phosphates?

Accepted Answer

Transketolase

Question 7

Which of the following tissues is expected to have the highest activity of the pentose phosphate pathway and why?

Accepted Answer

Liver, due to active fatty acid and cholesterol biosynthesis requiring NADPH

Question 8

Which of the following best explains why G6PD deficiency confers resistance to Plasmodium falciparum malaria?

Accepted Answer

Reduced ability of the parasite to survive oxidative stress in G6PD-deficient red blood cells

Question 9

Which of the following is a direct product of the oxidative phase of the pentose phosphate pathway?

Accepted Answer

Ribulose 5-phosphate

Question 10

A mutation in the gene encoding transaldolase would most directly impair which of the following processes?

Accepted Answer

Interconversion of sugar phosphates in the nonoxidative phase of the PPP

Question 11

Which of the following best describes the role of NADPH in the cytochrome P450 monooxygenase system?

Accepted Answer

It donates electrons required for the hydroxylation of substrates

Question 12

Which of the following equations correctly represents the overall oxidative phase of the pentose phosphate pathway for one molecule of glucose 6-phosphate?

Accepted Answer

$$\mathrm{Glucose\ 6	ext{-}phosphate} + 2\ NADP^+ + H_2O ightarrow \mathrm{Ribulose\ 5	ext{-}phosphate} + 2\ NADPH + CO_2 + 2\ H^+$$

Question 13

Which of the following statements about the nonoxidative phase of the PPP is correct?

Accepted Answer

It allows the interconversion of sugars with three to seven carbons, linking the PPP to glycolysis

Question 14

A patient with chronic granulomatous disease has a defect in which enzyme, and what is the clinical consequence?

Accepted Answer

NADPH oxidase; recurrent infections due to impaired phagocytic killing

Question 15

Which of the following best explains why red blood cells are particularly vulnerable to oxidative damage in G6PD deficiency?

Accepted Answer

They lack mitochondria and rely solely on the PPP for NADPH production

Question 16

Which of the following is a function of nitric oxide (NO) produced by endothelial nitric oxide synthase (eNOS)?

Accepted Answer

Activates guanylyl cyclase, increasing cGMP and causing vasodilation

Question 17

Which of the following best describes the role of glutathione peroxidase in red blood cells?

Accepted Answer

It reduces hydrogen peroxide to water using reduced glutathione (G-SH)

Question 18

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

Accepted Answer

It supplies ribose 5-phosphate for nucleotide and nucleic acid synthesis

Question 19

A patient is found to have a mutation that decreases the binding affinity of G6PD for glucose 6-phosphate. Which of the following is the most likely clinical consequence?

Accepted Answer

Chronic hemolytic anemia, especially under oxidative stress

Pentose Phosphate Pathway and NADPH: Biochemical Roles and Clinical Relevance

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