The Role of the Oxidative Phase of PPP in NADPH Generation for Fatty Acid Synthesis in Liver Cells

The pentose phosphate pathway (PPP) plays an important role in balancing metabolic pathways to ensure the body’s needs are met under different growth conditions. What happens in liver cells that are synthesizing fatty acids? (These cells need more NADPH than ribose 5-phosphate.)a. Glycolysis predominates and nonoxidative PPP is used to make ribose 5- phosphateb. Only the oxidative phase of PPP is activec. The oxidative and nonoxidative phases of PPP are used. The fructose 6-phosphate (F6P) and glyceraldehyde 3-phosphate (G3P) produced in thenonoxidative phase going through glycolysis.d. The oxidative and nonoxidative phases of PPP are used. The F6P and G3P produced by the nonoxidative phase are converted to glucose 6-phosphatee. The oxidative phase of PPP is run in reverse to balance cellular the cellular ratio of NADPH/NADP+

d. The oxidative and nonoxidative phases of PPP are used. The F6P and G3P produced by the nonoxidative phase are converted to glucose 6-phosphate

The correct answer is b. Only the oxidative phase of PPP is active.

Liver cells synthesizing fatty acids require a high amount of NADPH for the reductive biosynthesis of fatty acids from acetyl-CoA. The oxidative phase of the PPP generates NADPH and is therefore preferred over the nonoxidative phase, which produces ribose-5-phosphate for nucleotide synthesis. In the oxidative phase of PPP, glucose-6-phosphate is converted to ribulose-5-phosphate via a series of reactions that generate NADPH as a byproduct. Thus, liver cells synthesize fatty acids by relying predominantly on glycolysis for energy production and the oxidative phase of PPP for NADPH generation. The other options (a, c, d, and e) do not reflect the metabolic requirements of liver cells synthesizing fatty acids and are therefore incorrect.

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