Which one of the following catabolism stages produces NADH?

• A. Electron transport chain
• B. Glycogenolysis
• C. Digestion
• D. Citric acid cycle

Answer: (D)

Verified step by step guidance

1. Understand the role of NADH in cellular metabolism: NADH is a key electron carrier in cellular respiration, transferring electrons to the electron transport chain.
2. Identify the stages of catabolism: Catabolism involves breaking down molecules to release energy, and it includes stages like digestion, glycolysis, the citric acid cycle, and the electron transport chain.
3. Review the citric acid cycle: Also known as the Krebs cycle, this stage occurs in the mitochondria and is crucial for oxidizing acetyl-CoA to CO2, while reducing NAD+ to NADH.
4. Compare the stages: Digestion breaks down food into smaller molecules, glycogenolysis converts glycogen to glucose, and the electron transport chain uses NADH to produce ATP, but does not produce NADH itself.
5. Conclude that the citric acid cycle is the stage where NADH is produced, as it involves multiple steps where NAD+ is reduced to NADH during the oxidation of acetyl-CoA.