Which metabolic process is common to both aerobic cellular respiration and alcoholic fermentation?

Question

BlackTom AI · Accepted Answer

Glycolysis occurs in the cytosol and converts one glucose into two molecules of pyruvate, producing a net yield of 2 ATP and 2 NADH; this pathway operates in both aerobic cellular respiration and alcoholic fermentation.

Relevant knowledge points:
- Glycolysis is an anaerobic cytosolic pathway that does not require oxygen and is the first step in both respiration and fermentation.
- Aerobic respiration continues after glycolysis with pyruvate oxidation (to acetyl-CoA), the Krebs (citric acid) cycle, and the electron transport chain (ETC) with a proton gradient for oxidative phosphorylation.
- Alcoholic fermentation uses glycolysis followed by reactions that convert pyruvate to ethanol, regenerating NAD+ so glycolysis can continue.

Step-by-step reasoning:
1. Glycolysis: Glucose + 2 NAD+ + 2 ADP + 2 Pi → 2 Pyruvate + 2 NADH + 2 ATP + 2 H2O + 2 H+. This net stoichiometry (2 ATP, 2 NADH, 2 pyruvate) holds in both processes and occurs in the cytosol.
2. In aerobic respiration, pyruvate is transported into mitochondria and converted to acetyl-CoA, then enters the Krebs cycle; electrons from NADH/FADH2 go to the ETC to build a proton gradient and drive ATP synthesis.
3. In alcoholic fermentation (e.g., yeast), pyruvate is decarboxylated to acetaldehyde then reduced to ethanol, oxidizing NADH back to NAD+ so glycolysis can continue; no ETC or significant proton gradient is produced.

Why the correct answer is correct:
Glycolysis is the sole metabolic step common to both routes because it precedes the divergent fates of pyruvate and does not require oxygen.

Why other options are incorrect:
- Electron transport chain: requires mitochondrial membranes and oxygen as final acceptor—absent in fermentation.
- Krebs cycle: occurs in mitochondrial matrix and is part of aerobic respiration only.
- Conversion of pyruvic acid to acetyl CoA: is an oxidative mitochondrial step not used in alcoholic fermentation.
- Production of a proton gradient: characteristic of oxidative phosphorylation (aerobic); fermentation does not generate this for ATP synthesis.

Conclusion: The correct answer is Glycolysis, matching the provided answer.

Which metabolic process is common to both aerobic cellular respiration and alcoholic fermentation?单项选择题

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