Correct option is D
Fermentation allows glycolysis to continue in the absence of oxygen by regenerating NAD⁺ from NADH. During glycolysis, glucose is broken down into pyruvate, producing ATP and NADH. However, without oxygen, NADH cannot be used in the electron transport chain for ATP production. Instead, yeast cells convert pyruvate into ethanol and carbon dioxide, regenerating NAD⁺ in the process. This ensures that glycolysis can continue, allowing the cell to keep producing ATP anaerobically.
Information Booster:
- Alcohol fermentation is an anaerobic process carried out by yeast and some bacteria.
- Key steps: Glucose → Pyruvate → Acetaldehyde → Ethanol.
- NAD⁺ regeneration is crucial for keeping glycolysis active in the absence of oxygen.
- Fermentation does not generate additional ATP beyond glycolysis but ensures that ATP production continues.
- The enzyme alcohol dehydrogenase catalyzes the conversion of acetaldehyde to ethanol, regenerating NAD⁺.
- Fermentation is used in bread-making, brewing, and biofuel production.
Additional Knowledge:
(a) Converting acetaldehyde to alcohol to prevent feedback inhibition:
- While acetaldehyde is converted to ethanol, this is not primarily for preventing feedback inhibition.
- The main goal is to regenerate NAD⁺ for glycolysis.
(b) Generating NADH for mitochondrial ATP generation:
- Fermentation occurs in the absence of oxygen, so NADH cannot be used for mitochondrial ATP synthesis.
- Instead, fermentation converts NADH back to NAD⁺.
(c) Preventing toxicity of acetaldehyde:
- Acetaldehyde is toxic in high amounts, but its conversion to ethanol is mainly for NAD⁺ regeneration, not just detoxification.
(d) Generating NAD⁺ for glycolysis (Correct Answer):
- Glycolysis requires NAD⁺ as an electron acceptor.
- Without oxygen, NADH accumulates, stopping glycolysis.
- Fermentation converts NADH back to NAD⁺, allowing glycolysis to continue.
