Question

Which pathway reduces the most NAD+?

1. Glycolysis

2. Pyruvate Dehydrogenase Complex

3. Both Pyruvate Dehydrogenase Complex & Glycolysis are the same as each other but greater than fermentation

4. Fermentation

Answer 1

Option 1.

One molecule of glucose in glycolysis produces 2 molecules of pyruvate and reduces two NAD+.

Glucose + 2 NAD+ + 2 ADP + 2 Pi à 2 Pyruvate + 2 NADH + 2 H+ + 2 ATP + 2 H2O

Option 2.

Two molecules of pyruvate formed by glycolysis produces two molecules of acetyl Co-A and reduces NAD+.

Pyruvate + CoASH + NAD+ → Acetyl-CoA + CO2 + NADH + H+

Pyruvate dehydrogenase complex reduces two NAD+ for one glucose molecules broken down in glycolysis.

Option 3.

Two NAD+ are reduced in both glycolysis and pyruvate dehydrogenase complex which are greater than fermentation.

Option 4.

Fermentation includes vigorous oxidation of NADH to NAD+.

When oxygen is limited, the oxidation of NADH to NAD+ by the electron transport chain is insufficient to maintain glycolysis, so NAD+ is regenerated by the reduction of pyruvate to lactate.

Pyruvate + NADH --> Ethanol + NAD+

Here, NADH is oxidised to NAD+

OPTION 3 IS THE MOST APPROPRIATE.