Question

During lactic acid fermentation, pyruvic acid is reduced to lactic acid using one proton and two electrons from ________________.

• A. \(\text{NADH}+\text{H}^{+}\) produced during glycolysis.
• B. \(\text{FADH}_{2}\) produced in Krebs cycle.
• C. Acetyl CoA.
• D. Water.

Hint:

Pyruvic acid is reduced by NADH + H+ formed in glycolysis.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
In glycolysis, oxidation of glyceraldehyde-3-phosphate reduces \(\text{NAD}^{+}\) to \(\text{NADH} + \text{H}^{+}\).

Step 2: Lactic acid fermentation
Lactate dehydrogenase uses this \(\text{NADH} + \text{H}^{+}\) to reduce pyruvate:
\(\text{pyruvic acid} + \text{NADH} + \text{H}^{+} \rightarrow \text{lactic acid} + \text{NAD}^{+}\)

Step 3: Why it matters
This regenerates \(\text{NAD}^{+}\) so that glycolysis can continue without oxygen. The Krebs cycle is not involved.

Final Answer:
The proton and electrons come from NADH + H+ produced during glycolysis. \[ \boxed{\text{(A) }\text{NADH}+\text{H}^{+}\text{ produced during glycolysis.}} \]