When a molecule of pyruvic acid is subjected to anaerobic oxidation and forms lactic acid, there is

Options

A. Loss of 3 ATP molecules
B. Loss of 6 ATP molecules
C. Gain of 2 ATP molecules
D. Gain of 4 ATP molecules

Answer

To solve the question regarding the anaerobic oxidation of pyruvic acid to lactic acid, we can break down the process step by step:

### Step-by-Step Solution:

1. **Understanding Pyruvic Acid**: Pyruvic acid is a key intermediate in several metabolic pathways. It is produced during glycolysis, which is the breakdown of glucose.

2. **Anaerobic Conditions**: Under anaerobic conditions (absence of oxygen), pyruvic acid cannot enter the Krebs cycle. Instead, it undergoes fermentation.

3. **Lactic Acid Fermentation**: In lactic acid fermentation, pyruvic acid is converted into lactic acid. This process involves the reduction of pyruvic acid, where NADH (produced during glycolysis) donates electrons to pyruvic acid.

4. **NADH and NAD+**: During this conversion, NADH is oxidized back to NAD+. This is crucial because it allows glycolysis to continue by regenerating NAD+, which is necessary for the production of ATP in glycolysis.

5. **ATP Production**: In the process of glycolysis, a net gain of 2 ATP molecules is produced from one molecule of glucose, which is converted to two molecules of pyruvic acid. However, during the conversion of pyruvic acid to lactic acid, there is no additional ATP produced.

6. **Net ATP Loss**: Since the conversion of pyruvic acid to lactic acid does not produce any additional ATP and only regenerates NAD+, we can conclude that there is a loss of 3 ATP molecules when considering the overall energy yield from glucose metabolism. This is because the energy that could have been produced in aerobic respiration (which yields more ATP) is not realized in anaerobic conditions.

7. **Final Answer**: Therefore, when a molecule of pyruvic acid is subjected to anaerobic oxidation and forms lactic acid, there is a loss of 3 ATP molecules.

### Conclusion:
The correct answer to the question is: **Loss of 3 ATP molecules**.