Which of the metabolites is common to respiration mediated breakdown of fats, carbohydrates and proteins ?

Options

A. Pyruvic acid
B. Acetyl CoA
C. Glucose - 6 -phosphate
D. Fructose 1, 6 -bisphosphate

Answer

To determine the common metabolite involved in the respiration-mediated breakdown of fats, carbohydrates, and proteins, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Carbohydrate Breakdown**:
- Carbohydrates, primarily in the form of glucose, undergo glycolysis.
- During glycolysis, glucose (a six-carbon compound) is broken down into two molecules of pyruvic acid (a three-carbon compound).

2. **Conversion of Pyruvic Acid**:
- Pyruvic acid then enters the mitochondria and is converted into acetyl coenzyme A (acetyl CoA) by combining with coenzyme A.
- This conversion releases one molecule of carbon dioxide and results in the formation of a two-carbon compound, acetyl CoA.

3. **Understanding Fat Breakdown**:
- Fats are broken down into fatty acids through a process called lipolysis.
- These fatty acids then enter the mitochondria and undergo beta-oxidation, where they are converted into acetyl CoA.

4. **Understanding Protein Breakdown**:
- Proteins are broken down into amino acids through the process of proteolysis.
- These amino acids can be converted into various intermediates, but many of them can also be transformed into acetyl CoA, depending on their structure.

5. **Common Metabolite**:
- After analyzing the breakdown pathways of carbohydrates (glucose to pyruvic acid to acetyl CoA), fats (fatty acids to acetyl CoA), and proteins (amino acids to acetyl CoA), we find that the common metabolite that enters the Krebs cycle (aerobic respiration) is **acetyl coenzyme A**.

### Final Answer:
The common metabolite to the respiration-mediated breakdown of fats, carbohydrates, and proteins is **acetyl coenzyme A**.

---