Choose the correct statement/s about amphibolic pathways.

Options

A. Fatty acids are used as a substrate when they are converted into acetyle CoA to enter the respiratory pathways.
B. A pathway is said to be amphibolic when it can only perform catabolic activities like the breakdown of proteins into amino acids.
C. Glycerol enters the Kreb's cycle as PGAL.
D. Both (A) and (B)

Answer

To solve the question about amphibolic pathways, let's break down the information step by step.

### Step-by-Step Solution:

1. **Understanding Amphibolic Pathways**:
- Amphibolic pathways are metabolic pathways that involve both catabolism (the breakdown of molecules) and anabolism (the synthesis of molecules). This means they can function in both energy-releasing and energy-consuming processes.

**Hint**: Remember that "amphibolic" refers to pathways that can do both breakdown and synthesis.

2. **Evaluating the Statements**:
- We have to evaluate the given statements about amphibolic pathways to identify which one is correct.

3. **Analyzing the First Statement**:
- The first statement mentions that fatty acids are used as a substrate when they are converted into acetyl coenzyme A to enter the respiratory pathway. This is true because fatty acids undergo beta-oxidation to form acetyl CoA, which then enters the Krebs cycle for energy production.

**Hint**: Think about how fatty acids are metabolized in the body and their role in energy production.

4. **Analyzing the Second Statement**:
- The second statement claims that a pathway is called amphibolic only if it can perform catabolic activities. This is incorrect because amphibolic pathways must involve both catabolic and anabolic processes.

**Hint**: Recall that amphibolic pathways are defined by their dual role, not just catabolism.

5. **Analyzing the Third Statement**:
- The third statement suggests that glycerol enters the Krebs cycle as phosphoglyceraldehyde (PGAL). This is incorrect because glycerol is converted into dihydroxyacetone phosphate (DHAP) and then into glyceraldehyde-3-phosphate (G3P), which is an intermediate in glycolysis, not directly into the Krebs cycle.

**Hint**: Consider the metabolic pathways of glycerol and how it is processed before entering the Krebs cycle.

6. **Conclusion**:
- Based on the analysis, the only correct statement is the first one about fatty acids being converted into acetyl CoA.

### Final Answer:
The correct statement about amphibolic pathways is: **Fatty acids are used as a substrate when they are converted into acetyl coenzyme A to enter the respiratory pathway.**