In Kreb's cycle -

Options

A. Acetyl coenzyme A undergoes 4 oxidations and 2 decarboxylations
B. Pyruvic acid undergoes 4 oxidations and 2 decarboxylations
C. TCA undergoes 4 oxidations nd 4 decarboxylations
D. OAA undergoes 4 oxidation and 2 decarboxylations.

Answer

### Step-by-Step Solution for the Question on Kreb's Cycle:

1. **Understanding the Kreb's Cycle**: The Kreb's cycle, also known as the citric acid cycle or TCA cycle, is a crucial metabolic pathway that takes place in the mitochondria of cells. It is responsible for the oxidation of acetyl-CoA to produce energy.

2. **Entry of Acetyl-CoA**: The cycle begins when acetyl-CoA, a 2-carbon molecule, combines with oxaloacetic acid (OAA), a 4-carbon compound, to form citric acid (6-carbon compound). This is the first step of the cycle.

3. **Decarboxylation and Oxidation**: Throughout the cycle, there are two key processes: decarboxylation (removal of carbon dioxide) and oxidation (loss of electrons). In the Kreb's cycle:
- Two molecules of CO2 are released during the conversion of citric acid to alpha-ketoglutarate (5-carbon) and then to succinyl-CoA (4-carbon).
- The cycle also involves four oxidation reactions where NAD+ and FAD are reduced to NADH and FADH2, respectively.

4. **Formation of Intermediate Compounds**: The cycle progresses through several intermediate compounds:
- Citric acid (6C) → Alpha-ketoglutarate (5C) → Succinyl-CoA (4C) → Succinate (4C) → Fumarate (4C) → Malate (4C) → Oxaloacetic acid (4C).

5. **Regeneration of Oxaloacetic Acid**: The cycle ends with the regeneration of oxaloacetic acid, which is necessary for the cycle to continue. This regeneration occurs after the last oxidation of malate to oxaloacetic acid.

6. **Summary of Key Points**:
- The Kreb's cycle involves 4 oxidation reactions and 2 decarboxylation reactions.
- The correct option for the Kreb's cycle based on the processes involved is the one that states "Acetyl-CoA undergoes 4 oxidations and 2 decarboxylations".

### Final Answer:
The correct option is that Acetyl-CoA undergoes 4 oxidations and 2 decarboxylations in the Kreb's cycle.

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