The rate of breakdown of glucose into pyruvic acid is under certain controlling steps. The major controlling step is :-

Options

A. Fructose 6–P `to` Fructose 1, 6 bisphosphate
B. PGAL `to` 1, 3 bisphosphoglyceric acid
C. Glucose 6-P `to` Fructose 6-P
D. 3PGA `to` 2PGA

Answer

To determine the major controlling step in the breakdown of glucose into pyruvic acid, we need to analyze the glycolysis pathway, which consists of several key steps. Here's a step-by-step breakdown of the process:

### Step 1: Understanding Glycolysis
Glycolysis is the metabolic pathway that converts glucose into pyruvic acid. It consists of a series of enzymatic reactions that occur in the cytoplasm of the cell. The overall reaction of glycolysis can be summarized as:
\[ \text{Glucose} \rightarrow \text{2 Pyruvate} + \text{ATP} + \text{NADH} \]

### Step 2: Identifying Key Steps in Glycolysis
Glycolysis includes several important steps, among which the following are significant:
1. **Phosphorylation of Glucose**: Glucose is phosphorylated to form glucose-6-phosphate.
2. **Isomerization**: Glucose-6-phosphate is converted into fructose-6-phosphate.
3. **Phosphorylation of Fructose-6-Phosphate**: This step converts fructose-6-phosphate into fructose-1,6-bisphosphate.
4. **Cleavage**: Fructose-1,6-bisphosphate is split into two 3-carbon fragments.

### Step 3: Identifying the Major Controlling Step
Among these steps, the conversion of **fructose-6-phosphate to fructose-1,6-bisphosphate** is considered the major controlling step. This step is catalyzed by the enzyme phosphofructokinase (PFK), which is a key regulatory enzyme in glycolysis. The activity of PFK is influenced by various factors, including the levels of ATP and AMP, making it a crucial control point in the pathway.

### Conclusion
Thus, the major controlling step in the breakdown of glucose into pyruvic acid is:
**Fructose-6-phosphate to fructose-1,6-bisphosphate.**

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