During cellular respiration, number of ATP used during conversion of glucose into glyceraldehyde-3-phosphate is

Options

A. 1
B. 2
C. 3
D. 4

Answer

To determine the number of ATP molecules used during the conversion of glucose into glyceraldehyde-3-phosphate in cellular respiration, we can follow these steps:

### Step-by-Step Solution

1. **Understanding Glycolysis**: Glycolysis is the first step in the breakdown of glucose, which occurs in the cytoplasm of the cell. It converts one molecule of glucose (a six-carbon compound) into two molecules of pyruvic acid (a three-carbon compound).

2. **Initial Conversion**: The first step in glycolysis involves the conversion of glucose into glucose-6-phosphate. This reaction is catalyzed by the enzyme hexokinase, and it requires one ATP molecule. During this process, ATP is converted into ADP and inorganic phosphate.

3. **Isomerization**: The glucose-6-phosphate is then converted into fructose-6-phosphate through an isomerization reaction, which does not require ATP.

4. **Phosphorylation**: The fructose-6-phosphate is then converted into fructose-1,6-bisphosphate. This step is catalyzed by the enzyme phosphofructokinase and requires another ATP molecule. Again, ATP is converted into ADP and inorganic phosphate.

5. **Splitting of Fructose-1,6-bisphosphate**: The fructose-1,6-bisphosphate is then split into two three-carbon molecules: dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. This step does not require any additional ATP.

6. **Total ATP Used**: In total, two ATP molecules are used during the conversion of glucose to glyceraldehyde-3-phosphate (one for the conversion of glucose to glucose-6-phosphate and another for the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate).

### Final Answer
The number of ATP used during the conversion of glucose into glyceraldehyde-3-phosphate is **2 ATP**.

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