Direct phosphoryaltion in glycolytic pathway of respiration.

Options

A. Occurs when 2H atoms are removed from gylceraldehyde 3-phosphate
B. Needs enzyme pyruvate kinase only
C. Occurs when triose biphosphate is dephosphorylated to triose phosphate
D. Produces a total of 2 molecules of ATP per glucose

Answer

### Step-by-Step Solution:

1. **Understanding Glycolysis**:
- Glycolysis is the first step in the process of cellular respiration. It involves the breakdown of glucose (a six-carbon sugar) into two molecules of pyruvate (a three-carbon compound).
- The term "glycolysis" comes from "glyco-" meaning glucose and "-lysis" meaning breakdown.

2. **Direct Phosphorylation in Glycolysis**:
- In glycolysis, ATP is produced through a process known as substrate-level phosphorylation, which is a form of direct phosphorylation.
- This occurs in specific steps of glycolysis where a phosphate group is directly transferred from a substrate to ADP to form ATP.

3. **Key Reactions Involved**:
- During glycolysis, there are several key reactions that lead to ATP production:
- One important reaction involves the conversion of phosphoenolpyruvate (PEP) to pyruvate, catalyzed by the enzyme pyruvate kinase. This reaction produces ATP from ADP.
- Another reaction involves the conversion of glyceraldehyde-3-phosphate (G3P) to 1,3-bisphosphoglycerate, which is coupled with the reduction of NAD+ to NADH.

4. **ATP Investment and Yield**:
- Glycolysis requires an initial investment of 2 ATP molecules to activate glucose.
- However, through the subsequent reactions, a total of 4 ATP molecules are produced.
- Therefore, the net gain of ATP from glycolysis is 4 ATP produced minus 2 ATP invested, resulting in a net production of 2 ATP molecules per glucose molecule.

5. **Conclusion**:
- The process of glycolysis results in the direct synthesis of ATP through substrate-level phosphorylation, specifically during the conversion of PEP to pyruvate.
- Overall, glycolysis yields a net gain of 2 ATP molecules for each molecule of glucose that is metabolized.