**ATP Synthesis in Glycolysis**

Glycolysis is the first step in cellular respiration, where glucose is converted into pyruvate. During this process, a small amount of ATP is directly synthesized. Let's break down the steps involved in glycolysis and calculate the number of ATP molecules produced from one molecule of glucose.

**Step 1: Phosphorylation of Glucose**
- In the first step, glucose is phosphorylated by ATP to form glucose-6-phosphate.
- One ATP molecule is used in this step to phosphorylate glucose.
- No ATP molecules are produced.

**Step 2: Conversion to Fructose-6-phosphate**
- Glucose-6-phosphate is then converted into fructose-6-phosphate.
- No ATP molecules are used or produced in this step.

**Step 3: Phosphorylation of Fructose-6-phosphate**
- Fructose-6-phosphate is phosphorylated by ATP to form fructose-1,6-bisphosphate.
- One ATP molecule is used in this step to phosphorylate fructose-6-phosphate.
- No ATP molecules are produced.

**Step 4: Cleavage of Fructose-1,6-bisphosphate**
- Fructose-1,6-bisphosphate is cleaved into two three-carbon molecules: dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P).
- No ATP molecules are used or produced in this step.

**Step 5: Interconversion of DHAP and G3P**
- DHAP is converted into G3P, which allows both molecules to continue through glycolysis.
- No ATP molecules are used or produced in this step.

**Step 6: Oxidation and ATP Formation**
- G3P undergoes oxidation, generating NADH and producing 1,3-bisphosphoglycerate.
- One NADH molecule is produced per G3P molecule.
- No ATP molecules are produced in this step.

**Step 7: Substrate-level Phosphorylation**
- 1,3-bisphosphoglycerate is converted into 3-phosphoglycerate, and ATP is directly synthesized.
- One ATP molecule is produced per 1,3-bisphosphoglycerate molecule.
- Two ATP molecules are produced from two 1,3-bisphosphoglycerate molecules.

**Step 8: Conversion to Pyruvate**
- 3-phosphoglycerate is converted into pyruvate, generating one ATP molecule per pyruvate molecule.
- Two ATP molecules are produced from two molecules of 3-phosphoglycerate.

**Overall ATP Production**
- In summary, during glycolysis, two ATP molecules are consumed in the initial steps (steps 1 and 3) to phosphorylate glucose and fructose-6-phosphate.
- A total of four ATP molecules are directly synthesized in the later steps (steps 7 and 8) from the intermediate molecules.
- Therefore, the net ATP production from one molecule of glucose in glycolysis is two ATP molecules.

In conclusion, the direct synthesis of ATP in glycolysis from one molecule of glucose yields a net production of two ATP molecules.

It starts with one molecule of glucose and end with two pyruvate molecules a total 4 ATP molecules and 2 molecules of NADH.
Glucose ↔glucose 6- phosphate ↔fructose 6 phosphate ↔fructose 1:6 biphosphate↔glyceraldehbyde 3 phosphate ↔ 2* 1:3 biphosphoglycerate ↔2* 3 phosphoglycerate ↔ 2*. 2 phosphoglycerate ↔2*. Phosphoenol pyruvate ↔ 2*. Pyruvate