How many ATP and NADH are produced during the glycolytic pathway for each molecule of glucose?
The correct answer and explanation is:
During glycolysis, the breakdown of one molecule of glucose results in the production of 2 ATP molecules and 2 NADH molecules. Here is a breakdown of the process:
- ATP Consumption: In the early steps of glycolysis, glucose is phosphorylated twice, consuming 2 ATP molecules. First, glucose is converted into glucose-6-phosphate, using 1 ATP. Then, fructose-6-phosphate is phosphorylated to fructose-1,6-bisphosphate, consuming a second ATP. These steps are essential for activating the glucose molecule to enable further breakdown.
- Cleavage: Fructose-1,6-bisphosphate is split into two three-carbon molecules: dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. Dihydroxyacetone phosphate is quickly converted into another molecule of glyceraldehyde-3-phosphate. Now, two molecules of glyceraldehyde-3-phosphate will undergo the subsequent reactions of glycolysis.
- ATP Production: In the later stages of glycolysis, ATP is generated. Each glyceraldehyde-3-phosphate molecule is oxidized by NAD+ to produce 1 NADH. Then, each molecule of glyceraldehyde-3-phosphate is converted into 1,3-bisphosphoglycerate, which generates 2 ATP molecules via substrate-level phosphorylation. Since there are two molecules of glyceraldehyde-3-phosphate, the total ATP production from this step is 4 ATP.
- Net ATP: Although 2 ATP molecules are consumed in the first half of glycolysis, 4 ATP molecules are produced in the second half. The net ATP gain per glucose molecule is 2 ATP (4 ATP produced – 2 ATP consumed).
- NADH Production: During the oxidation of glyceraldehyde-3-phosphate, each molecule generates 1 NADH, so for two molecules of glyceraldehyde-3-phosphate, 2 NADH molecules are produced in total.
In summary, glycolysis yields 2 ATP and 2 NADH per molecule of glucose, with NADH carrying high-energy electrons to be used later in the electron transport chain during oxidative phosphorylation.