Net Yield of Glycolysis: ATP, NADH and Pyruvate per Glucose

The net yield of glycolysis per glucose is 2 ATP, 2 NADH and 2 pyruvate. The gross yield is 4 ATP, but 2 ATP are spent in the first half, so the net is 2. Water and H⁺ also appear in the balanced equation, but the MCAT focuses on those three products.

The count

• Spent: 1 ATP at hexokinase and 1 ATP at PFK-1, so 2 ATP.
• Made: 2 ATP per three-carbon piece at phosphoglycerate kinase and pyruvate kinase. There are two pieces, so 4 ATP.
• Net ATP: 4 made minus 2 spent = 2.
• NADH: one NADH per three-carbon piece at GAPDH, so 2.
• Pyruvate: one glucose splits into two three-carbon molecules, so 2.

What happens next depends on oxygen

• With oxygen (aerobic): pyruvate enters the mitochondria, and the 2 NADH can pass electrons to the electron transport chain. Textbooks vary in how many ATP they credit per cytosolic NADH, because the shuttle used decides how many electrons reach the chain. Use the number your passage or course gives.
• Without oxygen (anaerobic): NADH must be turned back into NAD⁺ or glycolysis stops. Fermentation does this by reducing pyruvate to lactate in animals, or to ethanol and CO₂ in yeast. Fermentation adds no ATP, so the net stays at 2 ATP per glucose.

Why NAD⁺ matters

GAPDH needs NAD⁺ as a substrate. If NAD⁺ runs out, step 6 stops and so does the payoff phase. That is the real reason fermentation exists: it regenerates NAD⁺, not ATP.

Quick variants

• Per pyruvate, not per glucose: halve everything. 1 ATP net, 1 NADH.
• Gross vs net: 4 ATP gross, 2 ATP net.
• Starting from glycogen: the first investment step is skipped in some pathways, so net ATP can differ. Check the question.
• Fructose or galactose entry: these enter at different points, so check which investment steps are skipped.

Common traps

• Answering 4 ATP. That is gross.
• Forgetting the doubling. Payoff steps happen twice per glucose.
• Saying fermentation makes ATP. It regenerates NAD⁺.
• Mixing up glycolysis and whole-glucose oxidation totals. Glycolysis alone is 2 ATP net.

One-minute recap

• Net per glucose: 2 ATP, 2 NADH, 2 pyruvate.
• Gross ATP is 4; investment is 2.
• Without oxygen, fermentation regenerates NAD⁺ and adds no ATP.