ATP Production in Aerobic Cellular Respiration

Glycolysis

• Takes place in the cytoplasm of the cell.
• Glucose is broken down into 2 pyruvate molecules.
• Generates:
  • 2 ATP molecules.
  • 2 NADH molecules.
• ATP can be used directly by the cell; NADH must be transported to the electron transport chain (ETC).

Electron Transport Chain and NADH Shuttles

Glycerol 3-Phosphate Shuttle

• Used by cells such as skeletal muscle cells.
• High-energy electrons are transported to complex III of the ETC.
• Bypasses complex I.
• Produces 1.5 ATP per NADH.
• For 2 NADH: 2 x 1.5 = 3 ATP.

Malate-Aspartate Shuttle

• Used by cells such as cardiac muscle cells and liver cells.
• High-energy electrons are transported to complex I of the ETC.
• Produces 2.5 ATP per NADH.
• For 2 NADH: 2 x 2.5 = 5 ATP.

Pyruvate Decarboxylation

• Takes place in the matrix of the mitochondria.
• 2 pyruvate molecules are transformed into 2 acetyl CoA molecules.
• Generates 2 NADH molecules.
• Each NADH produces 2.5 ATP.
• Total for 2 NADH: 2 x 2.5 = 5 ATP.

Citric Acid Cycle (Krebs Cycle)

• Acetyl CoA molecules are fed into the citric acid cycle.
• Generates:
  • 2 GTP (converted to 2 ATP).
  • 6 NADH (each NADH produces 2.5 ATP: 6 x 2.5 = 15 ATP).
  • 2 FADH2 (each FADH2 produces 1.5 ATP: 2 x 1.5 = 3 ATP).

Total ATP Production from One Glucose Molecule

• Glycolysis: 2 ATP + NADH via ETC = 3 to 5 ATP (depending on shuttle used).
• Pyruvate Decarboxylation: 5 ATP.
• Citric Acid Cycle: 2 + 15 + 3 = 20 ATP.
• Total ATP:
  • Using Glycerol 3-Phosphate Shuttle: 2 + 3 + 5 + 20 = 30 ATP.
  • Using Malate-Aspartate Shuttle: 2 + 5 + 5 + 20 = 32 ATP.