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Metabolism

Glycolysis

The first step in glucose breakdown to produce energy.

Definition

Glycolysis is the metabolic pathway of glucose breakdown into pyruvate or lactate, producing 2 ATP molecules. It takes place in the cytoplasm of all cells.

How it works

Glycolysis is the rapid anaerobic pathway that fuels intense efforts. It produces only 2 ATP per glucose (vs 30-32 for the complete aerobic pathway). In aerobic conditions, pyruvate enters the mitochondria and fuels the Krebs cycle. In anaerobic conditions, it is converted to lactate, causing muscle acidosis.

Role

Break down glucose into rapidly accessible energy, first step of cellular respiration.

Examples

  • 100m sprint: anaerobic glycolysis
  • Light jogging: glycolysis + Krebs cycle
  • Brain: continuous glycolysis

Recommendations

Carbohydrates with a high glycemic index are useful before intense efforts to quickly fuel glycolysis.

Key takeaway

Glycolysis is rapid but inefficient — the aerobic pathway produces 15 times more ATP.

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