12.03 Glycolysis

Definition

• Glycolysis: The breakdown (lysis) of glucose (6C) into two molecules of pyruvate (3C), taking place in the cytoplasm.

Overview of Glycolysis Stages

1. Initial Phosphorylation

• ATP Investment: Uses 2 ATP molecules to add phosphate groups to glucose.
• Steps:
  • Glucose (6C) → Glucose Phosphate → Fructose Phosphate → Fructose 1,6 Bisphosphate.
• Result: Fructose 1,6 bisphosphate (6C) splits into 2 triose phosphate molecules (3C).

1. Oxidation of Triose Phosphate

• Hydrogen Removal: Hydrogen is removed from each triose phosphate, reducing NAD to reduced NAD (NADH).
• Oxidation: Triose phosphate is oxidized, and NAD is reduced by gaining hydrogen.
• Products per Glucose: 2 NADH molecules.

1. ATP Production via Substrate-Linked Phosphorylation

• Direct ATP Formation: Phosphate groups from intermediate molecules in glycolysis are transferred to ADP to form ATP (example of substrate-linked phosphorylation).
• Net ATP Gain:
  • 4 ATP produced minus 2 ATP used initially = Net gain of 2 ATP per glucose.

End Product: Pyruvate

• Pyruvate (3C): Contains significant chemical potential energy.
• Transport to Mitochondria:
  • If oxygen is available, pyruvate is actively transported into the mitochondrial matrix for further breakdown in aerobic respiration (requires a small amount of ATP).

Key Points

• Net Products of Glycolysis per Glucose:
  • 2 Pyruvate
  • 2 ATP (net)
  • 2 NADH
• Location: Entire process occurs in the cytoplasm