Glycolysis Lecture Notes

Definition of Glycolysis

• Glycolysis: process of splitting a glucose molecule.
• Glucose: a six-carbon molecule.
• Result: Two molecules of pyruvate (three-carbon each).
• Energy captured: In the form of ATP and NADH.

Net Reaction of Glycolysis

• Occurs in the cytosol of the cell.
• Reactants: Glucose, 2 NAD+, 2 ADP, 2 inorganic phosphate.
• Products: 2 Pyruvate, 2 NADH, 2 H+, 2 ATP, 2 water molecules.
• NAD+ to NADH: Reduction process (addition of hydrogen).

Two Phases of Glycolysis

• Phase 1 (Investment Phase): Steps 1-5
  • Requires energy input.
  • Uses 2 ATP molecules.
• Phase 2 (Payoff Phase): Steps 6-10
  • Produces energy.
  • Yields 4 ATP and 2 NADH (net gain of 2 ATP and 2 NADH).

Ten Steps of Glycolysis

Step 1: Phosphorylation of Glucose

• Reactant: Glucose.
• Product: Glucose 6-Phosphate (G6P).
• Enzyme: Hexokinase.
• Cofactor: Magnesium ion (Mg²⁺).
• Irreversible: ΔG' = -16.7 kJ/mol.

Step 2: Isomerization

• Reactant: G6P.
• Product: Fructose 6-Phosphate (F6P).
• Enzyme: Phosphohexose isomerase.
• Reversible: ΔG' = +1.7 kJ/mol.

Step 3: Phosphorylation of Fructose 6-Phosphate

• Reactant: F6P.
• Product: Fructose 1,6-bisphosphate.
• Enzyme: Phosphofructokinase (PFK1).
• Irreversible: ΔG' = -14.2 kJ/mol.

Step 4: Cleavage of Fructose 1,6-bisphosphate

• Products: Glyceraldehyde 3-phosphate (G3P) and Dihydroxyacetone phosphate (DHAP).
• Enzyme: Aldolase.
• Reversible: ΔG' = +23.8 kJ/mol.

Step 5: Isomerization of DHAP to G3P

• Reaction: DHAP to G3P.
• Enzyme: Triose phosphate isomerase.
• Reversible.

Step 6: Oxidation and Phosphate Addition

• Reactant: G3P.
• Product: 1,3-Bisphosphoglycerate.
• Enzyme: Glyceraldehyde 3-phosphate dehydrogenase.
• Produces: 2 NADH.

Step 7: ATP Formation

• Reactant: 1,3-Bisphosphoglycerate.
• Product: 3-Phosphoglycerate.
• Enzyme: Phosphoglycerate kinase.
• Produces 2 ATP.

Step 8: Phosphate Group Shift

• Reactant: 3-Phosphoglycerate.
• Product: 2-Phosphoglycerate.
• Enzyme: Phosphoglycerate mutase.

Step 9: Enol Formation

• Reactant: 2-Phosphoglycerate.
• Product: Phosphoenolpyruvate (PEP).
• Enzyme: Enolase.
• Results in loss of water.

Step 10: Final Step - Pyruvate Formation

• Reactant: PEP.
• Product: Pyruvate.
• Enzyme: Pyruvate kinase.
• Produces 2 ATP.

Summary

• Irreversible Steps: 1, 3, 10.
• Net Gain: 2 ATP, 2 NADH per glucose molecule.
• End Products: 2 Pyruvate, 2 H₂O.

The information above provides a detailed description and breakdown of the glycolysis process, highlighting the important steps, enzymes involved, energy changes, and the biochemical implications.