Glycolysis Lecture Notes

Introduction to Glycolysis

• Definition: Glycolysis is the splitting of a glucose molecule into two molecules of pyruvate.
  • Glucose: a six-carbon sugar.
  • Pyruvate: each molecule is a three-carbon compound.
• Energy Production: Energy released during glycolysis is captured in the form of ATP and NADH.

Location and Overall Reaction

• Location: Cytosol of the cell.
• Net Reaction:
  • Reactants: Glucose, 2 NAD⁺, 2 ADP, and 2 inorganic phosphate ions.
  • Products: 2 pyruvate, 2 NADH, 2 hydrogen ions, 2 ATP, and 2 water molecules.
• Reduction Process: Conversion of NAD⁺ to NADH (adding hydrogen is reduction).

Phases of Glycolysis

• Investment Phase (Steps 1-5): ( have to buy first to sell for more later. In the case of glycolysis, you need to put in energy (-2ATP molecules) so you can get more out later) (the first phase is endothermic and consumes energy and the second phase will produce more energy than what was put in ( 4ATP molecules and 2NADH)
  • Energy Input: Requires 2 ATP molecules.
• Payoff Phase (Steps 6-10):
  • Energy Output: Produces 4 ATP and 2 NADH molecules.
  • Net Gain: 2 ATP and 2 NADH.

Detailed Steps of Glycolysis

Step 1: Phosphorylation of Glucose

• Reactant: Glucose
• Product: Glucose 6-phosphate (G6P)
• Enzyme: Hexokinase
  • Role: Transfers phosphate from ATP to glucose.
• Cofactor: Mg²⁺
• Reversibility: Irreversible (ΔG = -16.7 kJ/mol)

Step 2: Isomerization to Fructose

• Reactant: Glucose 6-phosphate
• Product: Fructose 6-phosphate
• Enzyme: Phosphohexose Isomerase
• Reversibility: Reversible (ΔG = +1.7 kJ/mol)

Step 3: Second Phosphorylation

• Reactant: Fructose 6-phosphate
• Product: Fructose 1,6-bisphosphate
• Enzyme: Phosphofructokinase 1 (PFK-1)
• Cofactor: Mg²⁺
• Reversibility: Irreversible (ΔG = -14.2 kJ/mol)

Step 4: Cleavage of Fructose 1,6-bisphosphate

• Products: Glyceraldehyde 3-phosphate (G3P), Dihydroxyacetone phosphate (DHAP)
• Enzyme: Aldolase
• Reversibility: Reversible

Step 5: Interconversion of Triose Phosphates

• Conversion: DHAP to G3P
• Enzyme: Triose Phosphate Isomerase
• Reversibility: Reversible

Step 6: Oxidation and Phosphorylation

• Reactant: G3P
• Product: 1,3-bisphosphoglycerate
• Enzyme: Glyceraldehyde 3-phosphate Dehydrogenase
• Reaction Type: Oxidation of G3P, reduction of NAD⁺ to NADH

Step 7: Phosphoryl Transfer

• Reactant: 1,3-bisphosphoglycerate
• Product: 3-phosphoglycerate
• Enzyme: Phosphoglycerate Kinase
• ATP Production: 2 ATP (substrate-level phosphorylation)

Step 8: Phosphate Group Transfer

• Reactant: 3-phosphoglycerate
• Product: 2-phosphoglycerate
• Enzyme: Phosphoglycerate Mutase

Step 9: Dehydration

• Reactant: 2-phosphoglycerate
• Product: Phosphoenolpyruvate (PEP)
• Enzyme: Enolase
• By-product: Water (H₂O)

Step 10: Final Phosphate Transfer

• Reactant: PEP
• Product: Pyruvate
• Enzyme: Pyruvate Kinase
• ATP Production: 2 ATP
• Reversibility: Irreversible

Conclusion

• Irreversible Steps: Steps 1, 3, 10
• Reversible Steps: Steps 2, 4, 5, 6, 7, 8, and 9
• Net ATP Gain: 2 ATP per glucose molecule

Additional Resources

• Encourage further learning through additional videos and materials on related topics.