Lecture Notes: Glycolysis in Biochemistry

Key Concepts

• Glycolysis is a biochemical pathway that starts with glucose and ends with pyruvate.
• It occurs in the cytoplasm of the cell, unlike the electron transport chain and Krebs cycle which occur in the mitochondria.
• Glycolysis operates independently of oxygen availability.

Why Glycolysis Occurs in the Cytoplasm

• Location is important because it allows glycolysis to function without dependence on oxygen.
• Glycolysis will run regardless of other cellular processes, such as electron transport or Krebs cycle.

Glycolysis Pathway Overview

• Glycolysis results in the formation of two pyruvate molecules from one glucose molecule.
• There are several key steps and reactions involving ATP and various substrates.

Steps of Glycolysis

1. Initial Step: Glucose Transport

   • Glucose is transported into the cell using glucose transporters and is phosphorylated to form glucose 6-phosphate, trapping it inside the cell.
   • Consumes 1 ATP

2. Conversion to Fructose 6-Phosphate

   • Glucose is converted from an aldose to a ketose form.
   • No energy is used in this conversion.

3. Formation of Fructose 1,6-Diphosphate

   • Fructose 6-phosphate is phosphorylated, consuming another ATP.
   • Ensures glucose derivatives remain in the cell.

4. Cleavage by Aldolase

   • Splits fructose 1,6-diphosphate into two 3-carbon molecules: dihydroxyacetone phosphate and glyceraldehyde 3-phosphate.
   • Both can’t leave the cell due to attached phosphate groups.

5. Glyceraldehyde 3-Phosphate Oxidation

   • Glyceraldehyde 3-phosphate is oxidized to a carboxylic acid, forming NADH and attaching another phosphate group.

6. ATP Formation

   • ATP is produced from substrate-level phosphorylation.
   • Initial ATP investment is now balanced (2 ATP consumed, 2 ATP produced).

7. Formation of High-Energy Intermediates and Further ATP Production

   • The pathway continues to rearrange molecules and produces more ATP.
   • Final ATP yield from substrate-level phosphorylation is net zero, but NADH can contribute additional ATP if oxygen is present.

Net Energy Yield

• In Anaerobic Conditions:

  • Net gain of 2 ATP from glycolysis.

• In Aerobic Conditions:

  • NADH contributes to electron transport chain, forming additional ATP.
  • Total net gain can be 8 ATP per glucose if oxygen is present.

Conclusion and Next Steps

• Understand the glycolysis process and its ATP yield.
• The following lecture will cover the conversion of pyruvate to acetyl-CoA and the full ATP yield under aerobic conditions.

Additional Notes

• Review this video and print the metabolic cycle diagrams provided.
• Reach out during office hours for further clarification.
• The importance of glycolysis in both aerobic and anaerobic conditions, despite the dependency of other pathways on oxygen.

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Recommended Actions:

• Watch the video again to solidify understanding.
• Use provided diagrams to fill in steps and visualize glycolysis.
• Prepare questions for office hours if needed.