Glycolysis and Krebs Cycle

Glycolysis

• Begins with a glucose molecule (6-carbon).
• Splits in half to form 2 pyruvate molecules (3-carbons each).
• Occurs in the cytoplasm and can happen with or without oxygen.
• Net gain: 2 ATP and 2 NADH.

Diagrammatic Representation

• Depicts a eukaryotic cell with focus on mitochondria.
• Glycolysis occurs in the cytoplasm.

Krebs Cycle (Citric Acid Cycle)

• Takes place in the inner membrane space (matrix) of mitochondria.
• Steps involved after glycolysis:
  • Oxidation of Pyruvate: Prepares for Krebs Cycle. Produces Acetyl-CoA (2-carbons) and NADH.
  • Combining Acetyl-CoA with Oxaloacetic Acid: Forms citric acid (6-carbon).
  • Citric Acid Oxidation: Returns to oxaloacetic acid, producing CO2, NADH, FADH2, and ATP.

ATP Production Overview

• Glycolysis: 2 ATP
• Krebs Cycle and pyruvate oxidation: Net 2 ATP, 8 NADH, 2 FADH2.
• NADH and FADH2 proceed to Electron Transport Chain (ETC).

Total ATP Produced

• Per glucose molecule:
  • 4 ATP directly (2 from glycolysis, 2 from Krebs Cycle)
  • 10 NADH, each producing 3 ATP in ETC = 30 ATP
  • 2 FADH2, each producing 2 ATP in ETC = 4 ATP
• Total: 4 (direct) + 34 (ETC) = 38 ATP.

Importance of NADH and FADH2

• Inputs for the Electron Transport Chain (ETC).
• Through oxidation, lead to the most ATP production.

Cellular Respiration Flexibility

• Besides glucose, proteins and fats can be metabolized to enter the Krebs Cycle.
• Acetyl-CoA is a common intermediate for various catabolic pathways.

Practical Notes

• Theoretical max ATP yield: 38 ATP per glucose.
• Glycolysis occurs in cytoplasm; Krebs Cycle in mitochondrial matrix.
• Process enzyme-catalyzed and involves intermediate compounds.
• Important for understanding metabolic flexibility and bioenergetics.

Conclusion

• Series of biochemical steps crucial for energy production.
• Enzyme-catalyzed reactions ensure efficient ATP generation.
• Preparatory and cyclical phases are essential for cellular respiration.