Energy Production: Glycolysis and Krebs Cycle

Sep 15, 2024

Glycolysis and Krebs Cycle

Introduction

  • Glycolysis is a series of enzyme-catalyzed reactions that break down glucose into pyruvate.
  • Pyruvate is necessary for the Krebs cycle, which produces ATP, a high-energy molecule.

Glycolysis Process

  1. Starting Molecule
    • Begins with glucose, a 6-carbon sugar.
  2. Investment Phase
    • Investment of one ATP molecule to convert glucose into glucose 6-phosphate.
  3. Conversion Steps
    • Glucose 6-phosphate transforms into fructose 6-phosphate.
    • Another ATP converts fructose 6-phosphate to fructose 1,6-biphosphate.
    • Fructose 1,6-biphosphate breaks into DHAP and G3P.
    • DHAP is converted into G3P.
  4. Payoff Phase
    • G3P loses a hydrogen and two electrons to NAD+, forming NADH.
    • It gains an inorganic phosphate to become 1,3-biphosphoglycerate.
    • Loses a phosphate to ADP, forming ATP and phosphoglycerate.
    • Reorganizes into phosphenolpyruvate.
    • Phosphate removed to form ATP, resulting in pyruvate.

Transition to Krebs Cycle

  • Pyruvate enters the mitochondrial membrane.
  • Coenzyme A (CoA) is added to form acetyl-CoA.
  • Loses hydrogen, electrons to NAD+ (forming NADH), and CO2.
  • Acetyl-CoA enters the Krebs cycle.

Krebs Cycle

  1. Formation of Citrate
    • Acetyl group from acetyl-CoA combines with oxaloacetate.
    • Water is added, CoA is released to form citrate.
  2. Conversion Processes
    • Citrate rearranges to isocitrate.
    • Isocitrate loses hydrogen and electrons to NAD+ to form NADH, loses CO2 forming alpha-ketoglutarate.
    • Alpha-ketoglutarate loses hydrogen, electrons (forming NADH), CO2 and forms ATP.
    • Water added to form succinate, transformed into fumarate (produces FADH2).
    • Fumarate transforms to malate.
    • Malate loses hydrogen, electrons to NAD+, forming NADH and oxaloacetate.
  3. Cycle Continuation
    • Oxaloacetate is ready to start the cycle again.

Importance of NADH and FADH2

  • Produced NADH and FADH2 proceed to the electron transport chain.
  • The electron transport chain produces 34 ATP from these carriers.

Conclusion

  • Glycolysis and the Krebs cycle are crucial for energy production in the form of ATP.
  • These cycles are continuous as long as the organism is alive.