Summary of Glycolysis, Link Reaction, and Krebs Cycle

Introduction

• Overview of breaking down glucose through glycolysis, link reaction, and Krebs cycle.
• Aim: Understand the transformation of the six-carbon glucose molecule into carbon dioxide and its role in cellular respiration.

Glycolysis

• Location: Cytoplasm
• Initial Step: Glucose is phosphorylated by 2 ATP.
  • Phosphorylation adds phosphate groups to glucose, creating fructose 1,6-bisphosphate.
  • Makes glucose more reactive.
• Breakdown:
  • Fructose 1,6-bisphosphate splits into two triose phosphate molecules.
  • Triose phosphates yield 4 ATP through substrate-level phosphorylation.
  • Undergoes dehydrogenation, releasing hydrogen.
    • Hydrogen accepted by NAD, forming 2 reduced NADs.
• End Product: Pyruvate

Link Reaction

• Location: Mitochondrial Matrix
• Pyruvate Conversion:
  • Pyruvate undergoes decarboxylation, releasing CO2.
  • Forms a two-carbon molecule, which undergoes further dehydrogenation.
    • Hydrogen accepted by NAD, forming 2 reduced NADs.
  • Produces acetyl group, which combines with coenzyme A to form acetyl CoA.
• End Product: Acetyl CoA

Krebs Cycle (Citric Acid Cycle)

• Location: Mitochondrial Matrix
• Initial Step:
  • Acetyl CoA combines with oxaloacetate (4-carbon) to form citrate (6-carbon).
  • Coenzyme A is released and can transport other acetyl groups.
• Cycle Progression:
  • Citrate undergoes decarboxylation and dehydrogenation.
    • Produces CO2 and 2 reduced NADs.
    • Converts to a 5-carbon molecule.
  • Further decarboxylation and dehydrogenation of the 5-carbon molecule.
    • Produces CO2, 2 reduced NADs.
    • Results in a 4-carbon molecule.
  • 4-carbon molecule undergoes substrate-level phosphorylation.
    • Produces 2 ATP.
  • Further dehydrogenation forms 2 reduced FADs and 2 reduced NADs.
  • Oxaloacetate is regenerated.

Conclusion

• Glucose Breakdown:
  • Complete breakdown of glucose (6-carbon) into CO2.
  • Six molecules of CO2 are produced.
• Energy Production:
  • Total from the glucose breakdown: 6 ATP, 10 reduced NADs, and 2 reduced FADs.
• Future Topics:
  • Discussion on the role of reduced NADs and FADs in chemiosmosis and ATP synthesis.