A-Level Biology: Link Reaction and Krebs Cycle

Overview

• Part of aerobic respiration
• Glycolysis is the first stage (anaerobic and aerobic)
• Link Reaction and Krebs Cycle occur in the mitochondrial matrix

Link Reaction

• Transfer to Mitochondrial Matrix
  • Products from glycolysis (pyruvate and NADH) transported from cytoplasm
  • NADH used later in oxidative phosphorylation
• Process
  • Pyruvate is oxidized to acetate
  • Hydrogen from pyruvate is picked up by NAD to form NADH
  • Acetate (2-carbons) formed from pyruvate (3-carbons), releasing CO2
  • Acetate combines with coenzyme A to form acetyl Coenzyme A
• Products
  • Acetyl Coenzyme A, CO2, reduced NAD
  • No ATP produced
  • For one glucose molecule, the Link Reaction occurs twice (2 pyruvates)

Krebs Cycle

• Acetyl Coenzyme A Entry
  • Combines with a 4-carbon molecule to form a 6-carbon molecule
  • Coenzyme A is released and reused
• Redox Reactions
  • Converts 6-carbon to 4-carbon, releasing 2 CO2
  • Produces ATP
  • NAD and FAD are reduced (gain H+ and electrons)
• Products for One Cycle
  • 3 reduced NAD, 1 reduced FAD, 1 ATP, 2 CO2
  • For one glucose molecule (2 acetyl Coenzyme A), cycle occurs twice
  • Multiply products by 2 for total per glucose molecule

Summary

• Both Link Reaction and Krebs Cycle occur in the mitochondrial matrix
• Krebs Cycle is also known as the Citric Acid Cycle
• Essential processes for aerobic respiration

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