Cellular Respiration and ATP Production

Electron Transport Chain (ETC)

  • The Electron Transport Chain is critical for ATP production in cellular respiration.
    • It oxidizes electron carriers, NADH and FADH₂, releasing energy at each step.
    • Each step in the pathway involves proteins called cytochromes.
  • At each cytochrome step:
    • High energy molecules are oxidized.
    • ATP is formed from ADP through phosphorylation.
    • H⁺ ions are generated, creating an electrochemical gradient across the mitochondrial membrane.
  • Final Electron Acceptor:
    • Oxygen (O₂) acts as the final electron acceptor in the chain.
    • It accepts electrons and combines with H⁺ ions to form water (H₂O).

Roles in Cellular Respiration

Glycolysis
  • Reactants: 1 glucose molecule
  • Products: 2 pyruvate, 2 NADH, and a net gain of 2 ATP.
Kreb's Cycle (Citric Acid Cycle)
  • Each glucose leads to:
    • 2 cycles (one for each pyruvate)
    • Products per cycle:
    • 3 NADH
    • 1 FADH₂
    • 1 ATP
    • 2 CO₂ (waste product)
ATP Calculation

  • Aerobic Respiration (with O₂):

    • Total ATP yield from the complete oxidation of 1 glucose:
    • Glycolysis: 2 ATP + 2 NADH (equivalent to 6 ATP with 3 ATP/NADH)
    • Kreb's Cycle (2 turns): 2 ATP + 6 NADH (equivalent to 18 ATP) + 2 FADH₂ (equivalent to 4 ATP)
    • Total: 2 (glycolysis) + 18 (Kreb's) + 4 (FADH₂) + 2 (direct ATP) = 36 ATP

  • Anaerobic Respiration (without O₂):

    • Only glycolysis occurs:
    • 2 ATP are produced directly.
    • 2 NADH can convert to 2 lactate, yielding only 2 ATP.
    • Total: 2 ATP (direct) + 2 (from lactate oxidation) = 8 ATP total.

Summary of Product Outcomes

  • Aerobic Respiration (glucose + O₂ → CO₂ + H₂O + ATP): 36 ATP
  • Anaerobic Respiration (glucose → lactate): 2 ATP
  • Main byproducts of aerobic respiration, CO₂ and H₂O, are expelled from the organism.

Key Points to Remember

  • The maximum ATP production happens during aerobic respiration due to the efficient transfer of electrons through the ETC.
  • Understanding both aerobic and anaerobic pathways is crucial for grasping energy metabolism in cells.