IB Biology Topic 8: Metabolism, Respiration, and Photosynthesis

Overview

• Focus: Respiration, including mitochondria, glycolysis, the link reaction, the Krebs cycle, and oxidative phosphorylation.
• Prerequisite: Completion of Topic 2 video series for foundation in metabolism and respiration.

Respiration

• Definition: Cellular process to release energy as ATP from organic compounds.
• Types:
  • Aerobic Respiration: Includes glycolysis, the link reaction, Krebs cycle, and oxidative phosphorylation.
  • Anaerobic Respiration: Only involves glycolysis.

Aerobic vs. Anaerobic Respiration

• Anaerobic Respiration:
  • Involves glycolysis only.
• Aerobic Respiration:
  • Begins with glycolysis.
  • Includes three additional stages:
    • The link reaction
    • The Krebs cycle
    • Oxidative phosphorylation
  • Generates 34 more ATP molecules per glucose than anaerobic respiration.

Key Reactions: Reduction and Oxidation

• Reduction: Gain of electrons, hydrogen gain, or oxygen loss.
• Oxidation: Loss of electrons, hydrogen loss, or oxygen gain.

Mitochondria Structure

• Function: Site of aerobic respiration stages beyond glycolysis.
• Components:
  • Double membrane with intermembrane space.
  • Inner membrane with electron transport chain and cristae.
  • Matrix containing enzymes for reactions.
  • Own DNA and 70S ribosomes.

Glycolysis

• Location: Cytoplasm
• Process:
  • Conversion of glucose to two pyruvate molecules.
  • Involves four stages:
    • Phosphorylation of glucose using 2 ATP.
    • Splitting into two three-carbon molecules.
    • Oxidation forms NADH.
    • Dephosphorylation produces 2 ATP per pyruvate.
• Yield:
  • 2 NADH, 4 ATP (net gain of 2 ATP), and 2 pyruvates.

The Link Reaction

• Location: Mitochondrial matrix
• Process:
  • Pyruvate transported to matrix, requires 1 ATP each.
  • Oxidation of pyruvate forms NADH, decarboxylation releases CO2.
  • Forms acetyl molecules that combine with coenzyme A to form acetyl-CoA.
• Yield:
  • 2 CO2, 2 NADH, and 2 acetyl-CoA per glucose molecule.

The Krebs Cycle

• Location: Mitochondrial matrix
• Process:
  • Acetyl-CoA combines with four-carbon molecule to form six-carbon molecule.
  • Oxidation and decarboxylation produce NADH and CO2.
  • Further oxidation produces FADH2 and more NADH.
• Yield:
  • 2 ATP, multiple NADH, FADH2, and CO2 per glucose.

Oxidative Phosphorylation

• Role: Primary mechanism for ATP production in aerobic respiration.

Conclusion

• For detailed understanding and visualization, electron tomography provides 3D images of mitochondria, enhancing comprehension of mitochondrial function.