Lecture Notes: Cellular Respiration

Pyruvate Oxidation

• Occurs when oxygen is present; pyruvate enters the mitochondria.
• Pyruvate is oxidized into acetyl-CoA.
  • Acetyl-CoA is crucial for the citric acid cycle as it forms citrate.
• Outputs of pyruvate oxidation:
  • 2 CO2
  • 2 NADH

Citric Acid Cycle (Krebs Cycle)

• Takes place in the mitochondrial matrix.
• Converts acetyl-CoA into citrate.
• Outputs per glucose molecule:
  • 2 ATP
  • NADH and FADH2
  • Release of CO2
• Main functions:
  • Synthesis of ATP
  • Transfer of electrons to NADH and FADH2
• No need to memorize intermediates; focus on inputs and outputs.

Oxidative Phosphorylation

• Consists of the Electron Transport Chain (ETC) and chemiosmosis.
• Occurs in the inner mitochondrial membrane.

Electron Transport Chain (ETC)

• Proteins embedded in the membrane transfer electrons through redox reactions.
• Increases surface area via cristae for reactions.
• Manages energy release through stepwise electron transfer.
• Oxygen is the final electron acceptor, forming water with hydrogen ions and electrons.
• If oxygen is blocked (e.g., by cyanide), the ETC shuts down, stopping cellular respiration.

Chemiosmosis

• Powered by the proton gradient created by the ETC.
• Hydrogen ions flow through ATP synthase, converting ADP to ATP.
• Major ATP production site, yielding 26-28 ATP per glucose.

Key Concepts

1. Proton Gradient Formation:
   • Created across the inner mitochondrial membrane by the flow of electrons from NADH and FADH2 powering the ETC complexes to pump hydrogen ions.
2. Final Electron Acceptor:
   • Oxygen, essential for ETC functionality.
3. ATP Synthase Energy Source:
   • Uses the proton gradient to convert ADP + P to ATP.

Summary

• Cellular respiration stages:
  • Glycolysis, Pyruvate Oxidation, Citric Acid Cycle, Oxidative Phosphorylation.
• Total ATP production: 30-32 ATP per glucose.