Cell Respiration (HL)

Role of Coenzymes

• NAD: Carrier of hydrogen, oxidized during respiration.
• ATP: Immediate energy source, released upon hydrolysis to ADP.

Glycolysis

• Conversion of glucose to pyruvate with ATP and reduced NAD production.
• Two ATP consumed, four produced (net gain of two ATP).

Anaerobic Respiration

• Partial breakdown of glucose to pyruvate, occurs in cytosol.
• Produces 2 ATP via substrate level phosphorylation.
• Fermentation: Converts pyruvate to lactate (in animals) or ethanol and CO2 (in plants/yeast), regenerating NAD.

Aerobic Respiration

• Complete breakdown of glucose to CO2 and H2O, requires mitochondria and oxygen.
• Involves:
  • Link Reaction: Pyruvate to acetyl CoA, CO2 released.
  • Krebs Cycle: Acetyl CoA to CO2, produces ATP and hydrogen carriers (NADH, FADH2).
  • Electron Transport Chain: Hydrogen carriers produce ATP via oxidative phosphorylation.

Energy Conversion

• Organic molecules store energy, transferred to ATP and hydrogen carriers.
• ATP Synthesis: Directly via substrate level phosphorylation or indirectly via oxidative phosphorylation (needs O2).

Mitochondria

• Site of aerobic respiration, evolved via endosymbiosis.
• Contains circular DNA, 70S ribosomes, double membrane.
• Matrix: Location of Krebs cycle.
• Cristae: Site of electron transport chain, increases surface area for optimized electron transport.

Electron Transport Chain and Chemiosmosis

• Hydrogen carriers unload protons and electrons in the matrix.
• Energy from electrons pumps protons into intermembrane space, creating an electrochemical gradient.
• Protons return via ATP synthase, catalyzing ATP synthesis (chemiosmosis).
• Oxygen is the terminal electron acceptor, forming water.

Differences in Energy Sources

• Carbohydrates: Easy to digest and transport, used in aerobic/anaerobic respiration.
• Lipids: Used aerobically, produce more energy per gram. Broken into 2C compounds forming acetyl CoA.

Summary

• Cell respiration transfers stored energy from organic molecules into coenzymes like ATP and NADH.
• Both aerobic and anaerobic pathways start with glycolysis but differ in their use of oxygen and location within the cell.