AP BIO NOTES (copy)

Overview of Cellular Respiration

1. Types of Respiration

  • Aerobic Respiration:

    • Oxygen Requirement: Requires oxygen as a reactant.

    • Energy Yield: Releases more energy through the complete oxidation of glucose; can produce up to 32 ATP per glucose molecule.

    • Process Locations: Takes place in the cytosol (glycolysis) and mitochondria (Krebs cycle and oxidative phosphorylation).

  • Anaerobic Respiration:

    • Oxygen Requirement: Does not require oxygen and uses other compounds as final electron acceptors (e.g., sulfate, nitrate).

    • Energy Yield: Produces less energy compared to aerobic respiration.

    • Examples: Includes fermentation processes, which regenerate NAD+ to allow glycolysis to continue.

2. Glycolysis

  • Location: Occurs in the cytosol.

  • Process:

    • Breaks down one 6-carbon glucose molecule into two 3-carbon pyruvate molecules.

    • Energy Input: Requires 2 ATP to initiate the process.

    • Energy Output: Produces 4 ATP (a net gain of 2 ATP).

    • Electron Carriers: Generates 2 NADH through reduction-oxidation reactions.

  • Result: Pyruvates enter the mitochondria for the next stages of respiration if oxygen is available.

3. Steps in Mitochondria

  • Transition Step:

    • Before entering the Krebs cycle, each pyruvate is converted to Acetyl CoA, producing 2 NADH and releasing 2 CO2.

4. Krebs Cycle (Citric Acid Cycle)

  • Location: Takes place in the mitochondrial matrix.

  • Process:

    • Acetyl CoA combines with oxaloacetate to form citrate.

    • Energy Output: Through a series of reactions, produces 3 NADH, 1 FADH2, and 1 ATP per Acetyl CoA (double for glucose).

5. Electron Transport Chain (ETC)

  • Location: Occurs in the inner mitochondrial membrane.

  • Process:

    • Involves the electron transport chain (ETC) where NADH and FADH2 donate electrons.

    • Final Electron Acceptor: O2, which is reduced to form water.

    • As electrons move through complexes I-IV, energy is released, creating a proton gradient across the inner membrane.

    • H+ ions flow back into the matrix through ATP synthase, driving ATP production (about 34 ATP per glucose).

    • Mechanism: ATP synthase undergoes a conformational change powered by the proton motive force, leading to phosphorylation of ADP to ATP.

6. Anaerobic Respiration and Fermentation

  • Fermentation:

    • Location: Cytosol; occurs when oxygen is not available.

    • Types:

      • Alcoholic Fermentation (e.g., in yeast): Converts pyruvate to ethanol and CO2.

      • Lactic Acid Fermentation (e.g., in muscles): Converts pyruvate to lactate.

    • Energy Yield: Produces 2 ATP from glycolysis but allows for regeneration of NAD+ so glycolysis can continue.

7. Substrates and Regulation

  • Fuel Sources: Carbohydrates, fats, and proteins can all enter cellular respiration at various points, with their monomers feeding into glycolysis or the Krebs cycle.

  • Regulation: Allosteric enzymes regulate the flow through glycolysis and the citric acid cycle, inhibited by high levels of ATP and citrate, and stimulated by AMP.