POB8--Cellular_Respiration

Chapter 6: Cellular Respiration

Overview of Energy in Food

  • Energy obtained from breaking down organic molecules (e.g., sugar) produced in plants.

    • Heat energy from ATP and reducing power from NADPH invested to build glucose.

    • Glucose represents potential energy.

    • Cellular respiration is the oxidation of food molecules to obtain energy.

Metabolism

  • Metabolism encompasses all chemical reactions in a biological system.

    • Anabolic Reactions: Build complex molecules (anabolism).

    • Catabolic Reactions: Break down molecules for energy (catabolism).

Aerobic Cellular Respiration

  • Requires oxygen; chemical reaction: C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + energy (heat or ATP).

  • Products: carbon dioxide, water, and energy, inverse to photosynthesis.

Steps in Cellular Respiration

  1. Glycolysis

    • Occurs in the cytoplasm; does not require oxygen.

    • Breaks down glucose (6 carbon) into two pyruvate (3 carbon).

    • Produces a small amount of ATP via substrate-level phosphorylation.

    • Transfers electrons and hydrogen to NAD+ forming NADH.

  2. Krebs Cycle (Citric Acid Cycle)

    • Takes place in mitochondrion and processes acetyl-CoA.

    • Involves:

      • Carbon removal (as CO₂).

      • Formation of NADH and FADH₂ from oxidation reactions.

      • Production of ATP.

    • Two turns for each glucose (as it produces two pyruvate).

  3. Electron Transport Chain (ETS)

    • Utilizes electrons from NADH and FADH₂.

    • Electrons drive proton pumps, creating a gradient.

    • Last stage donates electrons to oxygen, forming water.

    • Oxygen is essential for oxydative respiration.

Chemiosmosis

  • Coupled with ETS; protons pumped into intermembrane space.

  • Protons flow back into matrix through ATP synthase, driving ATP synthesis.

ATP Production Summary

  • Total ATP Yield from Oxidative Respiration: 36 ATP molecules

    • From Glycolysis: 2 ATP

    • From Krebs Cycle: 2 ATP

    • Through Electron Transport: 32 ATP

Anaerobic Respiration

  • In absence of oxygen, relies solely on glycolysis.

  • Fermentation process regenerates NAD+ by donating H from NADH to organic molecules.

    • Types of Fermentation:

      • Yeast: converts pyruvate to acetaldehyde (producing ethanol).

      • Animals: converts pyruvate to lactate (producing lactic acid).

Alternative Food Sources

  • Cells can derive energy from other macromolecules:

    • Major macromolecules undergo modifications to enter cellular respiration.

    • Many metabolites plug into the Krebs cycle.