Understanding Cellular Respiration and Fermentation

Oct 15, 2024

Cellular Respiration and Fermentation

Introduction

  • Understanding cellular respiration and fermentation in biology.
  • Aim to simplify a complex topic through a story-like explanation.

Overview of Cellular Respiration

  • Mitochondria produce ATP (energy currency of the cell) using chemical energy from food.
  • Cellular respiration occurs in both eukaryotic and prokaryotic cells.
  • Main reactants: glucose and oxygen.
  • Main products: CO2, water, and ATP.

Structure of Mitochondrion

  • Outer Membrane: Outermost layer.
  • Inner Membrane: Contains protein complexes for cellular respiration.
  • Matrix: Inner fluid area where some steps occur.
  • Intermembrane Space: Space between inner and outer membranes.

ATP Synthase

  • A transmembrane enzyme located in the inner membrane.
  • Converts ADP and inorganic phosphate into ATP by utilizing a proton gradient.
  • Powered by protons diffusing back into the matrix, causing the rotary part of ATP synthase to spin.

Proton-Motive Force and Chemiosmosis

  • High concentration of protons in the intermembrane space creates a proton motive force.
  • Chemiosmosis: Movement of protons across the membrane through ATP synthase.

Electron Transport Chain (ETC)

  • Consists of complexes I, II, III, and IV located in the inner membrane.
  • Transfers electrons from NADH and FADH2 through the chain.
  • Electrons move spontaneously due to increasing electronegativity.
  • Ends with electrons reducing oxygen to water.

Oxidation and Reduction in Cellular Respiration

  • Glucose is oxidized to CO2.
  • Oxygen is reduced to water.

Complete Oxidation of Glucose

  • Process of transferring electrons from glucose to electron carriers (NAD+ and FAD).
  • Carriers transport electrons to the ETC to facilitate ATP production.

Phases of Cellular Respiration

  1. Glycolysis
    • Occurs in the cytoplasm.
    • Breaks down glucose into 2 pyruvates, yielding 2 ATP and 2 NADH.
  2. Pyruvate Oxidation
    • Converts pyruvate into acetyl CoA, yielding NADH and CO2.
  3. Citric Acid Cycle (Krebs Cycle)
    • Occurs in the mitochondrial matrix.
    • Produces NADH, FADH2, ATP, and CO2.
  4. Oxidative Phosphorylation
    • Comprises the ETC and chemiosmosis.
    • Produces the bulk of ATP (28 ATP from one glucose molecule).

Net ATP Yield

  • Eukaryotes: 30 ATP per glucose.
  • Prokaryotes: 32 ATP per glucose (due to no mitochondrial transport cost).

Fermentation

  • Occurs when oxygen is unavailable (anaerobic conditions).
  • Glycolysis continues, producing 2 ATP per glucose.
  • Lactic Acid Fermentation: Converts pyruvate to lactic acid to regenerate NAD+.
  • Alcohol Fermentation: Occurs in yeast; converts pyruvate to ethanol and CO2.

Difference in Processes

  • Aerobic Respiration: Includes full cycle with oxygen as terminal electron acceptor.
  • Anaerobic Respiration: Uses a molecule other than oxygen as the terminal electron acceptor.
  • Fermentation: Only glycolysis occurs; pyruvate converted to lactic acid or ethanol.

Conclusion

  • Cellular respiration is crucial for ATP production and involves a series of redox reactions.
  • Understanding these processes explains biological phenomenons like breathing and weight loss.