Mitochondria (lecture 8)

Mitochondria: Structure and Respiration - Key Notes

1. Introduction to Mitochondria

  • Mitochondria are the powerhouses of the cell, responsible for energy production.

  • They evolved from ancient bacteria through endosymbiosis.

  • Found in most eukaryotic cells, especially in high-energy cells like muscles and neurons.

2. Structure of Mitochondria

  • Double Membrane:

    • Outer Membrane: Permeable due to porins (allows small molecules to pass).

    • Inner Membrane: Highly folded into cristae to maximize ATP production.

  • Intermembrane Space: Between the inner and outer membrane.

  • Matrix: Contains mtDNA, ribosomes, and metabolic enzymes.

3. Functions of Mitochondria

  • Energy Metabolism:

    • TCA cycle (Krebs cycle) occurs in the matrix.

    • Oxidative phosphorylation occurs in the inner membrane.

    • Produces ATP via the electron transport chain (ETC).

  • Synthesis of essential molecules:

    • Amino acids, heme groups.

  • Calcium Ion Regulation:

    • Helps in cell signaling.

  • Redox Balance:

    • Prevents oxidative damage from reactive oxygen species (ROS).

  • Apoptosis Regulation:

    • Mitochondria play a key role in programmed cell death.

4. Cellular Respiration: Energy Production

  • Glycolysis (in cytosol):

    • Converts glucose → 2 pyruvate + 2 ATP + 2 NADH.

  • Pyruvate Oxidation:

    • Pyruvate enters mitochondria → converted into Acetyl-CoA.

  • TCA Cycle (Krebs Cycle) in the Matrix:

    • Acetyl-CoA enters, producing 3 NADH, 1 FADH₂, 1 GTP (ATP), and 2 CO₂ per cycle.

  • Electron Transport Chain (ETC) and ATP Synthesis:

    • NADH & FADH₂ donate electrons.

    • Oxygen is the final electron acceptor, forming H₂O.

    • ATP synthase generates ~36 ATP per glucose molecule.

5. Mitochondrial Inheritance and Disorders

  • Maternally Inherited:

    • mtDNA comes from the mother.

  • Mitochondrial Diseases:

    • Caused by mutations in mtDNA, affecting energy production.

    • Examples: Leigh’s Syndrome, Mitochondrial Myopathy.

  • Mitochondria and Aging:

    • ROS damage over time contributes to aging and age-related diseases.

6. Aerobic vs. Anaerobic Metabolism

  • Aerobic Respiration (with oxygen):

    • Produces high ATP yield (~36 ATP/glucose).

  • Anaerobic Respiration (without oxygen):

    • Produces lactic acid (in animals) or ethanol (in yeast).

    • Generates only 2 ATP per glucose.

7. Muscle Fiber Types and Energy Use

  • Fast-Twitch Fibers:

    • Use anaerobic respiration for quick energy bursts.

  • Slow-Twitch Fibers:

    • Use aerobic respiration for endurance