Mitochondria & Chemiosmosis

Overview of Mitochondria and Chemiosmosis

Learning Objectives

• Identify Key Features of Mitochondria
• Evaluate the Purpose of Chemiosmotic Coupling during oxidative phosphorylation.
• Describe Mechanisms of Electron Transport and Proton Pumping.

Purpose of Mitochondria

• Mitochondria are essential for energy production via oxidative phosphorylation and chemiosmosis.

Structure of the Mitochondrion

• Outer Membrane

  • Contains porins.
  • Permeable to small molecules (less than 5000 Da), e.g., typical proteins are around 50 kDa.

• Intermembrane Space

  • Chemically similar to cytosol.
  • Contains:
    • Proteins that initiate apoptosis.
    • ATP-dependent kinases.

• Matrix

  • Contains 2/3 of all mitochondrial enzymes.
  • Functions:
    • Beta oxidation (e.g., Fatty acids → Acetyl CoA).
    • Intermediate step (e.g., Pyruvate → Acetyl CoA).
    • Citric acid cycle (Krebs cycle).

• Inner Membrane

  • Folded into cristae, increasing surface area.
  • Site of oxidative phosphorylation, which includes:
    1. Electron Transport Chain (ETC)
    2. ATP Synthase
    • Contains many transporters essential for function.

Key Sources of Acetyl CoA

• Acetyl CoA is generated from:
  • Fatty acid oxidation.
  • Pyruvate resulting from glycolysis.

Endosymbiotic Theory

• Mitochondria exhibit similarities to bacteria, such as:
  • Circular DNA
  • Division involving binary fission.
  • Similar Ribosomes.

Location and Utilization of Mitochondria

• Mitochondria are strategically located near high ATP utilization sites:
  • Cardiac Muscle:
    • High energy demand; mitochondria border contractile apparatus.
  • Sperm:
    • Motility via flagella, thus have high ATP demands.
    • Mitochondria found along the flagellum tail.

Mitochondrial Networks

• Mitochondria can form elongated tubular networks which optimize energy production through electron transfer.

Chemiosmosis and ATP Production

• Stage 1: Chemiosmotic Potential

  • Activated carriers transfer electrons to ETC proteins.
  • Protons are pumped across the inner membrane, creating a proton gradient.

• Stage 2: ATP Generation

  • The generated chemiosmotic proton gradient drives ATP synthase to produce ATP.
  • Summary of processes:
    1. Citric acid cycle produces high-energy electrons.
    2. Activated carriers (NADH, FADH2) shuttle electrons to the ETC.
    3. Electron movement coupled to proton pumping across the inner mitochondrial membrane.
    4. This establishes a steep electrochemical gradient.
    5. Chemiosmotic gradient drives ATP synthesis via ATP synthase.