Cell 3/5

Mitochondrial Structure and Function

• Mitochondrial Features

  • Contains a small circular chromosome and its own genetic material.

  • Houses ribosomes and tRNAs in the matrix.

  • The pyruvate dehydrogenase in the matrix converts pyruvate to acetyl CoA and generates NADH.

• Location Correction

  • Clarified that key processes occur in the matrix, not in the membrane.

Transport Mechanisms of Pyruvate

• Pyruvate Characteristics

  • Pyruvate is generated in the cytosol as a hydrophilic molecule.

  • Cannot diffuse across the mitochondrial membrane on its own.

• Transport Mechanisms

  • Requires channels, pumps, or transporters for entrance into the mitochondria.

  • Porin Protein:

    • A doughnut-shaped protein forming holes in the membrane, allowing small molecules like pyruvate to diffuse into the intermembrane space.

    • Diffusion aided by concentration differences between the cytosol and intermembrane space.

Pyruvate and Acetyl CoA Conversion

• Entering the Matrix

  • Pyruvate enters the intermembrane space easily via porin.

  • Utilizes the proton pyruvate symporter to cross into the matrix.

• Conversion in the Matrix

  • Enzyme: Pyruvate dehydrogenase converts pyruvate into acetyl CoA.

  • Acetyl CoA then feeds into the citric acid cycle, generating carbon dioxide and high-energy electrons.

Glycolysis Regulation Points

• Key Regulatory Enzymes

  • Phosphofructokinase (PFK):

    • Third enzyme in glycolysis, crucial for regulating carbon flow through the pathway.

    • Inhibited by citrate, indicating abundance in carbon substrates.

    • ATP inhibits, while AMP activates PFK.

• Metabolic Rationale

  • High citrate levels signal enough carbon available, thus inhibiting glycolysis.

  • ATP indicates high energy status, while AMP signals low energy, providing feedback for regulation.

Sources of Acetyl CoA

• Multiple pathways contribute to acetyl CoA production:

  • Pyruvate conversion

  • Beta oxidation of fatty acids

  • Protein breakdown into amino acids.

Gluconeogenesis

• Gluconeogenesis Process

  • Synthesis of glucose, occurring when glucose levels are low.

  • Utilizes middle stages of glycolysis.

  • Involves converting fructose 1,6-bisphosphate back to fructose 6-phosphate via Fructose-1,6-bisphosphatase.

• Regulatory Control

  • Enzymes like PFK and Fructose-1,6-bisphosphatase are key to balancing glucose synthesis and breakdown, depending on cellular energy status (rich in ATP/citrate or low energy).

Anaerobic Metabolism

• Distinction

  • Aerobic environments (rich in oxygen) versus anaerobic environments (lack oxygen).

  • Examples of organisms: Aerobes (e.g., humans, trees) vs. Anaerobes (e.g., certain bacteria).

• Types of Anaerobes

  • Obligate Anaerobes: Survive only in an oxygen-free environment.

  • Facultative Anaerobes: Can grow with or without oxygen, utilizing oxygen when available (e.g., black plague bacteria).

Fermentation

• Purpose of Fermentation

  • Recycles NAD+ to allow glycolysis to continue under anaerobic conditions.

  • Two main types:

    • Alcoholic Fermentation: Converts pyruvate to ethanol and carbon dioxide, primarily in yeast.

    • Lactic Acid Fermentation: Converts pyruvate into lactic acid, occurring in muscle cells during intense exercise.

Understanding ATP Production

• Oxidative Phosphorylation

  • Process involving the electron transport chain and proton pumping to create a proton gradient for ATP synthesis.

  • Similarities to photosynthesis in proton motive force and ATP synthase function:

    • Both processes utilize electron transport chains to establish gradients which power ATP production.

• Proton Motive Force

  • Electrochemical gradient of protons essential for ATP synthesis via ATP synthase.

  • Critical to cellular energy generation.