Oxidative Phosphorylation Overview

Oxidative Phosphorylation

• Chemiosmotic Theory: Transmembrane differences in proton concentration are the energy source for biological oxidation-reduction reactions.

• General Steps:

  • Electron flow through a chain of membrane-bound carriers.
  • Free energy from this 'downhill' electron flow powers the 'uphill' transport of protons across a membrane.
  • Transmembrane proton flow through specific protein channels drives ATP synthesis.

• Oxidative Phosphorylation Process: Electrons enter the respiratory chain from catabolic pathways.

  • Dehydrogenases collect electrons.
  • Ubiquinone, cytochromes, and iron-sulfur proteins act as electron carriers.
  • Electrons are transferred sequentially, involving changes in oxidation states of iron (Fe3+ to Fe2+), hydrogen atoms (H+ + e-), and hydride ions(:H-).

Complexes I and II

• Complexes I and II transfer electrons to ubiquinone (Q) from NADH and succinate respectively.

• Complex III transfers electrons from reduced ubiquinone to cytochrome c.

• Complex IV completes electron transfer from cytochrome c to oxygen (O2).

Proton-Motive Force

• A proton gradient across the inner mitochondrial membrane is the proton-motive force.
• The difference is described as : ΔG = RT ln (C2/C1) + ZFAψ = 2.3RT ΔpH + FΔψ

Rotational Catalysis

• Conformational changes in ATP synthase are driven by proton passage.
• The y subunit of the Fo portion rotates in one direction during ATP synthesis and in the opposite direction during ATP hydrolysis.

ATP Yield from Complete Oxidation of Glucose

• Glycolysis: 2 NADH (cytoplasmic), 2 ATP. (Yield is 3 or 5 ATP for cytoplasmic NADH, depending on shuttle).

• Pyruvate oxidation (per glucose): 2 NADH (mitochondrial matrix). (Yield is 5 ATP).

• Citric Acid Cycle (per glucose): 6 NADH (mitochondrial matrix), 2 FADH2 , 2 ATP or 2 GTP (Yield is 15 or 18 ATP).

• Total Yield: 30 or 32 ATP. (Numbers vary based on shuttle system).

Insulin's Effects on Glucose and Lipid Metabolism

• Metabolic Effects: Insulin regulates blood glucose uptake; glycogen synthesis, glycolysis, and fatty acid synthesis.

• Target Enzymes: Processes like glucose transport, glucokinase, glycogen synthase, glycogen phosphorylase, and pyruvate dehydrogenase complex are impacted.

• Triacylglycerol Synthesis: Insulin promotes this process in adipose tissue.

Glucogenic Liver (Fasting State)

• Processes: Gluconeogenesis, glycogenolysis, ketone body formation, protein breakdown.
• Sources of Fuel: Liver uses amino acids, glycerol, and fatty acids to produce glucose and ketone bodies for other tissues.

Explore the intricate processes of oxidative phosphorylation, including the chemiosmotic theory and the roles of electron carriers. Understand how electron transfer contributes to ATP synthesis and learn about the function of complexes I and II in the respiratory chain.