Mitochondria and the Electron Transport Chain

Mitochondrial Structure

• Outer Membrane: Contains large pores that allow chemical passage while excluding large proteins; relatively low complexity.
• Inner Membrane: Highly folded to increase surface area; exceptionally protein-dense to accommodate $ATP$ production machinery and the electron transport chain (ETS).
• Intermembrane Space: The narrow region between membranes where a high-concentration hydrogen ion ($H^+$) gradient is established, resulting in a low pH.
• Matrix: The central compartment encased by the inner membrane; site of the Citric Acid Cycle and pyruvate conversion.

The Electron Transport Chain (ETC) Mechanism

• Energy Transfer: Electrons from $NADH$ and $FADH_2$ are passed through protein complexes to provide energy for pumping $H^+$ ions from the matrix into the intermembrane space.
• Complex I ($NADH$ dehydrogenase complex): Removes electrons from $NADH$ and initiates $H^+$ pumping.
• Complex II: Specialized for stripping electrons from $FADH_2$; this step can be bypassed by electrons traveling from Complex I directly to Complex III.
• Complex III: Receives electrons as they move through the sequence of the electron transport system.