Electron Transport and Chemiosmosis

• NADH and FADH₂ carry electrons to the ETC
• Each become oxidized, losing two electrons to the ETC

The Electron Transport Chain (ETC) Structure

• Located within the inner mitochondrial membrane
• Composed of various protein structures arranged in order of increasing electronegativity
• Ex. weakest electron attractor (NADH dehydrogenase) is at the beginning of the chain and the strongest   (cytochrome oxidase) at the end

How it Works:

• Electrons pass from one component protein in the chain to the next
• As they move from molecule to molecule they occupy ever more stable position relative to the nuclei of the atoms they associate with;
• Free energy released in the process is used to move protons [H+ ions] from the mitochondrial matrix to the intermembrane space
• Electrons reaching the end of the chain are in very stable positions and require the extremely electronegative oxygen to remove them from the ETC

IMPORTANT:

• NAD+ and FAD+ are in limited supply and must be oxidized by the ETC to reuse them
• Electrons must be removed from the ETC by oxygen to keep the ETC working

NADH:

• Drops electrons off at first complex; moves 3 H⁺ ions; produces 3 ATP
• GLYCOLYSIS: NADH cannot penetrate the mitochondrial inner membrane, however a membrane shuttle transfers electrons from the glycolysis NADH to FAD to produce FADH₂
  

  

FADH₂:

• Drops electrons off at cytochrome Q; moves 2 H⁺ ions; produces 2 ATP

Chemiosmosis and Oxidative ATP Synthesis

• The intermembrane space is impermeable to H⁺ ions
• Pumping H⁺ ions out of the matrix and into them intermembrane space creates an electrochemical gradient
• Electron free energy is transferred to potential energy in the electrochemical gradient

Electrochemical gradient:

• Higher positive charge [H⁺ ions] in the intermembrane space than in the matrix
• Higher concentration of H⁺ ions in the intermembrane space than in the matrix

Proton-Motive Force (PMF):

• Created by the H⁺ ions desire to move away from each other because they repel one another (like charges) and the want to diffuse into the matrix (low H⁺ conc.)
• Causes H⁺ ions to move around in the intermembrane space

ATP Generation:

• Unable to move through the inner membrane, H⁺ ions are forced to move through special protein channels called ATP synthase
• Free energy of the electrochemical gradient drives the synthesis of ATP from ADP and P_i in the matrix; chemiosmosis