- Transfers energy from electrons that move down it thru electron carriers that alternate between reduced and oxidized → released energy used to establish an electrochemical gradient of protons (H+) across the inner mitochondrial membrane
- Redox reactions needed for proton gradient
- Heat allows for hibernation; less ATP made but release heat better
- Carriers = proteins that act as primary electron acceptors
- Oxygen is ultimate electron acceptor with most affinity→ process needs oxygen
- Oxygen accepts electrons & protons → forms water
- NADH donates 2 electrons → oxidized, reverts back to NAD+, and goes back to glycolysis/krebs to do it all again
- If NADH couldn’t donate electrons → no glycolysis/Krebs/ETC; oxygen can’t accept electrons (not consumed); ATP levels drop
Chemiosmosis
- “Mechanism of ATP generation that occurs when energy is stored in the form of a proton concentration gradient across a membrane”
Couples electron transport and energy release to move protons down their energy gradient and through ATP synthase
- Krebs Cycle produces NADH and FADH2 in matrix
- Electrons are removed from NADH and FADH2
- Removed by protein complexes in the inner membrane → electrons move along ETC from one protein complex to another
- H+ ions (protons) are transported from the matrix to intermembrane space
- Electrons lose energy as they move down their electrochemical gradient thru redox reactions and complexes → complexes capture released energy to pump H+
- A proton gradient (proton motive force) and electrical gradient (voltage) is established across the inner membrane: represents potential energy
- As H+ are transferred, the concentration of H+ increases (pH decreases) in the intermembrane space and decreases in the matrix (pH increases).
- ATP synthase allows protons to flow back into the matrix (down gradient)
- The flow of protons back through ATP synthase by chemiosmosis generates energy for synthase to phosphorylate ADP to ATP
- Oxidative phosphorylation in cellular respiration
- Photophosphorylation in photosynthesis
The Proton Gradient
- Proton gradient = pH gradient = electrochemical (voltage) gradient = stored/potential energy
- Proton Motive Force: force exerted on protons by H+ gradient
The ATP Synthase enzyme
- Channel protein that translocates the hydrogen ions from high concentration to low concentration
- Cellular Respiration: From intermembrane to matrix
- Photosynthesis: from thylakoid lumen to stroma
- Protons move onto binding sites on the rotor, making it spin in a way that catalyzes ATP
- The active sites in the enzyme create 34 ATP
Role of Oxygen and Anaerobic Respiration
- Last electron acceptor in ETC; accepts electrons and protons to form water
- Without oxygen…
- No electron acceptor so electrons can’t pass thru and no proton gradient established
- NADH and FADH cannot transfer electrons and H+ → NAD+ and FAD not made → stops the citric acid cycle and glycolysis → no new ATP made → death
- Anaerobic respiration used by prokaryotes in low oxygen; sulfate or nitrate as final e-acceptor