Cellular Energetics Notes

Electron Transport Chain and Chemiosmosis

• Electrons combine with hydrogen ions and oxygen to form water.
• Oxygen is the final electron acceptor.
• If oxygen is unavailable, electron transport stops; no hydrogen ions are pumped, and no ATP is produced.

ATP Synthase

• Hydrogen ions flow down their gradient through ATP synthase.
• ATP synthase uses the electrochemical gradient to phosphorylate ADP, forming ATP.
• Electrochemical gradients are used in photosynthesis and cellular respiration.
• Electrochemical gradient: potential energy via diffusion gradient and electric charge gradient across a membrane.

Chemiosmosis

• Chemiosmosis: energy-coupling mechanism, uses H+ gradient to drive cellular work (ATP synthesis).
• Electron transport chain + chemiosmosis = oxidative phosphorylation.
• ADP is phosphorylated, and oxygen is necessary for electron flow.

Fermentation

• Fermentation: ATP generated without oxygen; expands glycolysis.
• Glycolysis produces two net ATP molecules; NAD+ is the electron acceptor.
• Fermentation regenerates NAD+.

Alcohol Fermentation

• Pyruvate converted to ethanol, releasing $CO_2$ and oxidizing NADH to create NAD+.

Lactic Acid Fermentation

• Pyruvate reduced by NADH (NAD+ formed), lactate is the waste product.

Citric Acid Cycle

• The six original carbons in glucose are released as $CO_2$.
• Only a few ATP molecules are produced directly.
• Most energy held in electrons in NADH and $FADH_2$.

Oxidative Phosphorylation

• Chemiosmosis couples electron transport to ATP synthesis.

Electron Transport Chain

• Embedded in the inner mitochondrial membrane.
• Composed of transmembrane proteins (hydrogen pumps) and carrier molecules.
• Powered by electrons from NADH and $FADH_2$.
• Electron energy loss is used to pump protons across the inner membrane.