Chapter 9 - Cellular Respiration and Fermentation

Cellular Respiration and Fermentation

The processes of how cells take fuel and pull out energy to make ATP.

Glycolysis

Sugar-splitting stage of aerobic respiration that occurs in the cytosol outside the mitochondria.

Pyruvate Oxidation & Citric Acid Cycle

The second main stage of aerobic respiration taking place in the mitochondria to finish oxidizing fuel and release CO2.

Oxidative Phosphorylation

The third main stage of aerobic respiration where the vast majority of ATP is made by a molecular machine.

Oxidation

The loss of electrons.

Reduction

The gain of electrons.

Cellular Respiration

A process where electrons fall down an electron gradient to the final electron acceptor (oxygen) to release energy.

Anaerobic Respiration

Respiration that uses an Electron Transport Chain without oxygen at the end.

Fermentation

A partial breakdown of sugars that uses neither oxygen nor an Electron Transport Chain (essentially glycolysis on a loop).

Electron Transport Chain (ETC)

A series of protein complexes that breaks a big energy drop into smaller, manageable steps to harvest energy gently.

NAD+

A critical initial electron carrier and oxidizing agent that is reduced into NADH when dehydrogenases strip two high-energy electrons and a proton from fuel.

Substrate-Level Phosphorylation

A mode of ATP synthesis where an enzyme grabs a phosphate group from a high-energy organic molecule and puts it on ADP.

Oxidative Phosphorylation (Mechanism)

ATP production powered by redox reactions in the electron transport chain, making almost 90% of the ATP.

Energy-Investment Phase (Glycolysis)

The phase where the cell invests 2 ATP molecules (such as hexokinase using ATP to stick a phosphate onto glucose).

Energy-Payoff Phase (Glycolysis)

The phase that generates 4 ATP from substrate-level phosphorylation and reduces 2 NAD+ to 2 NADH (net gain of 2 ATP and 2 NADH).

Pyruvate Processing

When pyruvate moves to the mitochondria and is processed by an enzyme complex into Acetyl CoA, releasing CO2 and reducing NAD+.

Citric Acid Cycle (Krebs Cycle)

The "metabolic furnace" loop that completes the oxidation of fuel, generating 3 NADH, 1 FADH2, and 1 ATP equivalent per Acetyl CoA.

Inner Mitochondrial Membrane

Folded into cristae to increase surface area, serving as the site for oxidative phosphorylation.

Ubiquinone and Cytochromes

Carriers that move electrons down the Electron Transport Chain.

Oxygen

The final electron acceptor at the bottom of the ETC that grabs electrons and protons to form water (H2O) as a final waste product.

Proton Motive Force

A massive concentration gradient of H+ ions built up by the ETC using energy from falling electrons.

ATP Synthase

A tiny rotary motor driven by the proton motive force that helps protons flow back down their gradient to power ATP generation.

Chemiosmosis

The process where the rotation of ATP Synthase transfers energy down a rod to change enzyme shape and convert ADP to ATP.

Alcohol Fermentation

A fermentation pathway where pyruvate releases CO2 and is reduced by NADH to ethanol, regenerating NAD+.

Lactic Acid Fermentation

A fermentation pathway without CO2 release where pyruvate is reduced by NADH to form lactate, regenerating NAD+.

Beta Oxidation

The process where fatty acids are chopped into two-carbon fragments that feed into the cycle as Acetyl CoA (yielding twice the ATP of carbohydrates).

Phosphofructokinase

The pacemaker enzyme in glycolysis (step three) regulated by ATP, citrate, and AMP levels to speed up or slow down cellular energy production.