Cellular Respiration and Fermentation

Vocabulary flashcards covering the mechanisms of aerobic respiration, oxidative and substrate-level phosphorylation, fermentation pathways, metabolic regulation, and alternative fuel catabolism.

Chemiosmotic Hypothesis

The hypothesis proposing that the linkage between the electron transport chain and ATP production is indirect, wherein the ETC generates a proton-motive force across the inner membrane that drives ATP synthesis.

ATP Synthase

A multi-part protein complex composed of a membrane-embedded base ($F_0$ unit) and a knob ($F_1$ unit) linked by a rotor; it uses the electrochemical gradient of protons flowing back into the mitochondrial matrix to synthesize $\text{ATP}$ from $\text{ADP} + \text{P}_i$.

Substrate-Level Phosphorylation

The production of $\text{ATP}$ occurring via the direct enzyme-catalyzed transfer of a phosphate group from an intermediate phosphorylated substrate to $\text{ADP}$, utilized in glycolysis and the citric acid cycle.

Fermentation

An anaerobic metabolic pathway that keeps glycolysis operating in the absence of oxygen by transferring electrons from $\text{NADH}$ to an internal organic acceptor, thereby recycling $\text{NAD}^+$ and yielding $2\,\text{ATP}$ per glucose.

Lactic Acid Fermentation

An anaerobic pathway occurring in animal muscle cells and certain bacteria where pyruvate directly accepts electrons from $\text{NADH}$ with no chemical intermediate, regenerating $\text{NAD}^+$ and producing lactate.

Alcohol Fermentation

An anaerobic pathway occurring in yeast where pyruvate is enzymatically converted into acetaldehyde and $\text{CO}_2$, and acetaldehyde subsequently accepts electrons from $\text{NADH}$ to yield ethanol and $\text{NAD}^+$.

Acetaldehyde

The two-carbon intermediate molecule produced during alcohol fermentation upon the decarboxylation of pyruvate; it acts as the terminal electron acceptor that oxidizes $\text{NADH}$ to form ethanol.

Phosphofructokinase (PFK)

A key regulatory enzyme of glycolysis that catalyzes the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate; it is subject to negative feedback inhibition by $\text{ATP}$ and activation by $\text{ADP}$.

$\beta$-Oxidation

The catabolic process that breaks down fatty acids into two-carbon acetyl groups, which then enter the citric acid cycle as acetyl-CoA.

Deamination

The removal of the amino group ($\text{NH}_3$) from amino acids, producing urea waste and allowing the remaining carbon backbone to be funneled into cellular respiration pathways.

Catabolic Pathways

Metabolic reactions that involve the breakdown of complex molecules into simpler components with the concurrent production of $\text{ATP}$.

Anabolic Pathways

Metabolic reactions that synthesize complex macromolecules (such as DNA, RNA, glycogen, starch, proteins, and phospholipids) from smaller precursors using energy.

Proton-Motive Force

The electrochemical potential energy created by pumping protons ($\text{H}^+$) from the mitochondrial matrix into the intermembrane space via the electron transport chain.

Hypoxia

An environmental or physiological deficiency of oxygen that stalls the mitochondrial electron transport chain, forcing cells or aquatic organisms to rely on anaerobic fermentation.