Fermentation, Cellular Respiration, and Mitochondria

Vocabulary practice flashcards covering fermentation, cellular respiration pathways, organelle locations, endosymbiotic theory, and related metabolic case studies.

Glycolysis

A cytoplasmic metabolic pathway occurring in both eukaryotes and prokaryotes that breaks down glucose into $2$ pyruvate molecules, producing a net gain of $2\text{ ATP}$ via substrate-level phosphorylation and reducing $\text{NAD}^+$ to $2\text{ NADH}$.

Fermentation

A cytoplasmic pathway that regenerates $\text{NAD}^+$ in the absence of cellular respiration by transferring electrons from $\text{NADH}$ to an organic molecule, operating without an electron transport chain and producing no ATP directly.

Alcohol (Ethanol) Fermentation

A fermentation pathway occurring in yeast where pyruvate releases $\text{CO}_2$ to form acetaldehyde, which is subsequently reduced by $\text{NADH}$ to ethanol, regenerating $\text{NAD}^+$.

Lactic Acid Fermentation

A fermentation pathway occurring in mammalian muscle cells during oxygen deficits and in many tumor cells where pyruvate is directly reduced by $\text{NADH}$ to lactate (lactic acid) without releasing $\text{CO}_2$, regenerating $\text{NAD}^+$.

$$\text{NAD}^+$$

An essential electron carrier required as an input for glycolysis to operate; it must be continuously regenerated from $\text{NADH}$ via respiration or fermentation for glycolysis to keep running.

Anaerobic Respiration

A respiratory pathway found in certain prokaryotes that uses an electron transport chain and oxidative phosphorylation to produce ATP without oxygen, instead utilizing alternative terminal electron acceptors such as nitrate or sulfate.

Aerobic Respiration

A cellular respiration pathway that utilizes an electron transport chain and oxidative phosphorylation to generate ATP, with oxygen ($\text{O}_2$) acting as the final or terminal electron acceptor.

Terminal Electron Acceptor

The final electron-receiving molecule in an energy pathway, such as $\text{O}_2$ in aerobic respiration, inorganic molecules like nitrate or sulfate in anaerobic respiration, or an organic carbon molecule in fermentation.

Substrate-Level Phosphorylation

The direct enzymatic synthesis of ATP by transferring a phosphate group to ADP from an intermediate substrate, which accounts for the net $2\text{ ATP}$ generated during glycolysis.

Oxidative Phosphorylation

The production of ATP driven by the transfer of electrons through an electron transport chain to create a proton gradient that powers ATP synthase.

Pyruvate Oxidation

The metabolic process that converts pyruvate into acetyl-CoA, $\text{CO}_2$, and $\text{NADH}$, located in the mitochondrial matrix in eukaryotes and the cytoplasm in prokaryotes.

Citric Acid Cycle (Krebs Cycle)

A metabolic pathway located in the mitochondrial matrix of eukaryotes and cytoplasm of prokaryotes that consumes acetyl-CoA, $\text{NAD}^+$, and $\text{FAD}$ to generate $\text{CO}_2$, $\text{NADH}$, $\text{FADH}_2$, and ATP/GTP.

Electron Transport Chain (ETC)

A series of membrane-bound complexes located on the inner mitochondrial membrane in eukaryotes and the plasma membrane in prokaryotes that transfer electrons, pump protons to establish a gradient, and indirectly power ATP synthesis.

Endosymbiotic Theory

The evolutionary theory stating that mitochondria originated from an ancestral aerobic bacterium engulfed by an ancestral host cell, explaining why the inner mitochondrial membrane houses the ETC and ATP synthase while the matrix houses pyruvate oxidation and the citric acid cycle.

Warburg Effect

The phenomenon where many cancer cells rely heavily on glycolysis and lactic acid fermentation to meet their energy demands even in the presence of adequate oxygen, potentially aiding biosynthesis, glucose competition, and tumor environment alteration.

Pyruvate Dehydrogenase Complex

A nuclear-encoded multi-enzyme complex located in the mitochondrial matrix that carries out pyruvate oxidation; genetic defects in this complex result in pyruvate and lactic acid accumulation.

Lactate Acidosis

A pathological state characterized by the harmful accumulation of lactic acid and pyruvate in the bloodstream, leading to symptoms including hyperventilation, muscle pain, weakness, abdominal pain, and nausea.

Ketogenic Diet

A therapeutic high-fat, adequate-protein, low-carbohydrate diet that supplies ketone bodies through fatty acid oxidation, bypassing pyruvate dehydrogenase deficiency to produce acetyl-CoA without exacerbating lactate acidosis.

Fatty Acid Oxidation (Oxidative Pathways)

The metabolic process of cleaving fatty acid chains $2$ carbons at a time into acetyl-CoA, which can only enter the oxidative pathways when cells are respiring (aerobically or anaerobically) so that electron carriers can be recycled.