Cellular Respiration: Harvesting Chemical Energy

Vocabulary practice flashcards covering the key terms, mechanisms, stages, and regulatory enzymes of cellular respiration and fermentation.

Catabolic Pathways

Metabolic pathways that release energy by breaking down complex organic molecules into simpler compounds in an exergonic process.

Fermentation

A catabolic process resulting in the partial degradation of sugars that occurs without oxygen (anaerobic).

Cellular Respiration

An aerobic catabolic process that consumes oxygen and organic molecules to break down fuels and yield ATP.

Oxidation

The loss of electrons from one substance during a redox reaction.

Reduction

The addition of electrons to a substance during a redox reaction, reducing its amount of positive charge.

Reducing Agent

The electron donor in an oxidation-reduction (redox) reaction.

Oxidizing Agent

The electron acceptor or receptor in an oxidation-reduction (redox) reaction.

$$\text{NAD}^+$$

A coenzyme that functions as an electron acceptor and oxidizing agent during cellular respiration.

NADH

The reduced form of $\text{NAD}^+$ that holds stored energy tapped to synthesize ATP.

Electron Transport Chain

A sequence of electron carrier proteins located in the cristae of the mitochondrion that shuttle electrons down a series of steps to $O_2$, releasing energy in manageable amounts.

Glycolysis

A ten-step metabolic pathway occurring in the cytoplasm that splits glucose into two molecules of pyruvate, consisting of an energy investment phase and an energy payoff phase.

Substrate-Level Phosphorylation

The direct enzymatic transfer of a phosphate group from an organic substrate molecule to ADP to form ATP, occurring during glycolysis and the citric acid cycle.

Oxidative Phosphorylation

The production of ATP using energy derived from the redox reactions of the electron transport chain and chemiosmosis, accounting for almost $90\%$ of ATP generated in cellular respiration.

Acetyl CoA

Acetyl coenzyme A; the sulfur-containing compound formed from pyruvate that enters the citric acid cycle to link it with glycolysis.

Citric Acid Cycle

An eight-step metabolic cycle in the mitochondrial matrix that completes the breakdown of glucose by oxidizing acetyl CoA to $CO_2$, generating $1\,\text{ATP}$, $3\,\text{NADH}$, and $1\,\text{FADH}_2$ per turn.

Chemiosmosis

An energy-coupling mechanism that uses the energy stored in a hydrogen ion ($H^+$) gradient across a membrane to drive cellular work, specifically ATP synthesis.

ATP Synthase

A complex of membrane proteins featuring a rotor, stator, rod, and catalytic knob that uses the exergonic flow of $H^+$ to drive the phosphorylation of ADP to ATP.

Proton-Motive Force

The potential energy stored in an $H^+$ gradient across a membrane, emphasizing its capacity to perform cellular work.

Alcohol Fermentation

A type of anaerobic catabolism where glycolysis is followed by the conversion of pyruvate into ethanol in two steps, releasing $CO_2$ and regenerating $\text{NAD}^+$.

Lactic Acid Fermentation

A type of anaerobic catabolism where pyruvate is reduced directly by NADH to form lactate as an end product with no release of $CO_2$, regenerating $\text{NAD}^+$.

Facultative Anaerobes

Organisms, such as yeasts and many bacteria, that can survive using either fermentation or cellular respiration depending on oxygen availability.

Phosphofructokinase

An allosteric enzyme in glycolysis that acts as a pacemaker for respiration, inhibited by ATP and citrate and stimulated by AMP.