Chapter 9: Cellular Respiration

Comprehensive vocabulary flashcards covering the biochemical pathways, key terms, cellular structures, and energetic mechanisms of Chapter 9: Cellular Respiration.

Mechanical Work

A form of cellular work involving motor proteins and muscle contraction powered by the phosphorylation of motor proteins by ATP.

Transport Work

Cellular work that involves moving solutes across a membrane against a concentration gradient by having ATP phosphorylate transport proteins.

Chemical Work

Cellular work that drives endergonic, anabolic reactions and builds complex biological molecules by having ATP phosphorylate key reactants.

1st Law of Thermodynamics

The thermodynamic principle stating that energy cannot be created or destroyed; it can only be transformed from one form to another.

Aerobic Respiration

The most common and efficient catabolic pathway, which requires oxygen ($O_2$) and organic fuel to produce carbon dioxide, water, and ATP via the overall reaction: $C_6H_{12}O_6 + 6\,O_2 \rightarrow 6\,CO_2 + 6\,H_2O + \text{Energy}$.

Oxidation

The loss of electrons from a substance during a redox reaction, represented by the electron donor (reducing agent) such as glucose during cellular respiration.

Reduction

The addition or gain of electrons by a substance during a redox reaction, represented by the electron acceptor (oxidizing agent) such as oxygen during cellular respiration.

$NAD^+$ / $NADH$

A primary coenzyme and electron carrier that captures high-energy electrons released from oxidized fuel molecules, losing very little potential energy and shuttling electrons to the electron transport chain.

Substrate-Level Phosphorylation

A mode of ATP synthesis where an enzyme directly transfers a phosphate group from an organic substrate molecule to ADP, 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, generating approximately $90\%$ of cellular respiration's ATP.

Glycolysis

A ten-step metabolic pathway located in the cytosol that splits one 6-carbon glucose into two 3-carbon pyruvate molecules without requiring oxygen, yielding a net gain of $2\text{ ATP}$ and $2\text{ NADH}$.

Pyruvate Oxidation

The intermediate stage occurring upon pyruvate entry into the mitochondrion, where a transport protein facilitates its conversion into acetyl CoA, releasing $CO_2$ and producing $NADH + H^+$.

Citric Acid Cycle

A metabolic cycle in the mitochondrial matrix that oxidizes acetyl CoA derivatives, yielding $2\text{ ATP}$, $8\text{ NADH} + 8\text{ H}^+$, $2\text{ FADH}_2$, and $6\text{ CO}_2$ per initial glucose molecule (including the intermediate step).

Cristae

Infoldings of the inner mitochondrial membrane that provide extensive surface area to accommodate numerous electron transport chain complexes and ATP synthases.

Cytochromes

Iron-containing proteins embedded within the inner mitochondrial membrane that form the electron transport chain, sequentially increasing in electronegativity downhill toward oxygen.

Chemiosmosis

The energy-coupling mechanism that utilizes energy stored in a hydrogen-ion ($H^+$) gradient across a membrane to drive the synthesis of ATP.

Proton-Motive Force

The capacity of the high-concentration $H^+$ gradient established across the inner mitochondrial membrane to perform work as protons flow back through facilitated diffusion.

ATP Synthase

A multiprotein rotary complex spanning the inner membrane that harnesses the downhill flow of protons from the intermembrane space to the matrix to phosphorylate ADP into ATP.

Obligate Aerobes

Organisms that strictly require oxygen to survive and cannot produce sufficient energy without aerobic cellular respiration.

Obligate Anaerobes

Organisms that cannot live in the presence of oxygen and rely entirely on anaerobic respiration or fermentation for survival.

Facultative Anaerobes

Organisms that can generate ATP by either fermentation or aerobic respiration, preferentially utilizing aerobic respiration when oxygen is available.

Anaerobic Respiration

A catabolic pathway used by prokaryotes in anoxic environments where an inorganic substance other than $O_2$, such as sulfate ($SO_4^{2-}$) or nitrate ($NO_3^-$), serves as the terminal electron acceptor, yielding between $2$ and $28\text{ ATP}$.

Alcohol Fermentation

An anaerobic catabolic pathway in yeast and bacteria in which pyruvate is converted to ethanol, releasing $CO_2$ and regenerating $NAD^+$ to yield roughly $2\text{ ATP}$ per glucose.

Lactic Acid Fermentation

An anaerobic catabolic pathway in which pyruvate is directly converted to lactate without the release of $CO_2$, regenerating $NAD^+$ to sustain glycolysis.

Respiratory Membrane

Infolded plasma membranes in aerobic prokaryotes that harbor electron transport chains and ATP synthases to perform cellular respiration in the absence of mitochondria.