Respiration, Chemiosmosis, and Oxidative Phosphorylation

Vocabulary practice flashcards covering cellular respiration, electron transport chains, chemiosmosis, redox metabolism, nutritional classifications, and mitochondrial uncoupling.

Chemoheterotroph

An organism that obtains its chemical energy from organic molecules and obtains its carbon from pre-existing organic molecules synthesized by other organisms.

Chemoautotroph

An organism that obtains chemical energy from inorganic molecules and synthesizes its own organic molecules by fixing inorganic carbon ($CO_2$).

Photoheterotroph

An organism that uses light as an energy source to drive biochemical reactions but must obtain its carbon from pre-existing organic molecules from biological sources.

Photoautotroph

An organism that uses sunlight as its energy source and fixes inorganic carbon ($CO_2$) to synthesize its own organic molecules.

Substrate-Level Phosphorylation

A mechanism of ATP synthesis where a phosphate group is directly transferred from a high-energy phosphorylated organic molecule to $ADP$, occurring during glycolysis and the citric acid cycle.

Oxidative Phosphorylation

A process that produces the bulk of ATP during cellular respiration by using the electron transport chain to establish a proton gradient, which powers ATP synthase to add inorganic phosphate ($P_i$) to $ADP$.

Oxidation

The loss of one or more electrons by a molecule or atom in a chemical reaction (often accompanied by dehydrogenation in cellular respiration).

Reduction

The gain of one or more electrons by a molecule or atom in a chemical reaction (often accompanied by hydrogenation in cellular respiration).

Redox Reaction

A coupled chemical reaction involving the transfer of electrons from an electron donor (which becomes oxidized) to an electron acceptor (which becomes reduced).

$$NAD^+$$

The oxidized, electron-deficient form of the primary electron shuttle in cells; it acts as an available carrier that accepts two electrons and a proton from food molecules to form $NADH$.

$$NADH$$

The reduced, loaded electron carrier that transports high-energy electrons harvested from food to the electron transport chain, regenerating $NAD^+$ upon donating them.

Electron Transport Chain (ETC)

A series of membrane-embedded protein complexes that accepts electrons from electron carriers like $NADH$ and $FADH_2$, passes them down a redox gradient, and uses the released free energy to pump protons ($H^+$) across the membrane.

Proton-Motive Force

The stored electrochemical potential energy across a biological membrane generated by both a concentration difference ($\text{pH}$ gradient) and an electrical charge difference of protons ($H^+$).

Chemiosmosis

The movement of protons ($H^+$) across a semi-permeable membrane down their electrochemical gradient to drive cellular work, specifically powering the rotational mechanism of ATP synthase.

ATP Synthase

A molecular machine composed of a membrane-spanning rotor base ($F_o$ unit) and a catalytic head knob ($F_1$ unit) that rotates as protons pass through, altering its shape to catalyze $ADP + P_i \rightarrow ATP$.

Aerobic Respiration

A metabolic pathway that uses molecular oxygen ($O_2$) as the terminal electron acceptor, yielding water ($H_2O$) and producing the maximum yield of ATP due to oxygen's high reduction potential ($\text{820 mV}$, with $\text{O}_2$ reduction yielding $\text{-479 kJ mol}^{-1}$).

Anaerobic Respiration

A cellular respiration process that functions in anoxic conditions by utilizing a terminal electron acceptor other than oxygen (such as $NO_3^-$, $SO_4^{2-}$, or $Mn^{4+}$), producing less ATP than aerobic respiration.

Terminal Electron Acceptor

The final compound in the electron transport chain that receives electrons and is reduced; oxygen has the greatest reduction potential, followed by nitrate ($NO_3^-$), manganese ($MnO_2$), ferric iron ($Fe(OH)_3$), and sulfate ($SO_4^{2-}$).

Oxygenic Photosynthesis

A form of photosynthesis evolved by cyanobacteria that releases molecular oxygen ($O_2$) into the environment, historically driving the evolution of oxygen-utilizing electron transport chains and aerobic bacteria.

Bacteriorhodopsin

A light-driven proton pump containing retinal pigment found in prokaryotic Archaea that deprotonates water and pumps protons across the membrane to drive ATP synthesis without using electron transport or redox reactions.

Brown Adipose Tissue (Brown Fat)

A specialized tissue in newborn mammals containing high numbers of mitochondria, small lipid droplets, and extensive vascularization that mediates non-shivering thermogenesis to produce heat.

White Adipose Tissue (White Fat)

An ordinary adult mammalian storage tissue composed of cells containing large lipid droplets, little cytoplasm, few mitochondria, and low oxygen consumption.

Uncoupling Protein 1 (UCP1)

A mitochondrial inner membrane protein in brown fat and thermogenic plants that allows protons to leak back into the matrix, collapsing the proton gradient and dissipating ETC energy as heat instead of generating ATP.

Dinitrophenol (DNP)

A toxic, lipid-soluble chemical uncoupler that carries protons across the inner mitochondrial membrane in all mitochondria, causing a hyper-metabolic state characterized by hyperthermia, rapid breathing, and depleted ATP production.