Biological Oxidation and Respiratory Chain Practice Flashcards

Comprehensive vocabulary flashcards covering the components of the mitochondrial respiratory chain, ATP synthase structure, inhibitory substances, uncoupling mechanisms, and cellular defense against reactive oxygen species.

Respiratory chain

A complex organized system located in the inner mitochondrial membrane that collects reducing equivalents, transports them to $O_2$, and accumulates energy produced during oxidation to produce ATP.

Inner mitochondrial membrane

A membrane that is 75% protein by weight, loaded with respiratory chain enzymes and ATP synthase, and is impermeable to most organic molecules and ions.

Outer mitochondrial membrane

A membrane usually containing >50% lipid and porins, which permit the diffusion of molecules up to ~10 kDa in size.

Cristae

Folds of the inner mitochondrial membrane that increase the surface area for the incorporation of respiratory enzymes.

Mitochondrial genome

A maternally inherited, circular, double-stranded DNA containing 37 genes, including 13 that encode subunits of respiratory proteins.

Complex I (NADH-CoQ reductase)

An 850 kD complex with 45 subunits and FMN as a prosthetic group; it transports 2 electrons from NADH to CoQ and pumps 4 protons into the intermembrane space.

Complex II (Succinate-CoQ reductase)

A complex consisting of succinate dehydrogenase with FAD, Fe-S clusters, and cytochrome $b_{560}$; it transports electrons from succinate to CoQ but does not pump protons.

CoQ (Ubiquinone)

A mobile component of the respiratory chain that acts as a collector of electrons.

Complex III (CoQ-cytochrome c reductase)

A dimer where each monomer contains 11 subunits (including cytochromes $b_{562}$, $b_{566}$, and $c_1$); it transports electrons from $CoQH_2$ to cytochrome c and pumps 4 protons via the Q-cycle.

Cytochrome c

A low molecular weight peripheral membrane protein that carries electrons from Complex III to Complex IV; it also plays a role in apoptosis by activating caspase.

Complex IV (Cytochrome oxidase)

A dimer containing 13 subunits and 4 redox centers ($Cu_B$, Cytochrome a, Cytochrome $a_3$, and $Cu_A$-center) that reduces $O_2$ to $2H_2O$ and pumps 2 protons per 2 electrons.

Chemiosmotic hypothesis

The theory that the free energy released during the reduction of NADH and $FADH_2$ is used to create a transmembrane electrochemical gradient of protons to drive ATP synthesis.

ATP synthase (Complex V)

A protein complex consisting of $F_1$ (matrix side) and $F_o$ (membrane-embedded) components that synthesizes ATP using the energy from proton flow.

Boyer’s binding change mechanism

A mechanism describing how rotational catalysis in ATP synthase leads to spontaneous ATP formation at catalytic sites on the $\beta$ subunits.

Respiratory control

The regulation of the rate of electron transport in the respiratory chain by the ATP/ADP ratio, reflecting the cell's energy needs.

Oligomycin

An inhibitor of oxidative phosphorylation that specifically inhibits ATP synthase.

Rotenone

An inhibitor of electron transport that acts on Complex I.

Antimycin A

An inhibitor of electron transport that acts on Complex III.

Cyanide ($CN^-$)

A potent inhibitor that blocks the electron transport chain at Complex IV.

Thermogenin

A special uncoupling protein found in brown adipose tissue that allows protons to bypass ATP synthase to generate heat instead of ATP.

CYP enzymes (Cytochromes P450)

Major enzymes in the endoplasmic reticulum involved in drug metabolism and hydroxylation, accounting for about 75% of metabolic reactions.

Glutathione (GSH)

A tripeptide antioxidant that, along with glutathione peroxidase and selenium, detoxifies hydrogen peroxide ($H_2O_2$) into water.

Leber optic atrophy (LHON)

A condition associated with mutations in Complex I (NADH dehydrogenase) of the mitochondrial respiratory chain.

Superoxide ($O_2^{\bullet-}$)

A reactive oxygen species byproduct produced at several sites in the electron transport chain, including Complex I and the Q-cycle of Complex III.