Unit 3 – Electron Transport Chain and Oxidative Phosphorylation (VOCABULARY Flashcards)

A vocabulary set covering the structure of mitochondria, the electron transport chain (Complexes I–IV), ATP synthase (Complex V), energy yield (P/O), regulation, uncoupling, ROS/antioxidants, and clinical links such as hypoxia and cyanide poisoning; designed to reinforce key terms and definitions from the lecture notes.

Mitochondrion

Double-m membrane-bound organelle where aerobic metabolism occurs; contains intermembrane space and matrix; cristae increase surface area for ETC/ATP synthesis.

Cristae

Invaginations of the inner mitochondrial membrane forming microcompartments that increase surface area and influence proton gradients.

Porins

Proteins in the outer mitochondrial membrane that permit diffusion of small molecules into the intermembrane space.

Inner mitochondrial membrane

Membrane rich in proteins (~75% by mass) that is impermeable to most ions/metabolites and houses the ETC and ATP synthase.

NADH and FADH2

Electron carriers produced in glycolysis, PDH, and TCA that donate electrons to the ETC.

Glycerol-3-phosphate shuttle

Cytosolic NADH electrons are transferred to dihydroxyacetone phosphate to form glycerol-3-phosphate, which is reoxidized by a mitochondrial FAD-dependent enzyme to FADH2; delivers electrons to the ETC (Complex II entry) mainly in muscle/nerve.

Malate–aspartate shuttle

NADH from cytosol is transferred as malate into the matrix and reoxidized to oxaloacetate, yielding matrix NADH; heart cells preferentially use this shuttle.

Adenine nucleotide translocase (ADP–ATP translocator)

Inner membrane transporter that exchanges ATP (out) for ADP (in) across the IMM, driving ATP export and ADP import.

Phosphate (Pi) transporter

Electroneutral Pi–H+ symport that imports inorganic phosphate into the mitochondrial matrix for ATP synthesis.

Coenzyme Q (CoQ, ubiquinone)

Lipid-soluble electron carrier in the inner membrane; accepts electrons from Complexes I/II and transfers them to Complex III as CoQH2.

Complex I (NADH:CoQ oxidoreductase)

Largest ETC complex; contains FMN and Fe–S centers; oxidizes NADH and reduces CoQ; pumps protons across the IMM.

FMN (flavin mononucleotide)

Redox cofactor in Complex I that accepts/donates two electrons during NADH oxidation.

Iron–sulfur clusters (Fe–S)

Redox centers in Complex I (and other complexes) that shuttle electrons via Fe3+/Fe2+ transitions.

Complex II (succinate dehydrogenase)

TCA enzyme that transfers electrons from succinate (via FADH2) to CoQ; does not pump protons under normal operation.

Complex III (CoQ–cytochrome c oxidoreductase, bc1 complex)

Transfers electrons from CoQH2 to cytochrome c; contains Rieske [2Fe–2S] center; operates via the Q cycle to pump protons.

Rieske center

[2Fe–2S] iron–sulfur cluster in Complex III essential for electron transfer.

Q cycle

Mechanism in Complex III where two electrons from a single CoQH2 are split: one goes to cytochrome c, the other reduces a second CoQ at Qi site; overall proton pumping occurs.

Cytochrome c

Soluble heme protein in the intermembrane space that shuttles electrons between Complex III and Complex IV.

Complex IV (cytochrome c oxidase)

Catalyzes four-electron reduction of O2 to two H2O; contains CuA/CuB centers and cytochromes a and a3; transmembrane subunits encode by mtDNA.

CuA and CuB centers

Copper redox centers in Complex IV that participate in the multi-electron reduction of O2.

Cytochromes a and a3

Heme-containing redox centers in Complex IV that participate in electron transfer to O2.

ATP synthase (Complex V)

Rotary enzyme (F0–F1) that uses the proton motive force to synthesize ATP from ADP and Pi; F0 forms the membrane rotor; F1 contains catalytic subunits.

F0 and F1 subunits

F0 is membrane-embedded rotor; F1 is peripheral catalytic unit; together couple proton flow to ATP synthesis.

c-ring

Ring of c subunits in F0 that rotates as protons move through the stator; number of subunits varies (8–15) and determines proton-to-ATP ratio.

Binding Change Mechanism (Boyer model)

Three catalytic states (open L, tight T, and empty O) in the F1β3 subunits; proton flow drives conformational changes enabling ATP synthesis/release.

P/O ratio

ATP produced per oxygen atom reduced; typical values: ~2.5 ATP per NADH and ~1.5 ATP per FADH2 under physiological conditions.

Respiratory control (ADP–ATP control)

Regulation of oxidative phosphorylation by cellular energy needs; higher ADP/ATP drives increased respiration and ATP synthesis.

Proton motive force (pmf)

Electrochemical gradient (Δψ and ΔpH) across the inner mitochondrial membrane that powers ATP synthesis.

Uncoupling proteins (UCPs; e.g., UCP1)

Proteins that dissipate the proton gradient to generate heat instead of ATP; UCP1 in brown fat enables non-shivering thermogenesis.

DNP (dinitrophenol)

Protonophore uncoupler that carries protons across membranes, dissipating pmf and uncoupling electron transport from ATP synthesis.

Brown adipose tissue thermogenesis

Heat production via uncoupled respiration; involves UCP1 regulated by norepinephrine/cAMP signaling.

Randle cycle (glucose–fatty acid cycle)

Fatty acid oxidation inhibits glycolysis through citrate-mediated PFK inhibition, favoring fat as fuel in heart and sparing glucose.

Pasteur effect

Presence of O2 decreases glucose consumption by shifting from glycolysis to more efficient aerobic metabolism.

Hypoxia

Low tissue oxygen; reduces ETC activity, shifts to anaerobic glycolysis, increases lactate, and decreases ATP production.

Reactive oxygen species (ROS)

Reactive oxygen-containing chemicals (O2−, H2O2, OH•) produced during metabolism that can damage lipids, proteins, and DNA.

Antioxidant defenses (enzymatic)

SOD, catalase, glutathione peroxidase defend against ROS; convert reactive species to non-toxic forms.

Nonenzymatic antioxidants

Dietary and endogenous molecules (vitamin E, vitamin C, carotenoids, flavonoids, uric acid, melatonin) that scavenge free radicals.

Glutathione system

Glutathione (GSH/GSSG) and enzymes (glutathione peroxidase/reductase) protect against ROS; NADPH from PPP regenerates GSH.

Mitochondrial genome

13 mtDNA-encoded genes (hydrophobic subunits) plus 22 tRNAs and 2 rRNAs; ~16.6 kb circular DNA; maternally inherited.

Mitochondrial protein import

Most mitochondrial proteins are encoded by nuclear genes and imported into mitochondria; mitochondrion retains limited genome.