Mitochondria: Structure, Import, and Oxidative Phosphorylation

Vocabulary flashcards covering mitochondrial structure, genetic material, import mechanisms, and the basics of oxidative phosphorylation and ATP production as described in the notes.

Mitochondria

Double-membraned organelles (~1700 per cell; ~22% of cell volume) with Outer Membrane, Intermembrane Space, Inner Membrane, and Mitochondrial Matrix; site of the electron transport chain (ETC) and oxidative phosphorylation.

Outer membrane porins

Channels in the outer membrane that permit entry of molecules smaller than ~5 kDa and participate in mitochondrial lipid synthesis.

Intermembrane Space (IMS)

Space between the outer and inner membranes; small molecules have cytosol-like concentrations, but protein composition differs (e.g., cytochrome C resides here).

Inner Membrane (IM)

Convoluted membrane with large surface area housing the ETC, ATP synthase, and transporters for ATP.

Mitochondrial Matrix (MM)

Fluid inside the inner membrane containing TCA cycle enzymes, beta-oxidation enzymes, mitochondrial DNA, ribosomes, tRNAs, and gene-expression/DNA repair machinery.

Cytochrome C

Electron carrier in the ETC located in the IMS; can associate with the inner membrane via cardiolipin and is released into the cytosol during apoptosis.

Cardiolipin

Phospholipid (~20% of the inner membrane) that helps anchor cytochrome c and supports ETC function.

Mitochondrial DNA (mtDNA)

Small circular genome (~16.5 kb) with 37 genes (13 membrane proteins, 22 tRNAs, 2 rRNAs); essential for mitochondrial function.

MTS/MLS (mitochondrial targeting signal / mitochondrial localization signal)

N-terminal amphipathic helix with alternating hydrophobic and positively charged residues that targets proteins to mitochondria and is cleaved after import.

Chaperone proteins

Proteins that assist in refolding mitochondrial proteins after import.

Protein import requirements (Arg/Lys)

Import into mitochondria requires positively charged residues (arginine and lysine) and many hydrophobic amino acids.

Amphipathic helix

Structural feature of MTS: alternating hydrophobic and positively charged amino acids that form a helix.

Endosymbiotic origin

Mitochondria evolved from aerobic bacteria engulfed by an archaeal-derived eukaryotic cell, forming a symbiotic relationship.

NADH

Electron donor to the ETC; produced in the TCA cycle and by other catabolic processes; its oxidation drives ATP production.

FADH2

Electron donor to the ETC at Complex II; yields fewer protons pumped than NADH, contributing to ATP generation.

Proton gradient / proton-motive force

Two components: membrane potential (ΔV) and pH gradient (ΔpH); together drive protons back into the matrix to power ATP synthesis.

Oxygen as terminal electron acceptor

O2 accepts electrons at Complex IV (cytochrome c oxidase) to form water during oxidative phosphorylation.

Complex II (succinate dehydrogenase)

ETC member that transfers electrons from FADH2 to CoQ but does not pump protons.

ATP synthase (F1F0)

Enzyme that synthesizes ATP; F1 head is stationary, F0 rotor rotates; driven by proton flow; can run in reverse hydrolyzing ATP.

Chemiosmotic coupling

Coupling of the proton-motive force to ATP synthesis by ATP synthase.

Stage 1 of oxidative phosphorylation

ETC and proton pumping generate a proton gradient; NADH/FADH2 energy powers electron transfer; O2 is reduced to H2O.

Stage 2 of oxidative phosphorylation

ATP synthesis driven by the proton-motive force across the inner membrane via ATP synthase.

Mitochondrial diseases

Chronic genetic disorders; ~1 in 5,000 individuals; ~15% due to mtDNA mutations; others due to nuclear gene mutations affecting mitochondrial function.

Oxygen-to-water concept in ETC

Electrons are ultimately transferred to O2 at Complex IV to form H2O, closing the ETC.