Practice question

Double membrane architecture provides compartments for energy transduction and genetic separation. Mitochondria possess outer membrane containing porins VDAC1-3 allowing metabolite exchange up to 5 kDa and TOM complex for importing nuclear-encoded proteins, and inner membrane highly impermeable and folded into cristae via MICOS complex and ATP synthase dimer rows generating curvature, housing electron transport chain Complexes I to IV and ATP synthase utilizing chemiosmotic proton gradient established by proton pumping for ATP synthesis. Intermembrane space accumulates protons. Matrix contains TCA cycle enzymes, mtDNA nucleoids, mitoribosomes. Outer membrane derived evolutionarily from host vesicle, inner from endosymbiont. Golgi apparatus, lysosomes, peroxisomes are single membrane organelles performing processing without chemiosmosis. Chloroplasts also double membrane with thylakoids inside. Nuclear envelope is double membrane with pores. Identification of mitochondria as double membrane organelle underlies understanding of apoptosis regulation via cytochrome c release from intermembrane space through Bax/Bak pores and calcium handling at ER-mitochondria contact sites essential for metabolism.