Practice question

Mitochondria are multifunctional organelles originating from endosymbiosis retaining sixteen point six kilobase circular genome encoding thirteen oxidative phosphorylation polypeptides, twenty two tRNAs, two rRNAs. Inner membrane cristae house electron transport chain complexes generating proton gradient driving F1Fo ATP synthase producing up to thirty ATP per glucose, contributing most cellular ATP under aerobic conditions. Matrix contains calcium uniporter MCU complex buffering cytosolic spikes shaping NFAT signaling and buffering, also participates in heme pathway where ALA synthase in matrix initiates five-aminolevulinate condensation from succinyl-CoA and glycine, intermediate steps cytosolic, final ferrochelatase inserting Fe2+ into protoporphyrin IX at inner membrane, critical for hemoglobin and cytochromes. Additional functions include Fe-S cluster biogenesis via ISC machinery, amino acid metabolism, thermogenesis via UCP1, apoptosis regulation. Protein folding of secretory pathway requiring disulfide formation oxidative environment occurs in ER lumen assisted by BiP PDI calnexin, not mitochondria, whose matrix is reducing containing Hsp60 Hsp10 chaperonin for imported proteins but not bulk folding of cytosolic cohort. Therefore protein folding excluded.