Practice question

Mitochondrial ancestry traces to engulfment of facultatively aerobic alphaproteobacterium capable of oxidative phosphorylation, possessing electron transport chain, tricarboxylic acid cycle, and beta-oxidation enzymes. Relationship to contemporary Rickettsiales inferred from phylogenetic analyses of cytochrome oxidase, citrate synthase, and small subunit rRNA genes clustering mitochondria with intracellular parasitic alphaproteobacteria. Host likely was Asgard-like archaeon adapted to syntrophy. Endosymbiotic gene transfer relocated majority of alphaproteobacterial genes to host nucleus evolving import apparatus. Energy yield from efficient aerobic respiration facilitated genome expansion, intracellular compartmentalisation, and emergence of complex eukaryotic traits absent in prokaryotes.