Practice question

Mitochondria originated when an ancestral proto-eukaryote related to Asgard archaea engulfed an aerobic facultative alphaproteobacterium closely related to Rickettsiales order capable of oxidative phosphorylation. Endosymbiont lost majority of genome through endosymbiotic gene transfer to host nucleus and evolved mitochondrial import machinery TOM TIM. Evidence includes double membrane envelope, circular genome resembling alphaproteobacterial chromosome, presence of 70S ribosomes, and phylogenetic clustering of mitochondrial genes with alphaproteobacteria. This single acquisition provided efficient ATP generation driving eukaryotic complexity, distinct from chloroplast cyanobacterial origin.