ATP synthase rows / ATP leavingO₂ arrivingmtDNA nucleoidsCristae (inner membrane folds)A mitochondrion 0.5 µm wide and 1.5 µm long (ruler: 1 tick = 50 nm), cut along its length with the top half removed. The cut edge shows both membranes: the smooth outer one and, about 20 nm inside it, the inner membrane, folded into lamellar cristae that multiply its area several times. The respiratory chain in those folds pumps protons out of the matrix; ATP synthases, lined up in rows along the sharp crista edges, let them back in and make ATP, about 2.5 per oxygen atom. With no ADP the membrane potential sits near 180 mV and oxygen use idles; give it ADP and oxygen use rises 5–8×, the potential sags to about 150 mV and ATP streams out. Particles are not to scale, and their flow shows relative rates, not real time.
0.5 × 1–2 µm典型尺寸typical size~150–180 mV内膜电位 Δψinner-membrane potential Δψ~2.5 ATP / ONADH 的 P/O 比P/O ratio for NADH5–8×加 ADP 后耗氧上升（state 3 / state 4）O₂ uptake rise with ADP (state 3 / state 4)16,569 bp人类 mtDNA，37 个基因human mtDNA, 37 genes100s–1000s每个细胞的线粒体数mitochondria per cell