Roughly two metres of DNA has to coil into a nucleus about 6 micrometres across, and the nucleus is only one of dozens of organelles running at once. ATP output is always pinned by whatever is scarcest: without glucose the cell runs out of fuel, without oxygen it has fuel it cannot burn. Under starvation, autophagy switches on and lysosomes digest worn-out organelles to buy time, while inside a mitochondrion the folded cristae carry the electron transport chain.
Roughly two metres of DNA has to coil into a nucleus about 6 micrometres across, and the nucleus is only one of dozens of organelles running at once. ATP output is always pinned by whatever is scarcest: without glucose the cell runs out of fuel, without oxygen it has fuel it cannot burn. Under starvation, autophagy switches on and lysosomes digest worn-out organelles to buy time, while inside a mitochondrion the folded cristae carry the electron transport chain.
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