Cells make their largest decisions at a few regulatory hubs: AMPK, which senses energy; mTOR, which decides whether to grow; p53, which guards the genome; and NF-κB, which coordinates inflammation and immunity. These hubs regulate one another in a web rather than a chain of command, but they have something in common. AMPK reads the ratio of AMP and ADP to ATP directly. mTOR checks the supply of S-adenosylmethionine through a dedicated sensor. p53 carries acetyl, methyl, ubiqu