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

A Handle, Not Just a Fuel Most people know adenosine triphosphate, ATP, as the cell’s fuel. Fewer know that the same adenosine unit sits inside many of the cell’s most vital molecules that carry electrons, methyl groups and acetyl groups, inside the letters of RNA and DNA, inside the signals that cells send one another, and inside the folded architecture of RNA itself. The repeated use of one small molecule for so many unrelated jobs is a clue to the deep history of life and