GENETICS

The Genetic Code

1961 to 1966 CE

Phanerozoic · Cenozoic · Quaternary · Holocene · Meghalayan

Three bases spell one amino acid, and the dictionary is very nearly the same in every living thing. It was cracked by feeding synthetic RNA to cell extracts and seeing what came out: a strand of pure uracil produced a protein of pure phenylalanine, and that was the first word. The other sixty-three took five more years.

Why it matters

A shared dictionary is the single strongest piece of evidence that everything alive descends from one population of cells. The assignments are arbitrary, in the sense that no chemistry requires those three letters to mean that amino acid, so finding the same arbitrary choices in a bacterium and in a human means inheritance rather than coincidence.

Dating & uncertainty

A synthetic RNA of pure uracil produced a protein of pure phenylalanine in 1961, which gave the first word. The remaining sixty-three took five more years.

Sources

1. Nirenberg & Matthaei (1961), PNAS · The dependence of cell-free protein synthesis in E. coli upon naturally occurring or synthetic polyribonucleotides
2. Crick et al. (1961), Nature · General nature of the genetic code for proteins
3. Nirenberg (2004), Trends in Biochemical Sciences · Deciphering the genetic code: a personal account

Earth history as one day

23:59:59.99881.2 ms before midnight

if Earth’s 4.54 billion years were compressed into a single day