The year is 1961. Francis Crick's team has just shown that every three bases of DNA specify one amino acid.
The Visitor steps into the cell's archive and finds a library written in four letters, read three letters at a time.
A Four-Letter Language
- Four bases form the alphabet. Words are three bases long, which gives 64 codons for 20 amino acids plus 3 stop signals.
- The page describes the code as redundant. Several codons can name the same amino acid, and a change in the third position of a codon often still names the same amino acid.
- The same 64-codon table serves E. coli, sequoia trees, and human neurons.
- Freeland and Hurst (1998) compared the actual code with one million random codes. The page reports that the actual code ranks in the top 0.0001% for limiting the damage of single-base changes.
The four letters drift while the helix turns. The site page carries the codon table and the parameter explorer.
Why does the page call a three-base word the minimum sufficient length for this alphabet?
Four bases in words of three give 64 words, enough for 20 amino acids plus stop signals. Words of two give 16, which is fewer than 20.
The genetic code is a four-letter language with three-letter words, shared by all living things and arranged to limit the effect of single-letter changes.
The Visitor lights node 01 on the coherence map and sees that it connects to Error Correction.
See the map