Re: codon usage and amino acids

Stephanie:



This works because amino acids do not interact directly with the codons in the 
messenger RNA. It was a problem solved by Francis Crick who recognised that 
amino acids and nucleotides could not interact with each other and suggested 
that there were what he called "adaptor molecules" that broguht amino acids to 
the correct places on the mRNA. At about the same time, Zamecnik, Stephenson and 
Hoagland, working on protein synthesis in vitro, found the molecules - small RNA 
molecules - transfer RNA or tRNA.



A tRNA has a binding site for a particular amino acid and a triplet 
corresponding to the codon for that amino acid. So while methionine has only one 
tRNA, valine has 4 tRNAs corresponding to the four codons for valine.