Canal-U

2.3. The genetic code

Genes code for proteins. What is the correspondence betweenthe genes, DNA sequences, and the structure of proteins? The correspondence isthe genetic code. Proteins have indeedsequences of amino acids. There are 20 amino acidsin the living world. They can be named by a single letter,3 letters or their full name. It means that a protein can berepresented by a sequence of letters in a 20 letter alphabet. Let's come back again on thiscorrespondence between gene and protein. Genes are regions of DNA. These regions are first transcribedinto RNA and then RNA into proteins. And proteins’ sequences of aminoacids fold into 3D structures. Like here, some helixes. Translation is the process whichgoes from RNA to proteins. What is the code used bythis translation process? The code is the correspondencebetween DNA-RNA sequences, a four letter alphabet, to aminoacids sequences, protein, twenty letter alphabet. So let's think a littlebit about the structure of this code. It cannot be a one to onecorrespondence that is one nucleotide of DNA or RNA to one amino acid.