Python Programming for Biology: Bioinformatics and Beyond

Table  11.1.   A  table  of  the  standard  genetic  code.  Messenger  RNA  molecules  are

translated  into  protein  sequences  at  a  large  molecular  assembly  called  a  ribosome.

This takes subsequent groups of three RNA nucleotides, called codons (starting from

an  ‘AUG’)  and  joins  different  amino  acids  into  a  growing  polypeptide  chain,

---

according to which codon sequence is present. The mapping between the three-letter

RNA codons and each amino acid is known as a genetic code. In most cases multiple

codons  (of  which  there  are  64  in  total)  correspond  to  a  single  amino  acid  (of  which

there are 20 in total). Some of the codons do not correspond to any amino acid and

cause  the  protein  chain  synthesis  to  stop.  The  table  shown  is  the  standard  genetic

code,  which  is  valid  for  the  genes  found  in  the  cell  nucleus  of  most  of  the  most

commonly  studied  organisms.  There  are  small  variations  compared  to  this  code  in