ABSTRACT
The genetic code is the rules that specify how the nucleotide sequence of an mRNA is translated into the amino acid sequence of a polypeptide. The nucleotide sequence is read as triplets called codons. During translation, the sequence of an mRNA molecule is read from its 5' end by ribosomes which then synthesize an appropriate polypeptide. Both in prokaryotes and in eukaryotes, the DNA sequence of a single gene is colinear with the amino acid sequence of the polypeptide it encodes. The genetic code is therefore said to be degenerate. In fact, only methionine and tryptophan are represented by a single codon. As a result of the genetic code's degeneracy, a mutation that changes only a single nucleotide in DNA, and hence changes only a single nucleotide in the corresponding mRNA, often has no effect on the amino acid sequence of the encoded polypeptide.
