Genetic Code

DNA must code for the 20 different amino acids found in all organisms.
The information-carrying capabilities of DNA reside in
the sequence of nitrogenous bases. The genetic code is a sequence
of three bases—a triplet code. Genetic code
as reflected in the mRNA that will be produced from DNA. Each
three-base combination is a codon. More than one codon can
specify the same amino acid because there are 64 possible codons,
but only 20 amino acids. This characteristic of the code is referred
to as degeneracy. Note that not all codons code for an amino
acid. The base sequences UAA, UAG, and UGA are all stop
signals that indicate where polypeptide synthesis should end.
The base sequence AUG codes for the amino acid methionine,
which is a start signal.