DNA in the nucleus codes for the joining of amino acids in a certain order to produce specific proteins.  The sequence of amino acids determines the type of protein that is made.

In RNA uracil is found instead of thymine.

Complementary bases:  A and T (or A and U), C and G

Triplet Code

There are about 20 different amino acids. Three bases are needed to code for an amino acid (triplet code).  These three bases together are known as a codon.  The sequence of bases is always read in one particular direction.

Each amino acid has a different codon:

                                    CAA stands for the amino acid valine

                                    TTT stands for the amino acid lysine

                                    CCC stands for the amino acid leucine

                                    GGC stands for the amino acid glycine

There are also three codes for stopping the formation of an amino acid chain.  These are UAA, UAC, or UGA.

Genes and Genomes

A length of DNA which codes for the whole of one protein is called a gene.  The total set of genes in a cell is called the genome.