Genomes: not just genes

Regulating protein production

Although we carry complete copies of our genome in most of our cells, only certain genes are switched on at any one time. Control sequences in the DNA contain the instructions to switch genes on and off and to produce varying amounts of different proteins at different times.

In humans and other complex organisms, the coding sequences of the genes are separated into small chunks by lengths of noncoding DNA. The coding sequences are called exons, and the noncoding areas between them are called introns. Once the DNA is transcribed into RNA, these noncoding sequences are usually cut or 'spliced out'.

However, the presence of these noncoding gene sequences is thought to give the cell the ability to generate many proteins from one gene. This way, the protein could be derived from all the exons, use only some of them, or perhaps even use some of the usually noncoding sequences to make different proteins. This is known as 'alternative splicing'.