Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein-coding genes such as transfer RNA or small nuclear RNA genes, the product is a functional RNA. Gene expression is a tightly regulated process that allows a cell to respond to its changing environment.It acts as both an on/off switch to control when proteins are made and also a volume control that increases or decreases the amount of proteins made. There are two key steps involved in making a protein, transcription and translation.

Transcription is when the DNA in a gene? is copied to produce an RNA? transcript called messenger RNA? (mRNA).This is carried out by an enzyme? called RNA polymerase which uses available bases from the nucleus? of the cell to form the mRNA. RNA is a chemical similar in structure and properties to DNA, but it only has a single strand of bases? and instead of the base thymine ?(T), RNA has a base called uracil. Translation occurs after the messenger RNA (mRNA) has carried the transcribed ‘message’ from the DNA to protein-making factories in the cell, called ribosomes.The message carried by the mRNA is read by a carrier molecule called transfer RNA ?(tRNA).The mRNA is read three letters (a codon) at a time.Each codon specifies a particular amino acid?. For example, the three bases ‘GGU’ code for an amino acid called glycine.As there are only 20 amino acids but 64 potential combinations of codon, more than one codon can code for the same amino acid.