When a protein is being produced by a cell, the genes are expressing. The genes refer to a specific sequence of nucleotides on the DNA coding for a paricular amino acid. First, the code on the DNA is copied onto an mRNA. This process is called the transcription which is followed by translation. The mRNA is used as a template to synthesize a chain of polypeptide containing amino acids and the process is called translation. Thus, gene expression refers to the process by which the information in the gene of a DNA is expressed as a protein.