Protein biosynthesis can be broken down into two major phases, transcription and translation. Transcription is the first part. The DNA in the nucleus unwinds and a portion of the double helix separates. Messenger RNA then comes into the nucleus and forms a complementary strand to a particular section of the DNA according the sequence of nucleotide bases. Once the messenger RNA strand is formed and leaves the nucleus, the second part (translation) takes place. The messenge RNA travels to a ribosome and the nucleotide sequence is used to sequence together amino acids into a polypeptide. A group of three nucleotides is called a codon and each codon codes for a particular amino acid. The polypeptide that is formed is then folded to give a completed protein. So, in essence, the DNA is converted to RNA which is then converted to a particular sequence of amino acids which ends up being a protein.