DNA is used to code proteins. This requires two steps: transcription and translation.Transcription is the conversion of double stranded DNA into a single stranded mRNA molecule. DNA nucleotides bind to their complementary RNA nucleotides eg Cytosine binds Guanine and RNA polymerase completes the RNA molecule.The mRNA then is processed and migrates to the cytoplasm where translation occurs. In translation the nucleotides are read in triplets (the triplet code) by ribosomes to code amino acids. Additionally, some triplets encode ‘start’ or ‘stop’ codons which signal where translation of an mRNA molecule is to begin and end respectively.