For each gene, one DNA strand functions as a template for transcription to produce mRNA.

The base-pairing rules for DNA synthesis also guide transcription, but uracil (U) takes the place of thymine (T) in RNA.

In translation, the mRNA is read in the 5' - 3' direction as a sequence of base triplets, or codons.

Each codon specifies an amino acid to be added to the growing polypeptide chain.