The sequence of nucleotides in DNA in can be read only by first separating the DNA double helix (performed by the enzyme helicase). The information is “read” by RNA polymerase, which then transcribes a corresponding piece of RNA. If the purpose of the RNA is to encode a protein, it can then be read by a structure called a ribosome, which creates proteins according to the specific ordering of the nucleotides in the RNA strand.

The ordering of the nucleotides in DNA (and thus the nucleosides in RNA) is extremely important in determining the function of a protein. Nucleotides are read in groups of three. These groups of three are called codons, and each codon tells the ribosome to incorporate a specific amino acid into the peptide/protein it creates. There are also specific codons that tell the ribosome to start or stop creating a peptide. Any mistake in the copying of DNA or RNA can potentially lead to major problems, so it’s important that the cellular machinery that carries out these processes is extremely accurate.