The chemical structure of a single strand of DNA gives little insight into its biological function as a carrier of genetic information. The oligonucleotides GCAT and TACG are distinct molecules with different chemical and biophysical properties. By convention, the prefixes 5'- and 3'- are not written, and nucleic acid sequences are written in the 5' to 3' direction. The tetranucleotide in Figure 8a has the sequence 5'-GCAT-3' and the tetranucleotide in Figure 8b has the sequence 5'-TACG-3'. The nucleic acid chain therefore has directionality.
One end of a nucleic acid strand has a 5'-hydroxyl group (primary hydroxyl) and the other end has a 3'-hydroxyl group (secondary hydroxyl). Chemical structures of the oligonucleotides dGCAT (left) and dTACG (right)
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