PNA is the name of the genetic molecule used on Pern. Unlike Earth DNA, it has only 3 bases, A, B, and C, arranged in triads as with DNA, producing only 27 combinations. PNA is triple-stranded. There is a main strand and two secondary strands. In addition to the three bases there are four extra molecules, A', B', C', and N used on the secondary strands. Only the primary strand is used for synthesizing proteins. On the secondary strands, A' bonds with A, B' with B, and C' with C. N bonds with all three bases. The secondary strands alternate A'/B'/C' with N, in turn alternating with each other. Thus, if the primary strand has a sequence ACABCA, the first secondary strand will have A'NA'NC'N while the second strand will have NC'NB'NA'.