Page "Protein primary structure" Paragraph 61

Any linear-chain heteropolymer can be said to have a " primary structure " by analogy to the usage of the term for proteins, but this usage is rare compared to the extremely common usage in reference to proteins.

In RNA, which also has extensive secondary structure, the linear chain of bases is generally just referred to as the " sequence " as it is in DNA ( which usually forms a linear double helix with little secondary structure ).

Other biological polymers such as polysaccharides can also be considered to have a primary structure, although the usage is not standard.