Levels of Structure in Nucleic Acids
We identified four levels of structure-primary, secondary, tertiary, and quaternary-in proteins. Nucleic acids can be viewed in the same way. The primary structure of nucleic acids is the order of bases in the polynucleotidesequence, and the secondary structure is the three-dimensional conformation of the backbone. The tertiary structure is specifically the supercoiling of the molecule.
There are two principal types of nucleic acids, DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
Important differences between DNA and RNA appear in their secondary and tertiary structures, and so we shall describe these structural features separately for DNA and for RNA. Even though nothing in nucleic acid structure is directly analogous to the quaternary structure of proteins, the interaction of nucleic acids with other classes of macromolecules (for example, proteins) to form complexes is similar to the interactions of the subunits in an oligomeric ribosomes (the polypeptide-generating machinery of the cell); another is the self-assembly of tobacco mosaic virus, in which the nucleic acid strand winds through a cylinder of coat-protein subunits.
The two principal kinds of nucleic acids are DNA and RNA.
The primary structure of nucleic acids is the order of bases. The second-ary structure is the three-dimensional conformation of the backbone. The tertiary structure is the supercoiling of the molecule.