A DNA molecule consists of two long polynucleotide chains composed of four types of nucleotides subunits. Each of these chains is known as a DNA chain or a DNA strand. DNA is made of four types of nucleotides, which are linked covalently into a polynucleotide chain (a DNA strand) with a sugar-phosphate backbone from which the bases (A, C, G, and T) extend.
The sugar-phosphate form the backbone of DNA helix and is the outside, interconnected by the complementary base pairs like rungs of a ladder.
X-ray diffraction patterns of DNA show that there are approximately 10 bases per turn in DNA. The asymmetrical spacing of the sugar-phosphate backbones generates major grooves (where the backbone is far apart) and minor grooves (where the backbone is close together). Proteins use these grooves to bind to DNA, either to alter the structure of DNA, or replication, or regulate transcription of DNA into RNA.
Like DNA, RNA is also a chain of nucleotides, but unlike DNA it is more often found in nature as a single-strand folded onto itself, rather than a paired double-strand. RNA is synthesized, from the template of DNA, with the help of an enzyme—RNA polymerase by a process known as transcription.