Double helix Nucleic acid tertiary structure

the double helix dominant tertiary structure biological dna, , possible structure rna. 3 dna conformations believed found in nature, a-dna, b-dna, , z-dna. b form described james d. watson , francis crick believed predominate in cells. james d. watson , francis crick described structure double helix radius of 10 Å , pitch of 34 Å, making 1 complete turn axis every 10 bp of sequence. double helix makes 1 complete turn axis every 10.4-10.5 base pairs in solution. frequency of twist (known helical pitch) depends largely on stacking forces each base exerts on neighbours in chain. double-helical rna adopts conformation similar a-form structure.

other conformations possible; in fact, letters f, q, u, v, , y available describe new dna structure may appear in future. however, of these forms have been created synthetically , have not been observed in naturally occurring biological systems.