What is the most common conformation of DNA?

B-DNA is the most common conformation of DNA. Proposed by Watson and Crick, this is the most widely recognized and studied DNA conformation and serves as the basis for understanding several essential biological processes including DNA replication and transcription.B-DNA or B-form DNA is a double helix. It is made up of two strands of DNA that wind around the same axis in a right-hand helical structure. The two strands of the duplex are held together via hydrogen bonding between the bases (in anti-conformation. The two strands of the double helix are antiparallel. They run in opposite directions with the nucleotides on one strand aligning in a 5′ to 3′ orientation and their complementary nucleotides on the opposite strand aligning in a 3′ to 5′ orientation. The plectonemic coiling of the two DNA strands contributes to the distinctive compact and efficient structure of B-DNA.  

B-DNA maintains a consistent diameter throughout its length, primarily due to the complementary base pairing between adenine (A) and thymine (T), and guanine (G) and cytosine (C). This base pairing follows Chargaff’s rules, which state that A always pairs with T and G always pairs with C. The hydrogen bonding between complementary base pairs – A with T and G with C, contributes to the stability of the B-DNA double helix structure.

The B-form DNA helix has distinctive structural traits:

• The diameter of the B-DNA helix is approximately 9 nm and the helix pitch is 34 o. 
• There are approximately 10 base pairs per turn with each helical turn measuring approximately 3.4 nm.
• The distance between base pairs is approximately 34 nm, the base-pair tilt is -6 o, and the twist angle is 36 o.