Write the characteristic features of DNA.

Explanation

(i) If one strand runs in the 5'-3' direction, the other runs in 3'-5' direction and thus are antiparallel (they run in opposite direction) . The 5' end has the phosphate group and 3' end has the OH group.
(ii) The angle at which the two sugars protrude from the base pairs is about `120^(@)`, for the narrow angle and `240^(@)C` for the wide angle. the narrow angle between the sugars generates a minor groove and the large angle on the other edge generates major groove.
(iii) Each base is 0.34 nm apart and a complete turn of the helix comprises 3.4 nm or 10 base pairs per turn in the predominant B form of DNA.
(iv) DNA helical structure has a diameter of 20 Å and a pitch of about 34Å. X-ray crystal study of DNA takes a stack of about 10 bp to go completely around the helix `(360^(@))`. (v) Based on the helix and the distance betweenn each turns, the DNA is of three forms -A DNA, B DNA and Z DNA.