Write the characteristic features of DNA.

Explanation

1. 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.
2. The angle at which the two sugars protrude from the base pairs is about `120^(@)`, for the narrow angle and `240^(@)` 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.
3. Each base is 0.34 nm apart and a complete tum of the helix comprises 3 .4 nm or 10 base pairs per tum in the predominant B form of DNA.
4. DNA helical structure has a diameter of `20A^(@)` and a pitch of about `34A^(@)` X-ray crystal study of DNA takes a stack of about 10 bp to go completely around the helix `(360^(@))`.
5. The phosphodiester linkages gives an inherent polarity to the DNA helix. They form strong covalent bonds, gives the strength and stability to the plolynucleotide chain.
6. Plectonemic coiling - The two strands of the DNA are wrapped around each other in a helix, making it impossible to simply move them apart without breaking the entire structure. Whereas in paranemic coiling the two strands simply lie alongside one another, making them easier to pull apart.
7. Based on the helix and the distance between each turns the DNA is of three forms- A-DNA, 8-DNA and Z-DNA.