Question

Coiling of B DNA duplex is
(a)Left hand
(b)Right hand
(d)Parallel
(d)All of the above

Answer 1

Hint: DNA helix is divided into 3 types based on the structure of the helix. These are A, B, and Z DNA. The most commonly occurring type is the B form of DNA. The structure of this form was shown in the Watson Crick model of DNA helix.

Complete answer:
The coiling of the B DNA helix occurs in the right hand. This type of DNA helix has two antiparallel strands. These two run opposite, one from 5'-3' and the other from 3'-5' and coils around the same axis and forms the right-handed helix.

Additional Information:
DNA double helix is the structure formed by double-stranded molecules of nucleic acids. It arises as a consequence of its secondary structure and is a fundamental component in determining the tertiary structure.
In the case of B DNA, the helix is right-handed with 10-15 base pairs per turn. It is the most common double-helical structure in nature. The major groove of B DNA is wider than the minor groove. The backbone of this DNA is made by the sugar-phosphate sugar chain. The nitrogenous base lies perpendicular to it.
The B form of DNA helix was discovered by Watson and Cruck on the X-ray diffraction patterns. Below are some measurements of B DNA:
-0.34nm between each base pair, 3.4 nm per turn, and 10-15 base pair per turn
-1.9nm in diameter.
-3.4A is the vertical rise per base pair
-Rotation per base pair is +36°
Therefore, the correct answer is the right hand.

Note: The other two types of DNA helix are A and Z type. A is also a right-handed helix whereas Z is left-handed. In the case of A, the dehydrated DNA takes an A form and protects the DNA during conditions like desiccation. In the case of Z, the helix winds to the left into a zig-zag pattern. This form was discovered by Andres Wang and Alexander Rich. It is believed that Z DNA plays some kind of role in gene regulation as well.