Question

Write any four salient features of the double helix structure of DNA.

Answer 1

Hint: Deoxyribonucleic acid (DNA) is a molecule which is composed of two polynucleotide chains that are coiled around each other to form a double helix carrying the genetic information of an individual. This genetic information gives instruction for development, growth, functioning and reproduction in all known organisms.

Complete answer:

The salient features of the double helix structure of DNA are as follow:
- The structure of the double stranded DNA consists of two polynucleic chains and the backbone of these polynucleic chains is constituted by the sugar phosphate. These both polynucleic chains possess anti-parallel polarity which means that one chain has polarity 5’-3’ and the other chain have polarity 3’-5’.

- There are two strands present in the structure of the DNA and boh are joined together by hydrogen bonds between purines and pyrimidines.

- There are two hydrogen bonds that help to pair adenine with the thymine and guanine always pairs with the cytosine with the help of three hydrogen bonds.

- The two chains of polynucleic are coiled around each other where the pitch of the helix is 3.4 nanometre and the distance between the two base pairs is 3.4A. The sugar and phosphate help in forming the backbone of DNA double helix structure where bases are projecting inwards.

Note: The double helix DNA structure was first published in the journal “Nature” by James Watson and Francis Crick in 1953 based on the work of Rosalind Franklin of the crucial X-ray diffraction image of the DNA labelled as “photo 51”.