Read the given passage and answer the following question :

In 1953 that James Watson and Francis Crick, based on the X-ray diffraction data produced by Maurice Wilkins and Rosalind Franklin, proposed a very simple but famous Double Helix model for the structure of DNA. One of the hallmarks of their proposition was base pairing between the two strands of polynucleotide chains. However, this proposition was also based on the observation of Erwin Chargaff that for a double stranded DNA, the ratios between Adenine and Thymine and Guanine and Cytosine are constant and equals one. The base pairing confers a very unique property to the polynucleotide chains. They are said to be complementary to each other, and therefore if the sequence of bases in one strand is known then the sequence in other strand can be predicted.

What is the distance between two successive nitrogenous base pairs in DNA  molecule ?

0.34nm/3.4 A⁰

The correct answer is Option (2) - 0.34nm/3.4 A⁰

The DNA molecule consists of two polynucleotide chains that form a double helix structure. The DNA double helix is a right-handed helix, meaning the strands twist around each other in a right-handed manner along a common axis.The Double-helix structure of DNA  is made of two polynucleotide chains, where the backbone is constituted by sugar-phosphate, and the bases project inside. The two chains have anti-parallel polarity. It means, if one chain has the polarity 5'-3', the other has 3'-5'. The bases in two strands are paired through hydrogen bond (H-bonds) forming base pairs (bp). Adenine forms two hydrogen bonds with Thymine from opposite strand and vice-versa. Similarly, Guanine is bonded with Cytosine with three H-bonds. As a result, always a purine comes opposite to a pyrimidine. This generates approximately uniform distance between the two strands of the helix . The two chains are coiled in a right-handed fashion. The pitch of the helix is 3.4 nm (a nanometre is one billionth of a metre, that is 10-9 m) and there are roughly 10 bp in each turn. Consequently, the distance between a bp in a helix is approximately 0.34 nm.