Hi Abhash!

I am listing down some of the salient features of the polynucleotide chains:

1. Two polynucleotide chains constitute the double helical structure of DNA.

2. The backbone of the polynucleotide chain is composed of sugar and phosphate group while the nitrogenous bases project inwards.

3. The bases in the two strands of polynucleotide chains show pairing through H-bonds. e.g. Adenine pairs with Thymine through 2 H-bonds while Guanine pairs with Cytosine through 3 H-bonds.

4. The polynucleotide chains run anti-parallelly. That means, if one polynucleotide chain has 5'-3' polarity the other will have 3'-5' polarity.

5. The two polynucleotide chains are coiled in a right-handed manner. 

6. The length of one complete turn is 3.4 nm.

7. One complete turn has 10 base pairs.

8. Therefore, the distance between two base pairs is 3.4/10 = 0.34 nm.

9. The plane of one base pair stacks over another base pair in the double helix DNA structure, rendering it more stability.

Thanks