In an experiment, $DNA$ is treated with a compound which tends to place itself amongst the stacks of nitrogenous base pairs. As a result of this, the  distancebetween two consecutive base increases. from $0.34- 0.44\,nm$ calculate the length of $DNA$ double helix $($ which has $2 \times 10^9\,bP)$ in the presence of saturating amount of this compound.

What are the structures called that give an appearance as ‘beads­on­string’ in the chromosomes when viewed under electron microscope?

Explain the role of scientist :

$1.$ Watson and Crick  $(1953)$

$2.$ Erwin chargaff

Given below are two statements:

Statement $I$: In prokaryotes, the positively charged DNA is held with some negatively charged proteins in a region called nucleoid.

Statement $II$: In eukaryotes, the negatively charged DNA is wrapped around the positively charged histone octamer to form nucleosome.

In the light of the above statements, choose the correct answer from the options given below:

A given double stranded $DNA$ molecule is $1,00,000$ base pairs long. The length of this $DNA$ molecule will be