The one which is capable of self replication is

$DNA$ is double helix and

The reason for double helical structure of $DNA$ is operation of

Definitions/Explanation : Histone octomer & Euchromatin
 

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.