What is required for the packaging of chromatin at a higher level?

$A$ $DNA$ polymer has a free phosphate group at one end of the sugar,which is called the $P$ end of the polynucleotide chain. Similarly,at the other end of the polymer,there is a free $OH$ group of the sugar,which is called the $Q$ end of the polynucleotide chain.
$\quad P \quad Q$

$NHC$ (Non-Histone Chromosomal) structural proteins are:

In the structure of $DNA$,if a purine base is present on one nucleotide strand,which nitrogenous base pairs with it?

Chargaff's rule is given as:

The terms $Gene$ and $Cistron$ are often used as synonyms because...