Question

Basic structure of chromatin is composed of
A. Non-histone proteins wrapped around DNA
B. Histone proteins wrapped around DNA
C. RNA wrapped around histones
D. DNA wrapped around histones

Answer 1

Hint:- DNA is the genetic material present in higher organisms. It is an acidic substance that is present in the nucleus and is negatively charged. It was first discovered by the scientist Friedrich Meischer in 1869.

Complete step-by-step solution:-
The length of DNA in organisms could be so large that it needs to be packed in a way to get fitted in a small area. DNA is a negatively charged molecule and in prokaryotes, held by some positively charged proteins in a region known as ‘nucleoid’.
In the eukaryotes, the organization of DNA is more complex. Similar to prokaryotes, in eukaryotes also DNA is packed with the help of positively charged proteins known as histones. Histones are proteins that are rich in basic amino acid residues of lysine and arginine. Histone carries eight molecules together and is called histone octamer. The DNA gets wrapped around the histone octamer and this structure is known as ‘nucleosome’. In a single nucleosome, 200 base pairs of DNA helix are arranged. Chromatin is a thread-like fibrous structure in the nucleus. A repeating unit of nucleolus constitutes chromatin.
Thus the correct option is (D) DNA wrapped around histones.

Additional information:- Under an electron microscope, the nucleosome in the chromatin looks like a ‘beads-on-string’ structure which is its identifying characteristic. Beads-on-string structure is useful in packaging it further with the help of additional proteins known as non-histone proteins.

Note:- Some regions of chromatin are loosely packed (lightly stained) in the nucleus and are called euchromatin, whereas other regions that are densely packed and darkly stained are known as heterochromatin.