Ultra Structure of DNA (short notes)

When DNA is studied through electron microscope then it is found that coiling of DNA is same like that of strings of beads.

• Nucleosome: DNA and Histone proteins combine to form nucleosome. In one-nucleosome there are nearly 200 Nucleotides and this DNA duplex is coiled around a core of eight histone proteins.
• Histone: Histone proteins have positive charge, which is different to other proteins in which the charge is negative. The positive charge of histone is due to the presence of abundant basic Amino acid arginine and lysine. The benefit to this Positivity is that these histones and easily attracted towards the negative charged Phosphate groups of DNA.
• Super Coil: When strings of chromosomes more warps up into higher order coils then they are called Super Coil.    

Types of Chromatin: There are two types of Chromatin.

1. Hetrochromatin.
2. Euchromatin. 

Hetrochromatin: This portion of chromatin is highly condensed. Some of its DNA cannot express itself as they are permanently condensed.

Euchromatin: The chromatin other than hetrochromatin is called Euchromatin. It condensed only during cell devision when compact packaging facilities the movement of chromosomes. At the time other than cell division euchromatin is present is an open configuration and its genes can be expressed.