Nuclear Chromatin

Introduction :   It is a clearly stained, network of long and fine threads (called chromatin fibers) suspended in nucleoplasm largely in the interphase nucleus. W. Flemming (1879) first discovered by during cell division, these chromatin fibers condense by spiralization and dehydration into number of rods called chromosomes (Waldayer (1888)  DNA is main genetic component of all cells carrying information in a coded form from one cell to another DNA is not found free but compressed/associated with proteins in structure called (Viromatin (DNA+ Proteins)

Subtitle – 1.    When the structures, were separated and analysed biochemically, it appered to contain DNA, RNA, basic proteins called Histones and acidic proteins called Non- Histones.

Since early 1960’s, it was shown that content of RNA and non – histone protein is variable in different chromatin preparation Histone and DNA are always present in fixed ratio of 1:1 The non – histone proteins are very heterogenous and include enzymes like DNA and RNA  polymerases and some regulatory proteins. On the other hand, there are five – Types of Histone proteins present :

Such one present in large amounts.

• Histones are small proteins that are basic in nature because they have a high content of basic amino – acids like Arginine and Lysine. Being Basic in nature, histones bind tightly to DNA molecule which is acidic in nature amongst five – histone molecules, four main histones i.e. H2A, H2B, H3, and H4 are most conserved proteins (due to similar amino acid composition). H1 is not well conserved between species and it is tissue specific, It is found only once per every 200 base pairs of DNA and loosely association with chromatin.