Hey guys, today I’m going to discuss you
about nucleosome solenoid model. Now, what is nucleosome?
Nucleosome is a small part of chromosome. In past it was called as gamma body. The word nucleosome was first coined by Outdet.
In 1974 R. Kornberg and Thomas published Nucleosome solenoid model.
What is nucleosome solenoid model? In this model you can see chromatosome which consist of three parts Nucleosome : It consist of two parts
Nucleosomal DNA which consist of 146 BP
and core Histone protein Which consists of 4 types of Histone Protein Like H2A, H2B, H3 and H4 And the total number of Histone protein is 8. And in a chromatosome total number of Histone protein is 9 with added H1 protein. So the total number of nitrogen base in a chromatosome is 200 The Nucleosome has egg like shape. It has 110A diameter and 60A height. Now the Arrangement of that histone protein in core
particle If you imagine a cube there are three opposite
plains. From there I’m taking one opposite plain. I indicate those plains as num 1 and
num 2. In no. 1 plain from point O, I arrange 4 histone
proteins in anti clock wise manner one by one like H2A,
H2B, H3 and H4. Likewise another plain from point P those
histone protein are arranged anti clock wise in this manner
H2A, H2B, H3 and H4. So if you see this diagram same proteins are places in opposite corner
of a plain. These proteins are joined together. So a steric
hindrance repulsion is produced. But these are attached tightly for two reason- a sterio
specific bond. another Nucleioplasmin protein which is anionic
in nature. This stables the structure. This core particle is surrounded by nucleosomal
DNA in 1 and 3/4th round and joined with H1protein. And together all of these are called chromatosome. nucleosomes are linked by linker DNAs
and make oligonucleosome. This linker DNA is also called spacer DNA. Some Oligonucleosomes
make a chromatin fiber width of 10 nm. H1 proteins are located towards the centre of
oligonucleosome. For this reason interaction of H1 proteins occurs.
this interaction of H1 protein occurs For H1 -H1 protein Repulsion force
and the Electrostatic Attraction of H1 protein and DNA Reason of this attraction is DNA is negatively charged due to phosphate ions and histone
is positively charged due to arginine, histidine, lysine. 6 nucleosomes are joined together and make a solenoid of 30nm of diameter. In this
solenoid there is some scaffold attachment regions (SAR). SAR is the specific area where
adenine and thymine are found in plenty numbers Scafol protein joins in SAR region and makes
a super solenoid model of 300 nm of diameter. This fiber is highly condensed and makes chromatid
fiber of 700nm of diameter. In metaphase this fiber is highly condensed
and makes a chromosome of width of 1400nm. Now some extra information about H protein
You know very well that prokaryotic cell has no histon protein but only in e. choli
there is HU protein is found which acts like H1 protein and H2 protein.
This is all about nucleosome solenoid model. Next time I’ll be back with some useful
topics of biology