Question

Discuss how histones and nucleosomes interact with DNA and effects of acetylation and methylation incliding it's epigenetic effects.

Answer 1

The DNA is super coiled and compacted in the structure called as Nucleosome which is a small part of chromosome. This nucleosome along with histones proteins is called as chromatosome. The nucleosome containing DNA is tightly wrapped around histones proteins, around 4 histone proteins are arranged one above the other and nucleosome is wrapped around histones prtoeisn. As histone proteins are positively charged with amino groups DNA is tightly bonded to histoens proteins due to negative charge of DNA. This tight bond makes DNA unavailable for the transcription.

Acetylation helps unwrapping the DNA from hitosnes molecules making DNA available for the transcription and this is den by the enzyme acetyl histone transferase.Which acetyl group to C terminal of hitsone proteins.

In methylation the histone 3 residues arginine are attack and makes the DNA completely wrapped making DNA completely unavailable for transcription Example X inactivation can be seen in the zygotes were zygote receives X chromosomes from both parents Hence methylation inactivates one foe X chromosomes receives from one of parent thus how methylation works.

In epigenetic modification acetylation and methylation plays a important by activating the gens by unwrapping the nucleosome in particular cell or tissue which is required in that particular cells or tissue example gens which are not requried in liver cells are not turned on but which ere required for liver functions are turned on.