Question

Chemical modifications of histone tails are often made in chromatin to change the amount of chromatin compaction. Name three chemical modifications that have been observed by scientists to be on histone tails in chromatin. the modifications that you listed and discuss whether that modification is associated with closed or open chromatin.

Answer 1

Type of chemical modification	enzymes involved	effect on the packing of chromatin	effect on the rate of transcription
Phosphorylation	phosphate group is added by kinases and removed by phosphatases	in general it has a duel effect on the packing of chromatin	it can either lead to an increase or decrease in the rate of transcription of genes
Acetylation	acetyl group is added by acetyltransferases and removed by deacetylases	generally it makes chromatin loose	loosening of chromatin leads to the greater access ability of RNA polymerase towards the gene and therefore increasing the rate of gene expression or transcription
Methylation	methyl group is added by methyltransferases and removed by methylases	generally it makes chromatin compact	tightening of chromatin leads to a decrease in the accessibility of RNA polymerase for the genes and therefore the rate of transcription decreases

Whenever methyl groups are added to the chromatin, then all of them interact with each other in such a way that it leads to tight packing of chromatin. This tight packing of chromatin hides the promoter region of gene. This prevents RNA polymerase from binding to the promoter and transcribing the gene.

Whenever acetyl group are added to the chromatin, they lose the chromatin. This lead to the exposure of the promoter and therefore RNA polymerase can easily bind to the promoter and transcribe the gene.

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