Question

Discuss in detail one method of epigenetic regulation of transcription.

Answer 1

Ans) Histone tail modifications can occur in order to express or inhibit the gene expression in the cells.Histone modifications like acetylation of lysine,methylation of lysine and arginine,phosphorylation of serine,threonine,ADP-ribosylation of glutamic acids,Ubiquitylation of lysine,Sumoylation of lysine residues etc can occur. We will discuss acetylation in detail.

Histone acetylation is catalyzed by the enzyme Histone acetyltransferase (HAT) which adds acetyl groups (negatively charged) on the histones on the DNA.DNA is negatively charged due to the presence of phosphate groups in the sugar-phosphate backbone.After the addition of acetyl groups,there will be repulsion due to negative-negative interactions and the histones will loosely bind to DNA.Due to this,RNA polymerase can easily access the promoter sequence and start Transcription.In acetylation, open chromatin structure or Euchromatin is formed and thus gene expression occurs.

HDAC (Histone deacetylase) enzyme removes acetyl groups from the histone and now due to positive-negative interactions between Histones and DNA leads to tight binding and now the RNA polymerase cannot access the promoter sequence and the Transcription is inhibited and thus no gene expression.