Question

Why does histone deacetylase action tend to repress

transcription?
A. Removal of acetyl groups from lysine residues in histones
yields positively charged free amino groups, which form ionic
interactions protein repressors.
B. Removal of acetyl groups from lysine residues in histones yields
positively charged free amino groups, which interfere with the
ionic interaction with negativly charged mediator.
C. Removal of acetyl groups from lysine residues in histones yields
positively charged free amino groups, which form ionic interactions
with negatively charged DNA phosphates.

Answer 1

Option-C

Step-by-step explanation:

The histone modification plays an important role in the epigenetic expression of the DNA that is it acts as a switch for transcription.

The histone proteins contain positive amino acids at the end called arginine and lysine. The positive charge on these amino acids helps bind the histone to negatively charged DNA.

When deacetylase binds the histone, it removes the acetyl group from the lysine which increases the positive charge on the histone thereby binding the "phosphate of DNA" which are negatively charged more tightly. This switch off the transcription.

Thus, Option-C is the correct answer.

Histone tails are normally positively charged due to amine groups present on their lysine and arginine amino acids. These positive charges help the histone tails to interact with and bind to the negatively charged phosphate groups on the DNA backbone. Acetylation, which occurs normally in a cell, neutralizes the positive charges on the histone by changing amines into amides and decreases the ability of the histones to bind to DNA. This decreased binding allows chromatin expansion, permitting genetic transcription to take place. Histone deacetylases remove those acetyl groups, increasing the positive charge of histone tails and encouraging high-affinity binding between the histones and DNA backbone. The increased DNA binding condenses DNA structure, preventing transcription