What is the role of histone modification in gene regulation?

• A. They chemically modify histone tails to directly bind to DNA sequences.
• B. Modifications like acetylation and methylation alter chromatin structure and transcription accessibility.
• C. They change the DNA sequence of genes.
• D. They only repress transcription and never activate it.

Answer: (B)

Histone modifications regulate gene expression by changing how tightly DNA is packaged and by guiding other proteins that control transcription. When histone tails are acetylated, the added acetyl groups neutralize positive charges on histones, loosening the DNA-histone interaction. This opens up the chromatin and makes genes more accessible to transcription factors and RNA polymerase, increasing transcription. Methylation, on the other hand, can either promote or repress transcription depending on the specific amino acid that’s modified and the context, by attracting proteins that either open chromatin or compact it. In short, these chemical tags don’t change the DNA sequence or directly bind to DNA; they shape chromatin structure and recruit factors that determine whether a gene is on or off. That’s why the role of histone modification is to alter chromatin structure and transcription accessibility.