Acetylation of histones increases which form of chromatin and thereby increases which process?

• A. Heterochromatin; Transcription
• B. Euchromatin; Transcription
• C. Euchromatin; Replication
• D. Heterochromatin; Replication

Answer: (B)

Histone acetylation loosens chromatin structure to make DNA more accessible for transcription. When acetyl groups are added to lysine residues on histone tails, the positive charges are neutralized, weakening the interaction between histones and the negatively charged DNA. This reduces nucleosome compaction, shifting chromatin from a closed, condensed state (heterochromatin) toward a more open form (euchromatin). Euchromatin is accessible to RNA polymerase II and transcription factors, so transcription increases. While replication also benefits from accessible chromatin, the primary effect of acetylation is to promote transcription, not to actively increase replication, and heterochromatin—being compact and repressive—would not be enhanced by acetylation.