Statement–I is incorrect but Statement–II is correct. Histone acetylation promotes gene transcription by loosening chromatin, while acetylation specifically targets lysine residues in histone tails.
Statement Analysis
Statement–I: False. Histone acetylation neutralizes positive charges on lysines, reducing histone-DNA affinity and opening euchromatin for transcription factor access—increasing, not decreasing, transcription.
Statement–II: True. Acetylation by HATs occurs on ε-amino groups of lysine residues (e.g., H3K9, H3K14, H4K16) in the flexible N-terminal tails protruding from nucleosomes.
Option Breakdown
| Option | Explanation |
| Both correct | Wrong: I false . |
| Both incorrect | Wrong: II true . |
| I correct, II incorrect | Wrong: I false, II true . |
| I incorrect, II correct | Correct: Matches analysis . |
Histone acetylation gene transcription link is key for NEET Life Sciences—acetylation on lysine residues opens chromatin, boosting (not decreasing) expression contrary to Statement I.
Mechanism Details
Acetyl groups from acetyl-CoA (via HATs like p300/CBP) attach to lysine ε-amino groups in histone tails. This reduces positive charge, weakening DNA-histone electrostatic bonds and recruiting bromodomain proteins for active transcription.
HDAC Counteraction
HDACs remove acetyl groups, restoring positive charges and condensing chromatin to repress genes. Balance controls development, cancer, neurodegeneration.
Exam Focus
Assertion-reason questions test “effect” (activation) vs. modification site (lysines). Common traps: confusing acetylation (activation) with methylation (can repress/activate).
