Question

Acetylation of histones H3 and H4 is associated with

• A. The activation or inactivation of gene transcription
• B. The chromosomal assembly during DNA replication
• C. The condensation of chromosomes during the replication cycle
• D. The DNA repair

Hint:

Remember:
- Acetylation \(\implies\) Open chromatin \(\implies\) Active Transcription.
- Deacetylation \(\implies\) Condensed chromatin \(\implies\) Repressed/Inactive Transcription.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Covalent modifications of histone tail residues alter the electrostatic interactions between histones and DNA, regulating chromatin accessibility.

Step 2: Detailed Explanation:
1. Histone acetylation is catalyzed by Histone Acetyltransferases (HATs), which transfer acetyl groups to conserved lysine residues on H3 and H4 tails.
2. This addition neutralizes the positive charge of lysine, reducing the affinity between histones and the negatively charged DNA backbone.
3. This relaxes the chromatin structure from a condensed state (heterochromatin) to an open state (euchromatin), facilitating access for transcription factors and RNA polymerase.
4. Conversely, deacetylation by Histone Deacetylases (HDACs) restores the positive charge and leads to transcriptional silencing.
Therefore, histone acetylation is primarily associated with the activation or inactivation (regulation) of gene transcription.

Step 3: Final Answer:
The correct option is 1, which corresponds to "The activation or inactivation of gene transcription".