Section 3: Genetics, Cellular and Molecular Biology
DNA replication, transcription, translation
Subtopic: Fundamentals of DNA replication, transcription, translation
Question Statement:
Which of the following is/are posttranslational modification(s) involved in
epigenetic control of gene expression?
Options:
(A) Arginine methylation
(B) Lysine acetylation
(C) Cytosine methylation
(D) Cytosine deamination
Official Answer Key:
A;B
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2026 Q.48)**
**1. Governing Concept**:
- **Topic**: Epigenetics & Post-Translational Histone Modifications (PTMs)
- Epigenetic gene regulation frequently involves reversible covalent post-translational modifications of basic amino acid residues on histone tails:
1. **Histone Acetylation**: Catalyzed by Histone Acetyltransferases (HATs) on lysine residues; neutralizes positive charge, loosens chromatin (euchromatin), and promotes transcription.
2. **Histone Methylation**: Catalyzed by Histone Methyltransferases (HMTs) on lysine (Lys) and arginine (Arg) residues; can activate or repress transcription depending on residue and degree of methylation (e.g. H3K4me3 vs H3K9me3).
3. **Histone Phosphorylation**: On serine, threonine, or tyrosine residues; involved in chromosome condensation and DNA repair.
4. **Histone Ubiquitination / SUMOylation**: On lysine residues.
**2. Option Analysis**:
- **Option (A) [Histone methylation] is CORRECT**: A classic epigenetic mark regulating transcriptional repression and activation.
- **Option (B) [Histone acetylation] is CORRECT**: A fundamental epigenetic covalent modification that opens chromatin structure to facilitate transcription factor binding.
- **Option (C) [Peptide bond cleavage by proteases during protein maturation] is INCORRECT**: Proteolytic zymogen activation is irreversible processing, not an epigenetic chromatin regulatory modification.
- **Option (D) is INCORRECT**: Non-chromatin modifications do not constitute epigenetic regulatory mechanisms.
**3. Final Answer**:
- **Correct Options**: **A, B**
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