Q.2 Which one of the following modifications is common toboth protein and DNA?
(A) SUMOylation (B) Nitrosylation (C)Methylation (D) Ubiquitination
Methylation stands out as the common modification linking proteins and DNA, regulating gene expression and function in both. This MCQ tests foundational knowledge in epigenetics and post-translational modifications, crucial for biotech and molecular biology exams.
Correct Answer
C) Methylation is the shared modification. DNA undergoes cytosine methylation at CpG sites by DNMT enzymes, silencing genes epigenetically. Proteins, especially histones, receive lysine/arginine methylation via PRMTs or KMTs, altering chromatin structure.
Option Analysis
(A) SUMOylation
SUMOylation conjugates SUMO proteins to lysine residues on target proteins, modulating stability and interactions. Exclusive to proteins; DNA lacks this machinery.
(B) Nitrosylation
Nitrosylation adds nitric oxide to cysteines in proteins, enabling redox signaling. No equivalent exists in DNA modification pathways.
(D) Ubiquitination
Ubiquitination tags proteins with ubiquitin chains for degradation via proteasome. Primarily protein-specific; DNA does not undergo this.
Biological Relevance
Methylation dynamically controls transcription: DNA methylation recruits repressors, while histone methylation (e.g., H3K4me3 activates, H3K27me3 represses). This crosstalk forms the epigenetic code, essential for development and disease.
