# DBT JRF 2022 — Question 35

Exam: DBT JRF 2022 · Section: A · Topic: Epigenetics › DNA Methylation in Animals · Difficulty: Medium

## Question

The cytosine residues in the DNA are methylated at specific di- or tri-nucleotide sequences. Which among these methylation motifs is predominantly found in case of protein-coding genes in animals? (H stands for A, T or C)

## Options

- **A.** CpG
- **B.** CpHpG
- **C.** CpHpH
- **D.** CpGpG

## Answer

Option A

## Explanation

CpG DNA methylation in animals: In animals (especially mammals), DNA methylation occurs almost exclusively at CpG dinucleotides, where cytosine is methylated at the C5 position by DNMT enzymes: • DNMT3A/3B: de novo methylation • DNMT1: maintenance methylation (copies methylation patterns after replication) Functional implications in protein-coding genes: • CpG islands in gene promoters are typically unmethylated in actively transcribed genes. • Methylation of CpG islands in promoters recruits methyl-CpG binding proteins (MBDs) and HDACs, leading to chromatin compaction and gene silencing. • Gene body methylation (in exons) is actually associated with active transcription and prevents spurious transcription initiation. Contrast: In plants, CpHpG and CpHpH are additionally methylated (see Q4). Answer: CpG (Option 1).

Source: https://mypyqbuddy.com/questions/the-cytosine-residues-in-the-dna-are-methylated-6a104cd5920734408bc0c700