Question

In eukaryotes DNA methylation occurs on:

A) CG or CNG sequences
B) The 5 carbon of the guanine base
C) mRNA
D) Histone octamers associated with nucleosomes
E) Exclusively non-palindromic nucleotides

Answer 1

DNA methylation in eukaryotes primarily occurs on CG or CNG sequences within CpG islands, typically leading to gene silencing or modification of gene expression.

Step-by-step explanation:

In eukaryotes, DNA methylation occurs primarily on cytosine nucleotides that are part of CG dinucleotides or CpG islands. These regions are high in frequency of cytosine and guanine pairs and are typically found in the promoter regions of genes. When a cytosine is methylated, it often leads to gene silencing or other regulatory effects on gene expression. This epigenetic modification changes the interaction between DNA and proteins, such as histones, controlling access to the DNA region for transcription processes. Highly methylated DNA regions tend to be tightly coiled with transcriptionally inactive chromatin, due to the association with deacetylated histones.