How does a methyl group affect the expression of genes?

A methyl group can significantly alter gene expression through a process known as methylation, specifically DNA methylation. When methyl groups are added to certain regions of DNA, particularly in the promoter regions of genes, it can lead to the repression of gene expression. This is because the presence of methyl groups can hinder the binding of transcription factors and other essential proteins required for the initiation of transcription. The addition of methyl groups can also affect the three-dimensional structure of the DNA, making it more compact and less accessible for transcriptional machinery.

This means that methyl groups can play a crucial role in gene regulation and are involved in various biological processes, including development, differentiation, and the maintenance of cellular identity. Moreover, abnormal DNA methylation patterns are frequently associated with diseases, including cancer, highlighting the importance of methylation in gene expression and regulation.