Methylation

Definition

Methylation is a biochemical process that involves the addition of a methyl group (–CH₃) to DNA, typically at cytosine bases within a CpG dinucleotide context. This modification plays a critical role in regulating gene expression, influencing the binding of transcription factors and the accessibility of chromatin, thereby impacting cellular processes and development.

5 Must Know Facts For Your Next Test

1. Methylation can lead to gene silencing by preventing transcription factors from binding to DNA, thereby reducing gene expression.
2. In normal development, specific patterns of methylation are established and maintained, influencing cellular differentiation and identity.
3. Abnormal methylation patterns are associated with various diseases, including cancer, where hypermethylation can silence tumor suppressor genes.
4. Methylation patterns can be inherited from one generation to another, indicating that epigenetic information can influence phenotypes without altering the DNA sequence.
5. Environmental factors, such as diet and exposure to toxins, can influence methylation patterns and subsequently affect gene expression.

Review Questions

• How does methylation influence the binding of transcription factors to DNA?
  • Methylation directly affects the binding of transcription factors by adding a methyl group to cytosines in the DNA sequence. When methyl groups are present at promoter regions, they can hinder the access of transcription factors required for initiating transcription. This restriction limits gene expression, demonstrating how methylation serves as a regulatory mechanism in gene control.
• Discuss the relationship between methylation and chromatin structure in gene regulation.
  • Methylation plays a significant role in modifying chromatin structure by influencing how tightly or loosely DNA is wrapped around histones. When methyl groups are added to certain sites on DNA, it can lead to a more compact chromatin state known as heterochromatin, making the DNA less accessible for transcription. This change in chromatin structure is crucial for regulating gene expression patterns in different cell types and during development.
• Evaluate the implications of altered methylation patterns in the context of disease development, particularly cancer.
  • Altered methylation patterns have profound implications for disease development, particularly in cancer. Hypermethylation of promoter regions can lead to silencing of tumor suppressor genes, enabling unchecked cell growth and proliferation. Conversely, hypomethylation can activate oncogenes. These changes contribute to the cancer phenotype and highlight the importance of studying methylation as a target for therapeutic interventions aimed at re-establishing normal gene expression patterns.

Related terms

CpG Islands:

Regions of DNA that have a high frequency of cytosine and guanine nucleotides adjacent to each other, often found near the promoters of genes and are typically unmethylated in active genes.

Histone Modification: The post-translational modification of histone proteins, including methylation, acetylation, and phosphorylation, which affects chromatin structure and gene regulation.

Epigenetics: The study of heritable changes in gene expression that do not involve changes to the underlying DNA sequence, including mechanisms like methylation and histone modification.