Methylation

Definition

Methylation is a biochemical process involving the addition of a methyl group (–CH₃) to a molecule, most commonly DNA, affecting gene expression and cellular function without changing the DNA sequence. This process plays a crucial role in epigenetic regulation, influencing how genes are expressed, and can also impact chromatin structure, protein function, and RNA processing.

5 Must Know Facts For Your Next Test

1. Methylation primarily occurs at cytosine residues in DNA, especially in regions known as CpG islands, which are often located near gene promoters.
2. Increased methylation of gene promoters typically leads to gene silencing, while reduced methylation can activate gene expression.
3. Methylation patterns can be heritable, meaning they can be passed down from one generation to another without altering the underlying DNA sequence.
4. Environmental factors such as diet, toxins, and stress can influence DNA methylation patterns and thereby affect gene expression.
5. Methylation plays a significant role in cellular differentiation, helping to determine cell identity by regulating which genes are turned on or off in different cell types.

Review Questions

• How does methylation influence gene expression and what are its potential implications for cellular function?
  • Methylation influences gene expression primarily by adding methyl groups to DNA, particularly at promoter regions. This modification can lead to gene silencing when methylation increases or activation when it decreases. These changes in gene expression can significantly impact cellular functions such as growth, differentiation, and response to environmental signals. Methylation also helps maintain cellular identity by ensuring that only the appropriate genes are expressed in specific cell types.
• Discuss the relationship between DNA methylation and histone modifications in the context of chromatin structure.
  • DNA methylation and histone modifications are closely linked processes that together regulate chromatin structure and gene accessibility. Methylated DNA can attract proteins that further modify histones, often resulting in a more compact chromatin structure that inhibits transcription. Conversely, histone modifications can influence the recruitment of enzymes that add or remove methyl groups from DNA. This interplay ensures that genes are expressed or silenced in a coordinated manner depending on the cellular context.
• Evaluate the potential consequences of altered methylation patterns on human health and disease.
  • Altered methylation patterns can have significant consequences for human health, as they may contribute to the development of various diseases. For instance, hypermethylation of tumor suppressor genes can lead to cancer progression by silencing critical genes that normally prevent uncontrolled cell growth. Similarly, abnormal methylation profiles have been linked to neurological disorders and autoimmune diseases. Understanding these changes could provide insights into disease mechanisms and inform therapeutic strategies aimed at reversing detrimental methylation alterations.

Related terms

DNA methylation:

The addition of methyl groups to the DNA molecule, typically at cytosine bases, leading to the repression of gene expression.

Histone modification: The chemical alteration of histone proteins, including methylation, acetylation, and phosphorylation, which can influence chromatin structure and gene activity.

Post-transcriptional modification: The changes made to RNA molecules after transcription, such as splicing and the addition of a poly-A tail, that can affect mRNA stability and translation efficiency.