How does epigenetic modification control gene expression?

Epigenetic modification controls gene expression by adding or removing chemical groups to DNA or histone proteins.

Epigenetic modification is a biological process that alters the physical structure of DNA, thereby influencing gene expression. This does not involve changes to the underlying DNA sequence, but rather the addition or removal of chemical groups. These modifications can either activate or silence genes, thus controlling their expression.

There are two main types of epigenetic modifications: DNA methylation and histone modification. DNA methylation involves the addition of a methyl group to the DNA molecule, typically at a cytosine base. This usually results in the silencing of the gene, as it prevents the transcription machinery from accessing the DNA and producing mRNA. This is a crucial process in cellular differentiation, where cells become specialised for their specific functions.

Histone modification, on the other hand, involves the addition or removal of chemical groups to histone proteins around which DNA is wound. These modifications can alter the structure of the histone, making the DNA more or less accessible for transcription. For example, acetylation of histones usually results in gene activation, as it loosens the DNA around the histones, making it easier for the transcription machinery to access the DNA. Conversely, methylation of histones can either activate or repress gene expression, depending on the specific context.

Epigenetic modifications are heritable, meaning they can be passed on from cell to cell during cell division, and from parent to offspring during reproduction. However, they are also reversible, allowing for flexibility in gene expression. This is crucial for processes such as development and adaptation to environmental changes.

In summary, epigenetic modifications control gene expression by altering the physical structure of DNA or histones, thereby influencing the accessibility of the DNA for transcription. These modifications are crucial for cellular differentiation, development, and adaptation to environmental changes.