Histone acetylation

Definition

Histone acetylation is a biochemical process where an acetyl group is added to the amino acids of histone proteins, leading to changes in chromatin structure and gene expression. This modification typically promotes a more relaxed chromatin state, making the DNA more accessible for transcription and thereby influencing gene regulation.

5 Must Know Facts For Your Next Test

1. Histone acetylation is catalyzed by enzymes known as histone acetyltransferases (HATs), which add acetyl groups to lysine residues on histones.
2. This process is reversed by histone deacetylases (HDACs), which remove the acetyl groups and can lead to transcriptional repression.
3. Acetylation neutralizes the positive charge on lysine residues, reducing the interaction between histones and negatively charged DNA, leading to a more open chromatin structure.
4. Histone acetylation is associated with active transcription, as it creates a permissive environment for the binding of transcription factors and the transcriptional machinery.
5. The pattern of histone acetylation can vary across different cell types and developmental stages, contributing to cell-specific gene expression profiles.

Review Questions

• How does histone acetylation affect chromatin structure and gene expression?
  • Histone acetylation leads to a more relaxed chromatin structure by neutralizing the positive charges on lysine residues in histones. This change allows for increased accessibility of DNA to transcription machinery, promoting gene expression. When acetyl groups are added by histone acetyltransferases, it enhances the likelihood that genes will be transcribed, illustrating the direct link between this modification and active gene regulation.
• Discuss the role of histone acetyltransferases and histone deacetylases in regulating gene expression through histone acetylation.
  • Histone acetyltransferases (HATs) add acetyl groups to histones, facilitating a more open chromatin structure that promotes gene expression. Conversely, histone deacetylases (HDACs) remove these acetyl groups, leading to tighter chromatin packing and repression of gene activity. The balance between HAT and HDAC activity is crucial for maintaining proper gene expression patterns, allowing cells to respond to various signals and environmental changes.
• Evaluate the implications of altered histone acetylation patterns in disease contexts such as cancer.
  • Altered patterns of histone acetylation can have significant implications in diseases like cancer, where dysregulation of gene expression is common. For instance, overactivity of HATs may lead to excessive gene activation, contributing to oncogene overexpression, while reduced HDAC activity can result in silencing of tumor suppressor genes. Understanding these alterations provides insights into potential therapeutic targets for epigenetic drugs aimed at restoring normal gene regulation in cancer cells.

Related terms

Chromatin: The complex of DNA and proteins, primarily histones, that forms chromosomes within the nucleus of eukaryotic cells.

Histone Deacetylation: The removal of acetyl groups from histones, which generally leads to a more condensed chromatin structure and reduced gene expression.

Transcription Factors: Proteins that bind to specific DNA sequences to regulate the transcription of genes, often interacting with histone modifications like acetylation.