epigenetics

/Epigenetics - Study Notes

Definition

• Epigenetics: The study of heritable changes in gene expression or cellular phenotype that do not involve changes in the DNA sequence.

Key Concepts

• Gene Expression Regulation: Epigenetic modifications affect how genes are turned on or off, influencing development and disease.

• Mechanisms:

• DNA Methylation: Addition of a methyl group (-CH3) to DNA, usually silencing gene expression.

• Histone Modification: Changes to histones that affect the tightness of DNA packaging, influencing gene accessibility.

• Acetylation: Histone acetylation usually activates gene expression by loosening DNA packaging.

• Methylation: Histone methylation can either activate or repress gene expression depending on context.

Key Epigenetic Modifications

• DNA Methylation:

• Occurs mainly at CpG sites (regions where cytosine is followed by guanine).

• Associated with gene silencing.

• Mechanism: Methyl groups inhibit transcription factors, making DNA inaccessible.

• Histone Modification:

• Acetylation: Addition of acetyl groups to histones, reducing DNA packaging and activating gene expression.

• Methylation: Can lead to either gene silencing or activation, depending on which histone is modified and the context.

Nucleosome Remodeling

• Histone modifications lead to nucleosome sliding (rearrangement of histone proteins), which affects the tightness of DNA packaging, altering gene expression.

Factors Affecting Epigenetics

• Environmental Factors: Diet, toxins, stress, and other environmental influences can affect epigenetic modifications, potentially leading to changes in gene expression that are passed down to offspring.

Example: Agouti Mice

• Agouti Gene: Epigenetic modifications of the agouti gene lead to different fur colors in mice.

• Methylation of the agouti gene can result in brown fur, while lack of methylation leads to yellow fur.

• Environmental factors, such as diet, can influence methylation patterns and fur color.

Applications

• Development: Epigenetics plays a role in stem cell differentiation, where different cells express different genes despite having identical DNA.

• Diseases: Abnormal epigenetic modifications can lead to diseases like cancer, where genes involved in cell growth or apoptosis are either overexpressed or silenced.

• Inheritance: Epigenetic changes can be passed down through generations without altering the underlying DNA sequence.

Summary

• Epigenetic modifications regulate gene expression without changing the DNA sequence.

• DNA methylation and histone modifications are the main mechanisms.

• These changes can be influenced by environmental factors and passed down to offspring.

• Epigenetics is crucial in development, disease, and inheritance.