Lecture on Epigenetics, Chromatin Remodeling, and DNA Methylation

Overview

Topics Covered: Epigenetics, Chromatin Remodeling, DNA Methylation
Focus: How gene expression is regulated by chemical modifications to chromosomes.

Definition: Changes in DNA that alter gene expression without changing the base sequence.
Key Features:
- Does not involve changes in nucleotide sequence (not mutations).
- Addition of chemical tags to DNA and histones.
- Influenced by environmental factors (diet, smoking, exercise).
- Can be inherited by subsequent generations.
Epigenome:
- Total set of all chemical tags on DNA and histones.
- Reflects lifetime accumulation of environmental signals.

Chromatin:
- Complex of DNA and histone proteins.
- Exists in the nucleus and is essential for DNA packing.
Remodeling Process:
- Alters gene transcription by changing chromatin structure.
- Influences whether chromatin is tightly or loosely packed.
Types of Chromatin:
- Heterochromatin: Tightly packed; inaccessible to transcription machinery.
- Euchromatin: Loosely packed; accessible for transcription.
Role of Chemical Tags:
- Determine the packing state of chromatin.
- Influence gene accessibility and transcription potential.

Process:
- Addition of methyl groups to DNA at CpG sites (cytosine followed by guanine).
- Catalyzed by DNA methyltransferase enzyme.
Effects on Gene Expression:
- Methylation generally inhibits transcription.
- Transcription factors and RNA polymerase binding are blocked or chromatin is condensed.
Reversibility:
- Demethylation: Removal of methyl groups, reversing methylation effects.
- Leads to loosely packed chromatin (euchromatin) and gene expression.

Epigenetic modifications, such as DNA methylation and chromatin remodeling, play crucial roles in regulating gene expression.
Understanding these processes helps in appreciating how environmental factors influence genetic functions beyond the DNA sequence itself.