20.4 epigenetic control of gene expression Flashcards
what are epigenetics?
heritable changes in gene function without changing base sequence of DNA
what is the epigenome?
epigenetic tags ehich form a second layer on top of DNA & histones
describe the structure of the chromatin when a gene is switched on.
- open chromatin
- unmethylated cytosines
- acetylated histones
describe the structure of the chromatin when a gene is switched off.
- condensed chromatin
- methylated cytosines
- deacetylated histones
where is the acetyl group donated from?
acetylcoenzyme A (link reaction)
how does deacetylation affect gene expression?
- increases positive charges of histone & increases attraction to phosphate groups of DNA
-> stronger attraction between DNA & histone which leads to condensation of DNA-histone complex -> switches gene off
how does methylation affect gene expression?
addition of methyl groups to cytosine bases prevent binding of transcription factors & attracts proteins to induce deacetylation
how are epigenetics linked to diseases?
silencing of a normally active gene / activation of a normally suppressed gene
where does methylation occur?
DNA (cytosine bases)
where does acetylation occur?
histone proteins
how does epigenetic therapy work by?
inhibiting enzymes involved in histone acetylation / DNA methylation
