L24 & 25: Epigenetics Flashcards
Define epigenetics.
The study of factors that cause stable and heritable, yet reversiblechanges in the way genes are expressed, without changing the DNA sequence.
What are the three processes that alter chromatin structure?
- Modification of histone proteins
- Chromatin remodelling
- DNA methylation
What is the histone code?
The theory that post-translational modifications define chromatin state.
How are histone modifications inherited?
What is the effect of acetylation on DNA transcription?
Acetylated chromatin = OPEN, transcriptionally ACTIVE
Deacetylated chromatin = CLOSED, transcriptionally REPRESSED
DNA is negatively charged, while histones are positively charged.
Acetylation neutralises the positive charge of the histone, decreasing their affinity for DNA and letting it unwind.
Heterochromatin vs euchromatin?
Heterochromatin = condensed
Euchromatin = unwound
What are nucleosomes?
Nucleosomes are octamers of histone proteins around which approx 147bps of DNA are wrapped. (Made of H2A, H2B, H3 and H4)
H1 histone proteins are linkers between nucleosomes, keeping them together.
What is DNA methylation?
5 methyl C residues interact with histones to promote chromatin condensation.
Most common in CpG dinucleotides. Most genes have GC rich areas in the promoter region, called CpG islands. Methylation of C residues in these islands leads to gene repression.
What are the enzymes involved in DNA methylation?
DNA Methyl-transferases. (DNMTs)
DNMT1 - Maintain established methylation patterns, adding methylation to newly made DNA.
DNMT3a and 3b - Adds NEW DNA methylation patterns.
What is the process of active demethylation?
Ten-elevent translocation (TET)
TET1, TET2 and TET3 convert 5mC to 5-hydroxylmethylcytosine.
TET binds to CpG rich regions to prevent unwanted DNMT activity.
What inactivates X chromosomes in female X-inactivation?
XIST - X Inactivation Specific Transcript
Through methylation.
