[W11] Epigenetics Flashcards
(28 cards)
What is epigenetics?
Heritable changes in gene expression that do not involve changes to the DNA sequence.
What are key features of epigenetic modifications?
- Heritable
- Reversible
- Affected by environment
- Self-perpetuating
What biological processes involve epigenetics?
- Development
- X-inactivation
- Imprinting
- Genome stability
- Aging and cancer
What are the five major hallmarks of epigenetic control?
- DNA methylation
- Chromatin remodeling (nucleosome location)
- Histone variation
- Covalent histone modifications
- Regulatory RNAs
Where does DNA methylation commonly occur?
At cytosines in CpG dinucleotides on both strands.
What enzymes control DNA methylation?
- DNMT3A/3B: de novo methyltransferases
- DNMT1: maintenance methyltransferase
- TET enzymes: active demethylation (5mC → 5hmC)
How is DNA demethylated?
- Passive: Failure to methylate new DNA strands
- Active: Enzymatic removal via TET and base excision repair
What is the functional consequence of DNA methylation?
Methylation usually represses transcription by blocking transcription factor binding or recruiting repressors.
What are CpG islands?
100–2,000 bp regions rich in CpGs, usually located at promoters and normally unmethylated.
What happens when CpG islands are methylated?
The promoter is repressed, and gene transcription is silenced.
What are common histone modifications?
- Acetylation (lysine)
- Methylation (lysine, arginine)
- Phosphorylation (serine)
What enzymes control histone modification?
- HATs / HDACs (acetylation)
- HMTs / HDMs (methylation)
- Kinases / Phosphatases (phosphorylation)
What is the ‘histone code’?
The idea that specific combinations of histone modifications convey distinct functional outcomes.
How do modifications affect chromatin?
- Acetylation: activates transcription (opens chromatin)
- Methylation: context-dependent (can repress or activate)
- Phosphorylation: linked to repair, transcription, cell cycle
What is chromatin remodeling?
ATP-dependent repositioning or restructuring of nucleosomes to make DNA accessible.
What are nucleosome-free regions (NFRs)?
Promoter-adjacent regions often flanked by histone variant H2A.Z for regulatory access.
What are chromatin remodeling complexes?
Multiprotein machines with ATPase subunits that slide, eject, or replace histones.
What is heterochromatin?
Condensed, transcriptionally inactive chromatin marked by H3K9 methylation and HP1 binding.
What is euchromatin?
Open, transcriptionally active chromatin often marked by H3K4 methylation and histone acetylation.
What is position-effect variegation (PEV)?
Variegated gene expression due to spreading of heterochromatin into adjacent genes.
What is genomic imprinting?
Epigenetic silencing of one allele based on parent of origin via methylation during gametogenesis.
When are imprinting marks erased and reset?
Erased in primordial germ cells and re-established in a sex-specific manner.
What syndromes are caused by imprinting defects?
- Prader-Willi syndrome: Deletion in paternal chromosome 15q11
- Angelman syndrome: Deletion in maternal chromosome 15q11
What are the roles of ncRNAs in epigenetics?
Regulate gene expression through chromatin modification, transcriptional silencing, or RNA interference.
