Chp 13

Genomic imprinting: a process that controls whether certain genes are expressed based on which parent they come from. It's a normal part of gene regulation in mammals. 

• Methylation of cytosine in DNA is primarily responsible for genomic imprinting

Histone Methyltransferases: enzymes that add methyl groups to histone proteins

Demethylation: a chemical reaction that removes a methyl group from a histone protein

Demethylation is carried out by histone demethylases

RNA interference (RNAi) is a natural process that silences genes by degrading messenger RNA (mRNA)

Dicer is an enzyme that cuts long dsRNA molecules (into smaller fragments, which are then used to silence genes, regulate gene expression, or defend against viral infections.

Five important features of epigenetic modification:

• epigenetic modification patterns alter chromatin structure

• transmissible during cell division

• reversible

• directly associated with gene transcription

• do NOT alter DNA sequence

Cis-acting regulatory sequences: can control gene expression on the same chromosome as the genes they regulate

Trans-acting regulatory proteins: can control gene expression on multiple chromosomes

Pioneer factors: transcription factors that can bind to condensed chromatin, which helps regulate gene expression

DNase I hypersensitivity sites: regions of the genome that are particularly sensitive to digestion by the enzyme DNase I. These sites are typically found in open chromatin

- The primary function of the SWI/SNF complex is to open chromatin structure by displacing or ejecting nucleosomes.

- HP-1 binds to methylated histones and stimulates heterochromatin formation to silence transcription.

- Covered promoters tend to be associated with genes whose transcription is regulated (not constitutively expressed).

- Enhancers may be located tens of thousands of nucleotides away from the genes they regulate.

- Increased acetylation of histones are typically associated with gene activation and euchromatin formation.