BIO 351 Lecture Notes - Lecture 13: Euchromatin, Dna Polymerase, Nucleosome
Epigenetics Objective
1. Give some examples of proteins that need to access genes for transcription. How are these DNA-protein
interactions affected by chromatin structure? *
− In Eukaryotes, chromatin has the ability to coil more loosely or more tightly according to chemical
modifications
o This is separate from condensing into chromatids though, that only happens for mitosis
o Continuum of tightness from euchromatic to heterochromatic
o Proteins only have access to DNA if in the euchromatic form
o Genes are silenced in the heterochromatic form
− There are lots of proteins that need access to DNA to start the transcription of genes
o TAP, TF, DNA Polymerase, RNA Polymerase, mismatch and damage repair enzymes, Xist RNA,
inhibitory proteins, anything in a signal transduction pathway, etc.
2. What are the chemical modifications to DNA and histones that influence chromatin structure? (Methylation,
acetylation, DNA, histones)
3. Review the structure of nucleosomes focusing on the N-teial as of histoes.
− Nucleosome = 8 core histones wrapped around DNA twice
o Core histones = 2 each of H2A, H2B, H3, H4
▪ Proteins that are responsible for the coiling and protection
of Eukaryotic DNA
o Linker DNA = H1 and H5
▪ Anchor to DNA and stabilize coiled formation
− C Terminus of histones is conserved and pivotal to the nucleosome
− N Terminus of histones arms have variable interactions among nucleosomes according to chemical
modifications
o Cotols thei stikiess ad the pesoalit of ho the interact and coil together
o Lsie aio aid K is e audat i N teial etesios ad ae ofte the ai
player/recipient of acetylation and methylation
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Document Summary
Epigenetics objective: give some examples of proteins that need to access genes for transcription. C terminus of histones is conserved and pivotal to the nucleosome. Dna methylation: cpg methylase associated with heterochromatin/silencing, cpg demethylase associated with euchromatin/expression, methylation distorts dna double helix and proteins cannot access/ bind to dna. Histone methylation: histone methyltransferase (hmt) associated with heterochromatin/silencing, histone demethylase (hdm) associated with euchromatin/expression, trend below from left to right is increasing affinity to dna and other histones (sticky!) Cpg islands are sites of high dna methylation by cpg methylase. High dna methylation makes the dna heterochromatic/warped and inaccessible to proteins. This decreases expression or completely silences genes. By having these sites of high methylation in the promoter region of transcription, there is the ability to regulate the genes through epigenetics. What do i(cid:373)p(cid:396)i(cid:374)ted genes have in common? (maternal copy, paternal copy, silencing) Imprinting = the cell selectively silences one copy of an autosome.
