Biochem-Ch4 (Eukaryotic Transcription)

I am in 15th grade.

Rett Syndrome

HDAC recruited which leads to chromatic condensation and transcription repression

• muscle weakness, difficultly speaking/walking

Heterochromatic

DNA not accessible here so no transcription

• more condensed chromatic here (10% cells)

• constitutive (always), facultative (depends)

Euchromatic

less condensed chromatic where transcription occurs

Nucleosome

basic unit of chromatic

• 8 histones (+ charge) and histone (H2 A/B, H3, H4) core

  • H1 locks DNA in place like thumb to nucleosome

  • Tails contact other nucleosomes

• “beads on a string”

Epigenetics

modifications to chromatic or DNA that don’t affect DNA sequence of bases (genetics)

• affects expression of genes

• can be affected by environment

Histone Acetyltransferase (HAT)

adds acetyl group ( O-CH3) to loosen DNA and this increases transcription

Histone Deacetylase (HDAC)

removes acetyl groups from histone tails, decreases transcription

Hypermethylation

closed chromatin

• Histone Methyltransferase (HMT) methylates K/R in histone tails

Histone Code

H2BK5ac or H3K4me

CpG island

stretches of DNA with lots of “CG” pairs

• if unmethylated, transcription goes ahead

• if methylated, transcription can’t occur

Enhancers

DNA regions that bind activator proteins to greatly increase transcription, even from far away

Classical Zinc finger

small, zinc-stabilized protein loops that let transcription factors bind DNA

Nuclear receptor zinc finger

paired zinc finger domains that help hormone receptors bind DNA and dimerize

SWI/SNF

uses ATP to move nucleosomes and open chromatin, increasing transcription

Coactivators

facilitate communication btwn activators and complex of Pol II and general transcription factors

• Mediators: bridge everything together

RNA Polymerase II

synthesizes mRNA and ncRNA

• rna pOL i- Rrna

• rna Pol III- tRNA

Transcription Factors

array of proteins that work with Pol II form active transcription complex

• TFII…

Locating Promoters

• TFIID: made of TBP & TAF

  • TBD binds to TATA box

• TFIIA: joins complex

• TFIIB: binds DNA to TBP

• TFIIF: RNA Pol II joins complex by binding to TFIIB

• TFIIH: has helicase, unwinds DNA to make open complex & has kinase to phosphorylate Pol II at CTD (starts transcription)