BIOL 142 Chapter Notes - Chapter 19.1: Chromatin Remodeling, Chromatin, Euchromatin
30 Apr 2018
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19.1$Gene$Regulation$in$Eukaryotes$–$An$Overview$
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Differential*gene*expression:!expression!of!different!sets!of!genes!in!cells!with!the!same!genome;!
responsible!for!creating!different!cell!types!
• Bacteria!regulate!gene!expression!to!respond!to!change!in!their!environment!
• In!multicellular!eukaryotes,!variations!in!gene!expression!is!more!pronounced!because!the!cells!
respond!to!changes!in!the!organism's!internal!environment!
o Cells!with!the!same!genome!express!different!sets!of!genes!through!differential*gene*
expression!that!arranges!the!cells!into!the!right!places!and!coordinates!their!activity!
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Additional!levels!of!control:!
• Chromatin*remodeling!occurs!before!transcription!
o Chromatin*remodeling:!the!process!by!which!the!structure!of!chromatin!is!changed!to!allow!
or!inhibit!transcription!or!replication;!may!involve!chemical!modification!of!histone!proteins!
or!reshaping!of!the!chromatin!by!large!multiprotein!complexes!in!an!ATP-requiring!process!
o DNA!is!wrapped!around!proteins!to!create!chromatin:!the!complex!of!DNA!and!proteins,!
mainly!histones,!that!compose!eukaryotic!chromosomes!
• Heterochromatin!–!highly!compact!
• Euchromatin!–!loosely!coiled!
o Before*transcription*can*begin,*the*stretch*of*DNA*containing*the*promotor*must*be*
released*from*the*tighter*interactions*with*proteins*so*that*RNA*polymerase*can*make*
contact*with*the*promoter!
• RNA*processing:!in!eukaryotes,!the!changes!that!a!primary!RNA!transcript!undergoes!to!become!a!
mature!RNA!molecule;!the!steps!required!to!produce!mature,!processed!mRNA!from!a!primary!
RNA!transcript!
o For!pre-mRNA!it!includes!the!addition!of!a!5'!cap!and!a!poly(A)!tail!and!splicing!to!remove!
introns!
o If!different!cells!use!different!splicing!patterns,!different!gene!products!result!
• mRNA!stability!–!mRNAs!that!remain!the!cell!for!a!long!time!tend!to!be!translated!more!than!
mRNA!that!have!a!short!life!span!
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In!eukaryotes,!gene!expression!can!be!controlled!at!many!different!levels!
• Like!bacteria,!eukaryotes!can!control!gene!expression!at!the!levels!of!transcription,!translation,!
and!post-translation!
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