BIO 202 Study Guide - Midterm Guide: Lac Operon, Anabolism, Camp Concentration

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Chapter(18:(Regulation(of(Gene(Expression(
Part(One:(Prokaryotes(
1.#Describe#a#typical#bacterial#operon,#including#the#definition#of#Promoter,#Operator,#Repressor,#Co#repressor,#
and#Inducer.##
>##Bacterial#operons#are#bacterial#genetic#regulation#systems.#All#operons#consist#of#three#elements:#
!(genes(that(it(controls:(genes#coding#for#the#enzymes#of#a#particular#pathway#are#often#clustered#
together#and#transcribed#as#a#single#long#mRNA#molecule#
!#promoter(where(RNA(polymerase(binds:((a#single#promoter#regulates#the#synthesis#of#one#
polycistronic#mRNA.#
!##an(operator:(where#the#repressor#binds,#acts#as#an#“on>off#switch”,#lies#between#the#promoter#and#
the#first#gene.#Operons#allow#coordinated#regulation#of#related#gene#products.#
#####*#The#promoter#and#operator#are#overlapping#DNA#sequences,#so,#like#musical#chairs,#only#one#can#be#
present#at#a#time.#If#a#repressor#binds#to#an#operator,#RNA#polymerase#cannot#bind.##
#
#
2.#Describe#a#repressible#operon#and#an#inducible#operon,#and#explain#why#both#can#be#examples#of#negative#
control.#
#
>#Negative#control:#repressor#has#the#ability#to#repress#
expression#of#the#operon#
>(Inducible(Operon:#Transcription#is#usually#off#but#can#
be#induced#(activated)#by#an#inducer.#
#Uses(Inducible(Enzymes:#Usually#used#in#catabolic#
pathways#which#break#down#material#
Ex:#Lac#operon:#Synthesizes#enzymes#that#break#
down#allolactose.##
#
>#Repressible(operon:#Transcription#is#usually#on#but#
can#be#repressed#using#co>repressor.#
Uses(Repressible(Enzymes:#Used#in#anabolic#pathways#
(pathways#that#use#energy#to#synthesize#products#from#
raw#materials.##
Ex:#Trp#operon:#An#anabolic#pathway#that#codes#
for#the#creation#of#the#amino#acid#tryptophan.#Trp#
concentrations#high#!#some#bind#to#repressor#!#make#
it#active#!#interfere#w/#transcription#
#
#
#
#
#
#
#
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3.#Describe#the#role#of#cAMP#in#the#regulation#of#the#lac#operon.#
>#The#absence#of#glucose#activates#the#expression#of#the#lac#operon#through#positive#control.##
>#When#glucose#concentration#in#cells#are#high,#cAMP#levels#are#low,#but#when#glucose#concentration#is#low#
cAMP#concentration#is#high.#A#protein#called#CAP#is#activated#by#cAMP,#and#when#activated,#it#binds#to#the#
promotor#region#of#the#lac#operon,#encouraging#transcription#in#the#presence#of#lactose.#Overall(this(means(
that(the(presence(of(cAMP(signifies(low(levels(of(glucose(in(the(cell,(which(prompts(digestion(of(lactose(
instead.((
>#Elevated#levels#of#cAMP#(glucose#levels#are#low)#!#cAMP#activated#a#protein#CAP#(catabolic#activator#protein)#
that#gets#behind#RNA#at#the#lac#operon#and#gives#it#a#good#hard#kick.##
*#Highest#lac#expression:#glucose#levels#low,#lactose#levels#high.##
#
Part(Two:(Eukaryotes(
1.#Describe#the#structure#of#chromatin#and#the#difference#between#heterochromatin#from#euchromatin.#
>#Chromatin#structure:#“beads#on#a#string”#DNA#is#wrapped#around#(+#charged)#histones.#They#are#oriented#in#a#
way#such#that#their#expressed#euchromatic#regions#are#towards#the#middle#of#the#nucleus.##
>#Interphase#chromosomes#have#highly#condensed#areas,#called#heterochromatin,#and#less#compacted#areas,#
called#euchromatin.#
>#heterochromatic(regions#are#usually#structural#regions#of#the#chromosomes#(ex:+regions+w/+no+genes,+like+
telomeres+and+centromeres#!#provide+structure+to+the+chromosome)#and#genes#that#are#silenced#in#that#cell#
type#as#cells#assume#their#fate#(ex:+lung,+liver,+kidney+cells).#They#are#usually(not(expressed#because#RNA#
polymerase#needs#to#be#able#to#find#the#promoter#region,#etc.##
#
#
2.#Recall#the#structure#and#function#of#the#histone#proteins,#the#chemical#interaction#between#histone#proteins#
and#DNA,#and#the#structure#of#the#nucleosome.#
>#Histone(proteins#are#positively#charged#that#DNA#which#is#
negatively#charges#wraps#around#to#condensify.##
>#Nucleosome:#8#histone#protein#bead#structures##
#
3.#Describe#the#influences#of#acetylation#and#methylation#on#
eukaryotic#DNA#transcription.#
>#DNA(Methylation:(“Silencing#gene#method”#reduced#
transcription#in#vertebrates.#Addition#of#methyl#group#to#
nucleotides.#This#turns#off#a#gene#permanently.#RNA#polymerase#
cannot#transcribe#this#gene.#This#happens#to#stem#cells#when#a#
child#is#being#created.#Methylated#DNA#+#deacetylated#histones#
are#found#together#!#silenced#gene.##
>#Histone(Acetylation:(Increases#transcription#rate.#An#acetyl#
group#is#added#to#lysine#amino#acid.#This#causes#the#DNA#
wrapped#around#histones#to#be#loosened#because#histones#lose#
their#(+)#charge.##
>#Histone(Deacetylation:(Decreases#transcription#rate.(And#acetyl#group#is#removed#from#lysine#amino#acid#
which#causes#DNA#around#the#histones#to#tighten.##
#
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4.#List#the#post>transcriptional#modifications#during#eukaryotic#mRNA#processing.#
>#Alternative#splicing#&#mRNA#degradation#
#
5.#Describe#the#process#and#significance#of#alternative#splicing.##
>#Alternative(splicing#allows#more#than#one#protein#to#be#generated#from#a#single#transcription#unit.#This#
results#in#inclusion#or#elimination#of#specifics#introns#or#exons#!#variation#in#amino#acid#sequence.##
#
6.#Understand#regulation#of#gene#expression#at#the#level#of#mRNA#stability#and#translation#initiation.#
>#mRNA#has#a#very#short#life#span#because#it#is#sensitive#to#hydrolysis,#etc.#You#can#stabilize#them#so#they#don’t#
disappear#as#rapidly.#The#sequence#from#the#untranslated#regions#(UTR)#upstream#and#downstream#of#the#
coding#sequence#and#the#proteins#that#bind#to#UTRs#either#protect#it#from#nucleases#or#allow#for#degradation#
!#mRNA(life(span(is(determined(in(part(by(sequences(in(the(5’(and(3’(UTRs.((
>#Initiation(of(translation#of#selected#mRNAs#can#be#blocked#by#regulatory#proteins#that#bind#to#sequences#or#
structures#of#the#mRNA,#translation#of#all#mRNAs#in#a#cell#may#be#regulated#simultaneously#(ex:+translation+
initiation+factors+are+simultaneously+activated+in+an+egg+following+fertilization)#
#####!#RNA#can#be#folded#on#itself#in#such#a#way#that#the#start#codon#is#not#visible#!#ribosome#will#not#see#it#!#
no#translation#(RNA’s#are#blocked#from#being#translated)##
#
7.#Understand#the#role#of#ubiquitin#and#the#proteasome.#
>#Ubiquitin#is#a#tiny#peptide#that#binds#to#a#protein#to#signal#proteasome#to#attack#it.#Proteasomes#are#giant#
protein#complexes#that#bind#protein#molecules#and#degrade#them.##
#
8.#Explain#how#differentiation#produces#multiple#cell#types.##
>#Cytoplasmic#determinants(are#maternal#substances#(RNA,#
proteins)#in#the#egg#that#influence#early#development.#If#they#are#
unevenly#distributed#in#the#egg#cytoplasm,#daughter#cells#will#
contain#different#cytoplasmic#determinants,#which#can#lead#to#
different#gene#expression#and#differentiation.#
>#Induction:#one#cell#releases#signaling#molecules#that#tell#another#
cell#how#to#proceed.#(paracrine#signaling#!#mosquito#bites#&#how#
they#swell)#
#
#
#
#
9.#Describe#how#changes#in#gene#expression#control#differentiation.##
>#Cell#differentiation#is#marked#by#the#production#of#tissue>specific#genes#(ex:+when+cells+are+determined+to+be+
muscle+cells,+they+start+to+express+MyoD+which+turns+on+the+expression+of+other+transcription+factors+that+turn+
the+cell+into+a+muscle+cell)#
#
10.#Relate#factors#that#determine#gene#expression#during#differentiation#and#morphogenesis.##
#
11.#Understand#what#is#meant#by#positional#information,#pattern#formation,#cytoplasmic#determinants,#
morphogens,#maternal#effect#genes,#homeotic#genes.##
>#Pattern(formation:#development#of#spatial#organization#of#tissues#and#organs#(setting#up#a#body#plan,#
conserved#in#the#animal#kingdom).#Begins#with#the#establishment#of#major#axes.##
>#Positional(information:#molecular#cues#that#control#pattern#formation,#tells#a#cell#its#location#relative#to#the#
body#axes#and#to#neighboring#cells#(GPS);#how#a#cell#knows#where#in#the#body#there#are##
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