ch 18 reading guide- answers

7/26/2019 Ch 18 Reading Guide- Answers

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AP Biology Reading Guide Fred and Theresa Holtzclaw Copyright 200 Pearson !ducation

Name___________________________________ Date___________________ Period_______

Chapter 18: Regulation of Gene ExpressionOverview

The o"er"iew #or Chapter $ introduces the idea that while all cells o# an organis% ha"e all genes in the

geno%e& not all genes are e'pressed in e"ery cell( )hat regulates gene e'pression* Gene e'pression inpro+aryotic cells di##ers #ro% that in eu+aryotic cells( How do disruptions in gene regulation lead to

cancer* This chapter gi"es you a loo+ at how genes are e'pressed and %odulated(

Concept 18.1 Bacteria often respond to environmental change by regulating transcription

( All genes are not ,on- all the ti%e( .sing the %eta/olic needs o#E. coli& e'plain why not(!( coli wor+s /y acti"ating a %eta/olic pathway that %a+es tryptophan( This only happens when the

hu%an does not eat any %eat( nce %eat is eaten& !( coli stops to sa"e its energy #or when the %eat

is gone(

2( )hat are the two %ain ways o# controlling %eta/olis% in /acterial cells*

Cells can ad1ust the acti"ity o# enzy%es already present with che%ical cues through #eed/ac+

inhi/ition

Cells can ad1ust the production le"el o# the genes encoding the enzy%es

(Feedback inhibition is a recurring %echanis% throughout /iological syste%s( 3n the case o#E. coli

regulating tryptophan synthesis& is itpositive or negative inhibition* !'plain your choice(

3t is negati"e inhi/ition /ecause the accu%ulation o# the product stops the enzy%e #ro% catalyzing it(

4( )hat is apromoter*A pro%oter is a se5uence o# 67A nucleotides where R7A poly%erase /inds to in order to start

transcription(

8( )hat is the operator* )hat does it do*An operator is a se5uence o# nucleotides near the start o# an operon where an acti"e repressor can attach(

3t pre"ents R7A poly%erase #ro% attaching to the pro%oter and transcri/ing the genes o# the operon(

9( )hat is an operon*

An operon is a unit o# genetic #unction #ound in /acteria and phages( 3t includes a pro%oter& anoperator& and the genes they control(

:( ;ist the three co%ponents o# an operon& and e'plain the role o# each one(

Pro%oter< starts transcription

perator< n=## switch< synthesizes enzy%es at once

Genes they control< deter%ines whether or not a certain a%ino acid will /e coded #or

$( How does a repressorprotein wor+*

A repressor protein /inds to the operator and /loc+s the attach%ent o# R7A poly%erase tot the

pro%oter& which pre"ents transcription o# a gene(

>( )hat are regulatory genes*Regulatory genes code #or a protein that controls the transcription o# another gene or group o#

genes(0( 6istinguish /etween inducible and repressible operons& and descri/e one e'a%ple o# each type(

Repressi/le operons are usually on /ut can /e inhi/ited when a speci#ic s%all %olecule /inds

allosterically to a regulatory protein( ?e'@ tryptophan operon

An induci/le operon is usually o## /ut can /e sti%ulated when a speci#ic s%all %olecule interacts

with regulatory proteins( ?e'@ lactose operon

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( ;a/el this s+etch o# the lac operon with the ter%s at right( now the #unction o# each structure(

Operon genes

Operon

RNA polymerase

mRNA

Repressor protein

Operator

Repressor

Regulatory geneInducer

2( Co%pare and contrast the lac operon and the trp operon( ?Re%e%/er that compare %eans ,to tell how

they are si%ilar&- and contrast %eans ,to tell how they are di##erent(-

Both operons code #or an allosteric repressor protein that can switch on and o##( The trp operon is

inacti"e /y itsel# and re5uires tryptophan as a co%pressor( The lac operon is acti"e /y itsel#(

( )hat happens when a repressor is /ound to the operator*

The gene is not transcri/ed /ecause the R7A poly%erase cannot /ind( ?the operon is o##

4( )hat is CAP* How does CAP wor+*

CAP is Cata/olic Acti"ator Protein( This is a regulatory protein that /inds to 67A and sti%ulates

transcription o# a gene(

8( !'plain why CAP /inding and sti%ulation o# gene e'pression ispositive regulation(

CAP /inding increases the rate o# transcription ?gene e'pression& which is a positi"e regulation /ecause

it is perpetually increasing(

9( 6escri/e the relationship /etween glucose supply& cAP& and CAP(

cAP is attached to the regulatory protein( )hen the a%ount o# glucose in a cell increases& cAP

concentration lowers& CAP detaches #ro% the operon /ecause there isnDt enough cAP to hold it(

:( How can /oth repressi/le and induci/le operons /e negative regulators*

Their products inhi/it the production o# %ore products& %a+ing the% negati"e regulators(

Concept 18.2 Eukaryotic gene epression can be regulated at any stage

$( !"en though all cells o# an organis% ha"e the sa%e genes& there is dierential gene e!pression( )hat

does this %ean*The e'pression o# di##erent genes /y cells with the sa%e geno%e are showing(

>( )hat percentage o# the genes o# a typical hu%an cell is e'pressed at any gi"en ti%e* 20E

20( )hat is the co%%on control point o# gene e'pression #or all organis%s*

Transcription

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2( Gene e'pression can /e regulated /y %odi#ications o# the chro%atin( 6istinguish /etween

heterochromatin and euchromatin as to their structure and acti"ity(

Heterochro%atin is highly condensed and rarely e'pressed( !uchro%atin ?,true chro%atin- is lightly

condensed and help regulate gene e'pression(

22( )hat occurs in histone acetylation* How does it a##ect gene e'pression*

Acetyl groups are attached to lysines in histone tails( This pro%otes transcription initiation /y gi"ing

proteins easier access to the genes(

2( )hat is"NA methylation* )hat role %ay it play in gene e'pression*

Addition o# a %ethyl group on the 67A /ases o# eu+aryotes %a+es cells hea"ier and turns o## genes(

24( The inacti"e %a%%alian chro%oso%e is hea"ily %ethylated( )hat is the result o# this %ethylation*

28( )hat isgenomic imprinting& and how is it %aintained* Gi"e an e'a%ple discussed earlier in hu%an

genetics(

29( !'plain what is %eant /y epigenetic inheritance& and gi"e an e'a%ple o# epigenetic changes

discussed in the te't or in class(

2:( .se the s+etch /elow to e'plain how enhancers and acti"ators interact with transcription #actors to

a##ect gene e'pression( ;a/el the #ollowing ele%ents@ #A#A bo!$ promoter$ gene$ enhancer$

activators$ transcription actors$ transcription initiation comple!$ RNA polymerase II$ and"NA.Then place your e'planation to the right o# the #igure(

EXPLN!"#N

2$( 3n pro+aryotes& #unctionally related genes are usually clustered in a single operon( )hat has /een

#ound to /e the case in eu+aryotes*

2>( perons ha"e not /een #ound in eu+aryotic cells& and the genes coding #or the enzy%es o# a particular

%eta/olic pathway are o#ten scattered o"er di##erent chro%oso%es( )hat is a plausi/le %echanis%

#or the coordination o gene e!pression*

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0( How can alternative RNA splicing result in di##erent proteins deri"ed #ro% the sa%e initial R7A

transcript*

(Posttranscriptional control includes regulation o# mRNA degradation( !'plain how this a##ectstranslation(

2( How can proteins /e acti"ated& processed& and degraded* Gi"e an e'a%ple or descri/e each process(

( An article in %cientiic American a/outproteasomes was entitled ,;ittle Cha%/er o# Horrors(-

!'plain how proteins are targeted #or degradation& and gi"e a speci#ic e'a%ple o# when this %ight

occur(

4( How do these ,little cha%/ers o# horrors- #unction* Annotate the s+etch /elow to descri/e their

action( Then e'plain their role in regulation o# gene e'pression(

Concept 18.! "oncoding #"$s play multiple roles in controlling gene epression

8( 3t is now +nown that %uch o# the R7A that is transcri/ed is not translated into protein( these R7Asare called noncoding RNAs( Read care#ully to discern a crucial role played /y these R7As( )hat is this

role*

9( ne o# the noncoding RNAs that regulate gene e'pression is microRNA( n the s+etch /elow& #ollow

an R7A loop& called a ,hairpin&- #ro% its creation( !'plain the two %odes o# action o# microRNAs(

Be sure to la/el the location o# hydrogen /onds and"icer(

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Concept 18.% $ program of differential gene epression leads to the different cell types in a

multicellular organism

This concept deals with the regulation o# gene e'pression in de"elop%ent( Ani%al de"elop%ent is also

discussed in Chapter 4:(

:( )hat three processes lead to the trans#or%ation o# a zygote into the organis%*

$( !'plain what occurs in cell dierentiation and morphogenesis(

>( 6i##erential gene e'pression results #ro% di##erent acti"ators in di##erent cells( How do di##erent sets

o# acti"ators co%e to /e present in two cells* !'plain how each o# these occurs@

a( distri/ution o# cytoplasmic determinants

/( di##erent inductive signals

40( )hat is %eant /y determination* !'plain what this %eans within an e%/ryonic cell(

4( )hat process ensures that all the tissues and organs o# an organis% are in their characteristic places*

)here do the %olecular cues that control this process arise*

42( )hat is controlled /y homeotic genes*

Concept 18.& Cancer results from genetic changes that affect cell cycle control

4( )hat %echanis% is in"ol"ed in the /eginning o# tu%or growth* 6iscuss oncogenes and proto&oncogenes(

44( )hat are three %echanis%s #or con"erting a proto


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48( There see% to /e two categories o# genes in"ol"ed in cancer@ oncogenes& which code #or proteins to

regulate cell growth& and should not /e stuc+ ,on&- %uch li+e the accelerator in a car and tumor&

suppressor genes& which wor+ li+e the /ra+es on a car and %ust #unction ;etDs /egin with a loo+ at the

ras gene& which codes #or a G protein and is an oncogene( ;a/el the s+etch /elow to e'plain how a ras

%utation leads to cancer(

49( #umor&suppressor genes help pre"ent uncontrolled cell growth( ne that is #ound %utated ?and

there#ore non#unctional in %ore than 80E o# hu%an cancer isp'(( Io i%portant is thep'( gene that it is

so%eti%es called the ,guardian angel o# the geno%e(- 6escri/e the dou/le wha%%y that results #ro%

%utation o#p'((

4:( !'plain the multistep model o cancer development/y using the speci#ic e'a%ple o# colorectal cancer(

The #igure /elow %ay /e la/eled to help in your e'planation(

#esting )our *nderstanding+ %el&,ui- Ansers

7ow you should /e ready to test your +nowledge( Place your answers here@(JJJJJJJ 2(JJJJJJJ (JJJJJJJJ 4(JJJJJJJJ 8(JJJJJJJJ 9(JJJJJJJJ :(JJJJJJJJ $(JJJJJJJJ >(JJJJJJJJ 0(JJJJJJJJ

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ch 18 reading guide- answers

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