MolecularCellBiology5068InClassExam1
September29,2015
ExamNumber:___________
Pleaseprintyourname:______________________________________
Instructions:
Pleasewriteonlyonthesepages,inthespacesallottedandnotontheback.Writeyournumberoneach
page(notyourname),sothatwecansplitthemupandgradethemanonymously.Thereareatotalof8
pagesincludingthiscoverpage.Youmaynotuseanybooksornotes,andnoelectronicaids,including
calculators.
Answeronlyinthespaceprovided;short,conciseanswersarepreferredandwillberewarded.Pleasebe
asneataspossible.
Whenyouarefinished,turnthisintotheTAandpickupthetake-homeportion.
Exam Number:______
MCB5068Exam1September29,2015
Dr.Mueckler’sLectures(30Points)
1.List2majorfunctionsoftheplasmamembraneincells.[2points]
2.Whatpropertyofphospholipidsmakesitthermodynamicallyfavorabletoformabilayer?Whyisthe
formationofasealedcompartmentbythisphospholipidbilayerenergeticallyfavorable?[2points]
3.Name2waysthatphospholipidsareinvolvedinsignaltransduction.[2points]
4.Explainthedifferencebetweenthescramblaseandflippaseenzymesbaseduponthemembraneswith
whichtheyareassociated,thesymmetryofthesemembranes,andtheirenergyrequirements.[4points]
-1-
5.Listthestepsinvolvedinsignal-mediatedtargetingofproteinstotheroughER.Besuretoincludeall
componentsinvolved.[6points]
6.Baseduponthechargedifferencerule,drawtheexpectedtopologyofthefollowingtransmembrane
protein.[2points]
7.Whatproteinisresponsiblefortheformationofdisulfidebonds?Wheredoesthisoccur?[2points]
-2-
Exam Number:______
8.Whatarethetwotransloconsresponsibleforimportingproteinsintothematrixofthemitochondria?
Doestheproteintraversethesetransloconsinafoldedorunfoldedstate?(3points)
9.Describeoneofthethreeroutesaproteinmaytravelinordertobeinsertedintotheinnermembrane
ofthemitochondria.Makesuretomentionallthecomponentsnecessary.[3points]
10.DescribehowtheRan-GDP/GTPconcentrationgradientisestablishedinordertoconfer
directionalityonnucleartransportbythekeryopherins.Makesuretomentionallthecomponents
necessaryforthiscycletooccur,includingthelocationsofRan-GAPandRan-GEF.[4points]
-3-
-4-
Exam Number:______
Dr.Hanson’sLectures(30Points)
1.Trueorfalse.Iffalse,pleasecorrect:thesmoothERisinvolvedinlipidmetabolismandsodium
sequestration/release.(1point)
2.WhattypeofcoatproteinsmarktransitionalER,alsoknownasERexitsites_____________________________.
(1point)
3. Briefly explain how chaperone proteins interact with nascent proteins in the ER. Is this an active or passive
process?(4points)
4.TheoligosaccharidethatisaddedenbloctonascentproteinsduringERfoldingiscomposedofa
particularpatternofsugarresidues.Pleaseexplainhowthisoligosaccharideismodifiedwhenanearly
foldedglycoproteinintermediaterequiresanotherroundthroughtheCalnexin/Calreticulincycle.(2
points)
-5-
5.BrieflyexplainthestrategyemployedbySchekmanetal.toscreenforandisolateyeastmutantswith
defectsinsecretion.(4points)
6.SomemembersoftheClostridiumgenusofbacteriahaveevolvedtoxinsthatcancauseparalysisin
animals(likehumans).Usingyourknowledgethatmembranetraffickingplaysanimportantroleinthe
functionofnerveterminalsliketheneuromuscularjunction,pleaseexplainhowthesetoxinscause
paralysis.(2points)
7.NEMsensitivefactor(NSF)formsacomplexwithSNAPandSNAREproteins.WhatistheroleofNSFin
membranetrafficking?(2points)
-6-
Exam Number:______
8.Trueorfalse;iffalse,pleasecorrect:synaptotagministhecalciumsensingproteinresponsiblefor
vesiclefusionwiththeplasmamembrane,asinthecaseofsynapticvesiclesandtheaxonterminal
plasmamembrane.(1point)
9.WhatreceptorisresponsiblefortheretrograderecyclingofERresidentproteinsfromtheGolgitothe
ER?Inyourresponse,pleasebesuretoincludethenameofthecoatproteinthisreceptorbindstoaswell
asthesequenceofthemotifitrecognizesonERresidentproteins(eithertheyeastorhighereukaryote
sequencewillsuffice).(3points)
10.Brieflydescribehownewlysynthesizedenzymesaretargetedtolysosomes.Inyourresponse,please
besuretomention:thesortingsignal,whereisthesignalreceptorlocated,i.e.whereisthesortingsignal
recognized,andthetraffickingcoatsystemutilized?(4points)
11.Trueorfalse;iffalse,pleasecorrect:theRabfamilyofproteinsarekeydeterminantsfordetermining
organelleidentity.(1point)
12.Trueorfalse.Iffalse,pleasecorrect:Membranetraffickingrequiresthattransportintermediates
undergofissionfromthedonorcompartmentandfusionwiththetargetcompartmentinahighly
regulatedseriesofmolecularreactions.(1point)
-7-
13.AnswereitherAorB.(4points)
A. How does intravesicular / lumenal pH change through the endocytic pathway? Briefly describe why this
is important for receptor recycling during endocytosis.
B. Of the LDL, Transferrin, and EGF receptor trafficking pathways discussed in class, choose your favorite
and briefly outline its itinerary through the endocytic pathway. Please be sure to comment on the fate of
the receptor and cargo.
Drs.Greenberg, Mahjoub, and MorleyLectures(35Points)
1.Name two potential in vivo functions of intermediate filaments, then highlight how your favorite
intermediate filament fulfills one of these functions. (3points)
2.Please list two ways in which intermediate filaments are unique from actin and microtubule filaments. (2
points)
-8-
Exam Number:______
3.Pleaselistthreeadvantagesofassemblingfilamentsfromsmallproteinsubunits.(3points)
4.Directionalityofpolymerizationoccursin2ofthe3filamenttypesdiscussedinclass.Brieflyoutline
themechanismofthedirectionality.Pleasebesuretocommentonhowthismechanismimpactsthe
relativecriticalconcentrationsofeitherendofthefilament.(2points)
5.Trueorfalse;iffalsepleasecorrect:The“treadmilling”ofafilamentrequiresnetadditionatoneend
andnetlossattheotherend.(1point)
6.Whichmicrotubulemotorproteindiscussedinclassisresponsibleforthemotilityofmotilecilium.[1
point]
7.Trueorfalse;iffalsepleasecorrect:ForminsareRho-GTPaseeffectorproteinsthatfunctionas
nucleatorsduringactinpolymerization.[1point]
-9-
8.Contrastactinandmicrotubulefilamentsintermsofsubunits,nucleotideenergysource,andthe
amountofelasticenergystoredwithinthefilament.Answersintheformofatablearepreferred.(3
points)
9.Cancersarecharacterizedbyuncontrolledcelldivision.Paclitaxelisataxolchemotherapeuticdrug
usedtotreatavarietyofcancers.Itsmechanismofactionisthestabilizationofmicrotubules.Usingyour
knowledgeofthemicrotubulefilamentkineticsandtheroleofmicrotubulesinthecell,pleasespeculate
astowhytaxolscanbeusedtotreatcancers.(2points)
10.Pleaselistthetwomicrotubulemotorproteinsdiscussedinclassandthedirectiontheymovealong
microtubules.Aretheseactiveorpassiveprocesses?Ifactive,whatnucleotideisutilized?(4points)
-10-
Exam Number:______
11.Microtubulesplaydiverserolesincells.Listthreewaysinwhichtheheterogeneityofmicrotubule
functionisregulated.[3points]
12.PleasenametwofunctionsoftheproteinProfilinintherapidremodelingoftheactincytoskeleton.[2
points]
13._________________________istheprimarycontractileelementinallmusclesandistheonlyknownmotor
proteintoactonactinfilaments.Mostproteinsinthissuperfamilyprocessivelymovetowardsthe_______
endofthefilament. [2points]
-11-
14.AnswereitherAorB.(2points)
A. NameyourfavoriteRas-relatedsmallGTP-bindingproteininvolvedwithactincytoskeletal
remodelingandbrieflydescribearoleforsubcellularstructureitforms.
B. Rigormortisisoneoftherecognizablesignsofdeathinwhichthemusclesofthebodyare
stiffened.Onacellularlevel,deathischaracterizedbytheinabilitytoreplenishdepleted
intracellularATPstores.Usingyourknowledgeofthepowerstrokeprocessthatoccursbetween
actinandtheprimarycontractileelementinallmuscles,pleasebrieflyexplainwhyrigormortis
occurs.
BonusQuestion:
15.CanadaistheUSA’slargestsingle-countrytradingpartner.WhatisthecapitalofCanada?(1point)
A. Ottawa
B. Montreal
C. Toronto
D. Vancouver
-12-
Exam Number:______
16.AnswereitherA,BorC.(4points)
A. Cellmotilityisdependentontherapidremodelingoftheactincytoskeleton.Chooseeitherthe
leadingortrailingedgeofthemovingcellandbrieflylist:thetypeofactinstructureinvolved,the
directionoftheactinfilaments(parallel,anti-parallel,orbranched)aswellasoneproteinthatis
importantforthisprocess.
B. BrieflydescribehowRas-relatedproteinscanbeactivatedorinactivated.Besuretomentionthe
roleofthetwoproteinsinvolvedinthisprocess.
C. InWiskottAldrichSyndrome,thebody’slymphocytes(defensecells)exhibitabnormalmotility.
TheWiskottAldrichSyndromeprotein(WASP)isinvolvedincellmotilitythroughinteractions
withaRas-relatedsmallGTPbindingproteinandaproteininvolvedintherapidremodelingofthe
actincytoskeleton.Pleaselistthesetwoproteinsandbrieflystatehowtheyfunctionin
conjunctionwithWASPtopromotecellmotility.
BonusQuestion:
16.Hypertrophiccardiomyopathy(HCM)istheleadingcauseofsuddendeathinpeople<35yearsof
age.Variantsin____________________________filamentsareassociatedwiththisdisease.(1point)
-13-