IntroductionotooEssentialsoofoCelloBiologyo|oLearnoScienceoatoScitable Pageo1oofo1
Essentials of Cell Biology
o o o
Whatodooanoamoebaoandoanoelephantohaveoinocommon?oIfoliverocellsohaveotheosameoDNAoasobrainocells,owhyoareotheyo d
ifferent?oWhatogoesowrongoduringocancer?oTheoanswersotootheseoquestionsodependoonotheopropertiesoofocells,otheofundament
alo unitsoofolife.oEssentialsoofoCelloBiologyointroducesoreadersotootheocoreoconceptsoofocellobiology.oThisocourseocanoprovi
deoano introductionotoocellobiologyoforobeginningostudentsoofoalloagesoorobeoaospringboardotoomoreospecializedotopicsoforoa
dvancedo students.oTheocourseobeginsowithoaodiscussionoofotheofundamentalopropertiesoofocells:otheooriginoofotheocell,ohow
ocellsoareo organized,ohowotheyoreproduce, oandohowotheyouseoenergy.oOtherounitsoinotheocourse oexpandotheseotopicsoandop
rovideoinsighto intootheoprocessesothatoregulateocellofunctionoandogenerateotheoamazingovarietyoofocellotypesoseenoinolivingo
organisms.oTopicso includeotheodecodingoprocessothatoproducesodistinctosetsoofoproteinsoinodifferentocellotypes,otheocellular
ostructuresoresponsible o forocellofunction, otheosignalsothat ocellsouseotoocommunicate owithooneoanother,oandotheointricate ocont
rolsoonocellodivision.oAtotheo endoofoeachounitoinothisoeBookothereoisotheooptionotootestoyouroknowledgeowithotwentyomulti
ple-choiceoquestions.
AboutotheoAuthors
LeadoEditor:oClareoO'Connor,oPh.
D.o Writer:oJilloU.oAdams,oPh.D.
Illustrations:o Jennifero E.o Fairman,o C.M.I.,o F.A.M.I.
ClareoO’ConnoroisoanoAssociateoProfessoroinotheoBiologyoDepartmentoatoBostonoCollege.oSheoteachesocoursesoinocellobio
logyo andogenetics.oSheohasorecentlyodevelopedonewolaboclassesothatoengageostudents oinofunctionalogenomicsoresearch.oCl
areospendso aolotoofotimeothinkingoaboutohowotoouseoelectronicolearningoresourcesotoogetostudentsoexcitedoaboutoscience.
JilloU.oAdams oisoaoscientist-turned-science-
writerowhoowritesoaboutohealth,omedicine,oandoscientificoresearchoforoscientistsoando layoaudiencesoalike.oSheogotohookedoon
ocellobiologyowell oafterograduate oschool, othroughoreadingoLewisoThomasoandowritingo aboutocellularoprocessesosuchoasoauto
phagy,otheocell'soultimateoformooforecycling.
JenniferoFairmanoisotheoFounderoandoPrincipaloofoFairmanoStudios,oLLC.oSheoalsooholdsoa ofacultyoappointmentoasoAssi
stanto ProfessoroinotheoDepartmentoofoArtoasoAppliedotooMedicineoatoJohnsoHopkinsoUniversityoSchooloofoMedicine.oJenn
iferoenjoyso translatingoscienceointooimagesothatopeopleocanoeasilyounderstand.
Citation
Pleaseociteothisobookoas:
O'Connor,oC.oM.o&oAdams,oJ.oU.oEssentialsoofoCelloBiology.oCambridge,oMA:oNPGoEducation,o2010.
http://www.nature.com/scitable/ebooks/essentials-of-cell-biology-14749010 8/9/2011
,EssentialsoofoCelloBiologyo|oLearnoScienceoatoScitable Pageo1oofo1
WhatoIsoaoCell?oWhatoAreotheoEssentialoCharacteristicsoofoCells
?
HowoDooCellsoDecodeoGeneticoInformationointooFunctionaloProteins?o
HowoAreoEukaryoticoCellsoOrganizedointooSmalleroParts?
HowoDooCellsoSenseoTheiroEnvironment?
How Do Cells Know When to Divide?
http://www.nature.com/scitable/ebooks/essentials-of-cell-biology-14749010/contents 8/9/2011
,Unito1oofoEssentialsoofoCelloBiologyo|oLearnoScienceoatoScitable Pageo1oofo2
EssentialsoofoCelloBiologyo o Contents
PROGRESS 20% 40% 60% 80% 100%
Prev Page
Unito1:o WhatoIsoaoCell?oWhatoAreotheoEssentialoCharacteristicsoofoCells? o
NextoPage
Whatoareotheseoliving ounitsocalledocells?oMucholikeomini-
fiefdoms,ocellsohaveoall otheoequipmentoandoexpertiseo necessaryotoocarryooutotheofunctionsoofolife.oAocelloca
noeat,ogrow,oandomove.oItocanoperformonecessaryo maintenance,orecycleoparts,oandodisposeoof owastes. oItocan
oadaptotoochanges oinoits oenvironment; oandoitocanoeveno replicate oitself.
Despiteotheseosimilarities,oallocellsoare onotoequal.oSome oare otrulyoself-sustaining,oasowithosingle-
celledobacteriao oroyeast,owhereasoothersoliveocommunally,osometimesoasopartoofocomplexomulticellularoorg
anisms.oCellsoalsoo differoinosize.oAlthoughocellsocanobeoquiteolargeo—
oconsideroaofrog'soegg,oforoexample o—
omost oareotooosmallotoo seeowithotheonaked oeye.oIndeed,otheodevelopment oofolight omicroscopyowasoessential o
tooman'sodiscoveryoofocells.
Don'tobeolulledobyofamiliaroschematicodrawingsoofooval-shapedocells,oeither.oRealocellsoareothree-
dimensional,oofo course,oandotheyoexistoinoaovarietyoofointricateoandoremarkableoshapes.oForoinstance,oaosin
gleohumanonerveocello canobeooverooneometerolong,oextendingofromoyourobackboneotooyourobigotoe.oComp
areothatowithotheocellsothato lineoyourosmallointestine, owhich ohave odozensoof otiny,ofingerlikeoprojections otoo
maximize otheosurfaceoareaoacrosso whichonutrientsocanopass.
Butohow,oexactly,odoocellsoaccomplishotheocomplexotasksoofolife?oWhatotoolsoandomaterialsodootheyoneed?oA
ndo whatoareotheokeyocharacteristicsothatodefineoaocell?oThisounitoanswersotheseoquestionsoandoprovidesoaob
asico overviewoofotheoinneroworkingsoofotheocell.
InoThisoUnit
CellsoAre otheoBasic oUnitsoofo L
ivingoOrganisms
EukaryoticoCellsoPossessoao N
ucleusoandoMembrane-
Boundo Organelles
CelloFunction oDependsoonoth
eo ContinualoUptakeoando C
onversionoofoEnergy
Photosynthetic oCellsoCaptureo
LightoEnergyoandoConvertoItoto
o Chemical oEnergy
MetabolismoisotheoCompleteoS
eto ofoBiochemicaloReactionso
withinoaoCell
Test oYouroKnowledge
http://www.nature.com/scitable/ebooks/essentials-of-cell-biology-14749010/what-is-a-cell-... 8/9/2011
, ContentsoofoEssentialsoofoCelloBiologyo|oLearnoScienceoatoScitable Pageo1oofo4
PROGRESS 20% 40% 60% 80% 100%
Treesoinoaoforest,ofishoinoaoriver,ohorsefliesoonoaofarm,olemursoinotheojungle,oreedsoinoaopond,owormsoinotheosoilo—
oallotheseo plantsoandoanimalsoareomadeoofotheobuildingoblocksoweocallocells.oLikeotheseoexamples,omanyolivingothings
oconsistoofovasto numbersoofocellsoworkingoinoconcertowithooneoanother.oOtheroformsoofolife,ohowever,oareomadeoofoonl
yoaosingleocell,osuchoaso theomanyospeciesoofobacteriaoandoprotozoa.oCells,owhetherolivingoonotheiroownooroasopartoofo
aomulticellularoorganism,oareo usuallyotooosmallotoobeoseenowithoutoaolightomicroscope.
Cellsoshareomanyocommonofeatures,oyetotheyocanolookowildlyodifferent.oInofact,ocellsohaveoadaptedooverobillionsoofoyear
sotooao wideoarrayoofoenvironmentsoandofunctionaloroles.oNerveocells,oforoexample,ohaveolong,othinoextensionsothatocano
reachoforo metersoandoserveotootransmitosignalsorapidly.oCloselyofitting,obrick-
shapedoplantocellsohaveoaorigidoouterolayerothatohelpso provideotheostructuralosupportothatotreesoandootheroplantsorequire.o
Long,otaperedomuscleocellsohaveoanointrinsicostretchinessothato allowsothemotoochangeolengthowithinocontractingoandorela
xingobiceps.
Still,oasodifferentoasotheseocellsoare,otheyoallorelyoonotheosameobasicostrategiesotookeepotheooutsideoout,oallowonecessary
o substancesoinoandopermitoothersotooleave, omaintainotheirohealth, oandoreplicateothemselves. oInofact, otheseotraitsoareoprecise
WhatoDefinesoaoCell?
Figureo1:oTransportoproteinsoinotheocellomembrane
Aoplasma omembraneoisopermeableotoospecificomolecules othatoaocellone
eds.o Transportoproteinsoinotheocellomembraneoallowoforoselectiveopass
ageoofo specificomoleculesofromotheoexternaloenvironment.oEachotranspo
rtoproteinoiso specificotooaocertainomoleculeo(indicatedobyomatchingocol
ors).
©o2010oNatureoEducationoAllorightsoreserved. o
Cellsoareoconsideredotheobasicounitsoofolifeoinopartobecauseotheyocomeoinodiscreteoandoeasilyorecognizableopackages.oT
hat'so becauseoallocellsoareosurroundedobyoaostructureocalledotheocellomembraneo—
owhich, omucholikeotheowallsoofoaohouse,oservesoaso aoclearoboundaryobetweenotheocell'sointernaloandoexternaloenvironme
nts.oTheocellomembraneoisosometimesoalsooreferredotooaso theoplasmaomembrane.
Cellomembranesoareobasedoonoaoframeworkoofofat-
basedomoleculesocalledophospholipids,owhichophysicallyopreventowater-
o loving,oorohydrophilic,osubstancesofromoenteringooroescapingotheocell.oTheseomembranesoareoalsoostuddedowithoprotein
sothato serveovariousofunctions.oSomeoofotheseoproteinsoactoasogatekeepers, odeterminingowhatosubstancesocanoandocannot
ocrossotheo membrane.oOthersofunctionoasomarkers,oidentifyingotheocelloasopartoofotheosameoorganismooroasoforeign.oStill
oothersoworkolikeo fasteners,obindingocellsotogetherosootheyocanofunctionoasoaounit.oYetootheromembraneoproteinsoserveoaso
communicators,osendingo andoreceivingosignalsofromoneighboringocellsoandotheoenvironmento—
owhetherofriendlyooroalarmingo(Figureo1).
Withinothisomembrane,oaocell'sointerioroenvironmentoisowaterobased.oCalledocytoplasm,othisoliquidoenvironmentoisopacke
dofullo ofocellularomachineryoandostructuraloelements.oInofact,otheoconcentrationsoofoproteinsoinsideoaocellofarooutnumber
othoseoonotheo outsideo—owhetherotheooutsideoisooceanowatero(asoinotheocaseoofoaosingle-
celledoalga)oorobloodoserumo(asoinotheocaseoofoaoredo bloodocell).oAlthoughocellomembranesoformonaturalobarriersoinow
ateryoenvironments,oaocellomustononethelessoexpendoquiteoa
http://www.nature.com/scitable/ebooks/essentials-of-cell-biology-14749010/16433178 8/9/2011
Essentials of Cell Biology
o o o
Whatodooanoamoebaoandoanoelephantohaveoinocommon?oIfoliverocellsohaveotheosameoDNAoasobrainocells,owhyoareotheyo d
ifferent?oWhatogoesowrongoduringocancer?oTheoanswersotootheseoquestionsodependoonotheopropertiesoofocells,otheofundament
alo unitsoofolife.oEssentialsoofoCelloBiologyointroducesoreadersotootheocoreoconceptsoofocellobiology.oThisocourseocanoprovi
deoano introductionotoocellobiologyoforobeginningostudentsoofoalloagesoorobeoaospringboardotoomoreospecializedotopicsoforoa
dvancedo students.oTheocourseobeginsowithoaodiscussionoofotheofundamentalopropertiesoofocells:otheooriginoofotheocell,ohow
ocellsoareo organized,ohowotheyoreproduce, oandohowotheyouseoenergy.oOtherounitsoinotheocourse oexpandotheseotopicsoandop
rovideoinsighto intootheoprocessesothatoregulateocellofunctionoandogenerateotheoamazingovarietyoofocellotypesoseenoinolivingo
organisms.oTopicso includeotheodecodingoprocessothatoproducesodistinctosetsoofoproteinsoinodifferentocellotypes,otheocellular
ostructuresoresponsible o forocellofunction, otheosignalsothat ocellsouseotoocommunicate owithooneoanother,oandotheointricate ocont
rolsoonocellodivision.oAtotheo endoofoeachounitoinothisoeBookothereoisotheooptionotootestoyouroknowledgeowithotwentyomulti
ple-choiceoquestions.
AboutotheoAuthors
LeadoEditor:oClareoO'Connor,oPh.
D.o Writer:oJilloU.oAdams,oPh.D.
Illustrations:o Jennifero E.o Fairman,o C.M.I.,o F.A.M.I.
ClareoO’ConnoroisoanoAssociateoProfessoroinotheoBiologyoDepartmentoatoBostonoCollege.oSheoteachesocoursesoinocellobio
logyo andogenetics.oSheohasorecentlyodevelopedonewolaboclassesothatoengageostudents oinofunctionalogenomicsoresearch.oCl
areospendso aolotoofotimeothinkingoaboutohowotoouseoelectronicolearningoresourcesotoogetostudentsoexcitedoaboutoscience.
JilloU.oAdams oisoaoscientist-turned-science-
writerowhoowritesoaboutohealth,omedicine,oandoscientificoresearchoforoscientistsoando layoaudiencesoalike.oSheogotohookedoon
ocellobiologyowell oafterograduate oschool, othroughoreadingoLewisoThomasoandowritingo aboutocellularoprocessesosuchoasoauto
phagy,otheocell'soultimateoformooforecycling.
JenniferoFairmanoisotheoFounderoandoPrincipaloofoFairmanoStudios,oLLC.oSheoalsooholdsoa ofacultyoappointmentoasoAssi
stanto ProfessoroinotheoDepartmentoofoArtoasoAppliedotooMedicineoatoJohnsoHopkinsoUniversityoSchooloofoMedicine.oJenn
iferoenjoyso translatingoscienceointooimagesothatopeopleocanoeasilyounderstand.
Citation
Pleaseociteothisobookoas:
O'Connor,oC.oM.o&oAdams,oJ.oU.oEssentialsoofoCelloBiology.oCambridge,oMA:oNPGoEducation,o2010.
http://www.nature.com/scitable/ebooks/essentials-of-cell-biology-14749010 8/9/2011
,EssentialsoofoCelloBiologyo|oLearnoScienceoatoScitable Pageo1oofo1
WhatoIsoaoCell?oWhatoAreotheoEssentialoCharacteristicsoofoCells
?
HowoDooCellsoDecodeoGeneticoInformationointooFunctionaloProteins?o
HowoAreoEukaryoticoCellsoOrganizedointooSmalleroParts?
HowoDooCellsoSenseoTheiroEnvironment?
How Do Cells Know When to Divide?
http://www.nature.com/scitable/ebooks/essentials-of-cell-biology-14749010/contents 8/9/2011
,Unito1oofoEssentialsoofoCelloBiologyo|oLearnoScienceoatoScitable Pageo1oofo2
EssentialsoofoCelloBiologyo o Contents
PROGRESS 20% 40% 60% 80% 100%
Prev Page
Unito1:o WhatoIsoaoCell?oWhatoAreotheoEssentialoCharacteristicsoofoCells? o
NextoPage
Whatoareotheseoliving ounitsocalledocells?oMucholikeomini-
fiefdoms,ocellsohaveoall otheoequipmentoandoexpertiseo necessaryotoocarryooutotheofunctionsoofolife.oAocelloca
noeat,ogrow,oandomove.oItocanoperformonecessaryo maintenance,orecycleoparts,oandodisposeoof owastes. oItocan
oadaptotoochanges oinoits oenvironment; oandoitocanoeveno replicate oitself.
Despiteotheseosimilarities,oallocellsoare onotoequal.oSome oare otrulyoself-sustaining,oasowithosingle-
celledobacteriao oroyeast,owhereasoothersoliveocommunally,osometimesoasopartoofocomplexomulticellularoorg
anisms.oCellsoalsoo differoinosize.oAlthoughocellsocanobeoquiteolargeo—
oconsideroaofrog'soegg,oforoexample o—
omost oareotooosmallotoo seeowithotheonaked oeye.oIndeed,otheodevelopment oofolight omicroscopyowasoessential o
tooman'sodiscoveryoofocells.
Don'tobeolulledobyofamiliaroschematicodrawingsoofooval-shapedocells,oeither.oRealocellsoareothree-
dimensional,oofo course,oandotheyoexistoinoaovarietyoofointricateoandoremarkableoshapes.oForoinstance,oaosin
gleohumanonerveocello canobeooverooneometerolong,oextendingofromoyourobackboneotooyourobigotoe.oComp
areothatowithotheocellsothato lineoyourosmallointestine, owhich ohave odozensoof otiny,ofingerlikeoprojections otoo
maximize otheosurfaceoareaoacrosso whichonutrientsocanopass.
Butohow,oexactly,odoocellsoaccomplishotheocomplexotasksoofolife?oWhatotoolsoandomaterialsodootheyoneed?oA
ndo whatoareotheokeyocharacteristicsothatodefineoaocell?oThisounitoanswersotheseoquestionsoandoprovidesoaob
asico overviewoofotheoinneroworkingsoofotheocell.
InoThisoUnit
CellsoAre otheoBasic oUnitsoofo L
ivingoOrganisms
EukaryoticoCellsoPossessoao N
ucleusoandoMembrane-
Boundo Organelles
CelloFunction oDependsoonoth
eo ContinualoUptakeoando C
onversionoofoEnergy
Photosynthetic oCellsoCaptureo
LightoEnergyoandoConvertoItoto
o Chemical oEnergy
MetabolismoisotheoCompleteoS
eto ofoBiochemicaloReactionso
withinoaoCell
Test oYouroKnowledge
http://www.nature.com/scitable/ebooks/essentials-of-cell-biology-14749010/what-is-a-cell-... 8/9/2011
, ContentsoofoEssentialsoofoCelloBiologyo|oLearnoScienceoatoScitable Pageo1oofo4
PROGRESS 20% 40% 60% 80% 100%
Treesoinoaoforest,ofishoinoaoriver,ohorsefliesoonoaofarm,olemursoinotheojungle,oreedsoinoaopond,owormsoinotheosoilo—
oallotheseo plantsoandoanimalsoareomadeoofotheobuildingoblocksoweocallocells.oLikeotheseoexamples,omanyolivingothings
oconsistoofovasto numbersoofocellsoworkingoinoconcertowithooneoanother.oOtheroformsoofolife,ohowever,oareomadeoofoonl
yoaosingleocell,osuchoaso theomanyospeciesoofobacteriaoandoprotozoa.oCells,owhetherolivingoonotheiroownooroasopartoofo
aomulticellularoorganism,oareo usuallyotooosmallotoobeoseenowithoutoaolightomicroscope.
Cellsoshareomanyocommonofeatures,oyetotheyocanolookowildlyodifferent.oInofact,ocellsohaveoadaptedooverobillionsoofoyear
sotooao wideoarrayoofoenvironmentsoandofunctionaloroles.oNerveocells,oforoexample,ohaveolong,othinoextensionsothatocano
reachoforo metersoandoserveotootransmitosignalsorapidly.oCloselyofitting,obrick-
shapedoplantocellsohaveoaorigidoouterolayerothatohelpso provideotheostructuralosupportothatotreesoandootheroplantsorequire.o
Long,otaperedomuscleocellsohaveoanointrinsicostretchinessothato allowsothemotoochangeolengthowithinocontractingoandorela
xingobiceps.
Still,oasodifferentoasotheseocellsoare,otheyoallorelyoonotheosameobasicostrategiesotookeepotheooutsideoout,oallowonecessary
o substancesoinoandopermitoothersotooleave, omaintainotheirohealth, oandoreplicateothemselves. oInofact, otheseotraitsoareoprecise
WhatoDefinesoaoCell?
Figureo1:oTransportoproteinsoinotheocellomembrane
Aoplasma omembraneoisopermeableotoospecificomolecules othatoaocellone
eds.o Transportoproteinsoinotheocellomembraneoallowoforoselectiveopass
ageoofo specificomoleculesofromotheoexternaloenvironment.oEachotranspo
rtoproteinoiso specificotooaocertainomoleculeo(indicatedobyomatchingocol
ors).
©o2010oNatureoEducationoAllorightsoreserved. o
Cellsoareoconsideredotheobasicounitsoofolifeoinopartobecauseotheyocomeoinodiscreteoandoeasilyorecognizableopackages.oT
hat'so becauseoallocellsoareosurroundedobyoaostructureocalledotheocellomembraneo—
owhich, omucholikeotheowallsoofoaohouse,oservesoaso aoclearoboundaryobetweenotheocell'sointernaloandoexternaloenvironme
nts.oTheocellomembraneoisosometimesoalsooreferredotooaso theoplasmaomembrane.
Cellomembranesoareobasedoonoaoframeworkoofofat-
basedomoleculesocalledophospholipids,owhichophysicallyopreventowater-
o loving,oorohydrophilic,osubstancesofromoenteringooroescapingotheocell.oTheseomembranesoareoalsoostuddedowithoprotein
sothato serveovariousofunctions.oSomeoofotheseoproteinsoactoasogatekeepers, odeterminingowhatosubstancesocanoandocannot
ocrossotheo membrane.oOthersofunctionoasomarkers,oidentifyingotheocelloasopartoofotheosameoorganismooroasoforeign.oStill
oothersoworkolikeo fasteners,obindingocellsotogetherosootheyocanofunctionoasoaounit.oYetootheromembraneoproteinsoserveoaso
communicators,osendingo andoreceivingosignalsofromoneighboringocellsoandotheoenvironmento—
owhetherofriendlyooroalarmingo(Figureo1).
Withinothisomembrane,oaocell'sointerioroenvironmentoisowaterobased.oCalledocytoplasm,othisoliquidoenvironmentoisopacke
dofullo ofocellularomachineryoandostructuraloelements.oInofact,otheoconcentrationsoofoproteinsoinsideoaocellofarooutnumber
othoseoonotheo outsideo—owhetherotheooutsideoisooceanowatero(asoinotheocaseoofoaosingle-
celledoalga)oorobloodoserumo(asoinotheocaseoofoaoredo bloodocell).oAlthoughocellomembranesoformonaturalobarriersoinow
ateryoenvironments,oaocellomustononethelessoexpendoquiteoa
http://www.nature.com/scitable/ebooks/essentials-of-cell-biology-14749010/16433178 8/9/2011
