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Introduction to the Study of

Cells

Chapter 1

Pages 1-24


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Discovery of Cells RobertHooke:corkcomposedofsmallchambersReportedin1665

Madepossiblebydevelopmentofmicroscope

Termedporouschambers"cells"Actuallyobservedcellwalls


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Anton van Leeuwenhoek: first descriptions

of cellsGroundlensesashobby

Observedprotistsinpondwatertermed"animacules"


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Importance of cells realized in 1830s with

publication of 2 papersMatthiasSchleiden:plantscomposedofcells

TheodorSchwann:first2tenetsofcelltheory Allorganismsarecomposedofoneormorecells

Thecellisthestructuralunitoflife

Schleiden Schwann


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Rudolf Virchow: third tenet of cell theory in1855

Cellscanariseonlybydivisionofapreexistingcell


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Basic Properties of Cells

1. Highlycomplexandorganized

Differentlevelsoforganization

atoms molecules macromolecules complexes organelles cells tissues

Mostbasicprocessesandstructuresremarkablysimilarinallorganisms

Informationfromoneorganismgenerallyapplicabletootherorganisms

Modelorganismsforintensiveinvestigation


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Bacterium

Escherichia coli

Yeast

Saccharomycescerevisiae

Model Organisms


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Nematode

Caenorhabditis elegans

Flowering PlantArabidopsis


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Basic Properties of Cells2. Possessgeneticprogramandmeanstouseit

Genesblueprintsforcellularconstruction&activities

3. Capableofreproduction

4. Acquire

and

utilize

energy

Requireconstantinputofenergy

Conversionofelectromagneticradiationtochemical

energystored

in

carbohydrates

Conversionofstoredchemicalenergyintousableformforcellularactivities(usuallyATP)


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5. Carryoutavarietyofchemicalreactions

Sumtotalofchemicalreactionsincellmetabolism

6. Engageinnumerousmechanicalactivities

Structuresassembledanddisassembled

Materialstransportedfromplacetoplace

Manycellsmove7. Respondtostimuli

Receiveandreacttosignalsfromothercellsandtheenvironment

8. Capableofselfregulation

Obviouswhenregulatorymechanismsbreakdown


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Two Classes of Cells Basedoninternalcomplexity

Prokaryoticcellsofarchaebacteriaandeubacteria

Eukaryoticcellsofallotherorganisms

Namefrompresence/absenceofnucleus Karyon=kernelornucleus

Pro

=

before Eu=wellortruly


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Common Characteristics of Prokaryoticand Eukaryotic Cells

1. Similarconstruction

of

plasma

membrane

2. GeneticinformationencodedinDNA

3. Similarmechanisms

for

synthesizing

proteins

transcriptionandtranslation

Madebyribosomessimilarbutnotidenticalin

prokaryoticand

eukaryotic

cell

4. Sharemetabolicpathways


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Common Characteristics of Prokaryoticand Eukaryotic Cells

5. Similarmechanism

for

ATP

production

6. Similarmechanismofphotosynthesis

(cyanobacteria

and

green

plants)7. Similarmechanismforsynthesizingand

insertingmembraneproteins

8. Similarproteasomesstructuresfordigestion

ofproteinsincytosol


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Unicellular eukaryotic organisms range fromrelatively simple (yeast)

to perhaps the most complex ofall cells (protozoa and algae)

Eukaryotic cells more complex


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Activities of multicellular organisms dividedamong different types of specialized cells


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Features of Eukaryotic Cells not Found inProkaryotes

OrganizationofDNA

Longlinearstrandsassociatedwithproteins

Capableofcondensingintomitoticchromosomes


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DNAsegregatedinnucleus

Complexmembranedelimitedorganellesin

cytoplasm


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Specializedorganellesforaerobicrespirationand

photosynthesismitochondria

and

chloroplasts

ContainownDNAandproteinsynthesizingmachinery

Divide

to

increase

number

Believedtohavecomefromprokaryoticcellsengulfedbyeukaryoticancestor

mitochondria chloroplast


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Endoplasmicreticulum(ER)systemofinterconnectedflattened

sacs

and

tubes

Originof mostcellmembranecomponentsandmaterialsexportedfromcell

SmoothversusRoughER dependentonpresenceofribosomes


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Golgiapparatus

Stackofflattenedsacs ReceivesmoleculesfromERanddirectsthemappropriate

destination

Oftenmodifiesmoleculesinprocess


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Lysosomes(protozoaandanimalcells)

Oftenirregularlyshapedwithheterogeneousinterior Sitesofintracellulardigestion

Peroxisomes Membraneboundedwithgranularinteriorandoftenwith

crystallinecore

Siteofchemicalreactionscoupledtosynthesisand

degradationof

hydrogen

peroxide


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Vacuoles(serveaslysosomesinplantcells)

Differenttypesofsmallvesiclesfortransportbetweenorganelles

Processesofendocytosisforingestingfluidandparticulatematerial,andexocytosisforreleaseof

materialfromcell

2003 Encyclopedia Br itannica, Inc.


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actin filaments microtubules intermediate filaments

Complexcytoskeletalsystem

Givescellmechanicalstrength

ControlscellshapeOrganizescytoplasmDrivesandguidesmovements


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Major Differences in Features ofProkaryotic & Eukaryotic Cells

Eukaryotic Structureofciliaand

flagellacomplex

Cellulosiccellwallwhenpresent

Multiplechromosomes

Prokaryotic Bacterialflagellaless

complex

Peptidoglycancellwallusuallypresent

Singlecircularchromosome


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Major Differences in Features ofProkaryotic & Eukaryotic Cells

Eukaryotic Mitosisutilizing

microtubulecontaining

spindle

Sexualreproductioninvolvingmeiosisand

fertilization

Prokaryotic DuplicatedDNAseparated

bygrowthof cell

membrane

CapableofexchangingpiecesofDNAbutnotrue

sexualreproduction


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Unique Characteristics of Archaea Cellwallsdonotcontainpeptidoglycan;contain

auniquemolecularstructureunlikeeubacteria

oreukaryotes Slayer

DNAisassociatedwithhistonelikeproteins

ProteinsynthesizingenzymesandRNApolymerasesmorecloselyresemblethoseof

eukaryotes

Membranelipidsareunique,resembling

neithertheeubacteria oreukaryotes


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Unique Characteristics of Archaea

Oftenreferredtoasextremophilesbecauseof

theenvironmenttheyliveinandthematerials

theyutilize

for

energy

(sugar,

ammonia,

sulfur,

hydrogen,metals)

Methanogens oxygenispoisonoustothem

Halophiles liveinhighsaltenvironments

Thermoacidophiles orThermophiles Cannot

surviveat

low

temperatures

(55C)

Endoliths liveinsiderocks,canutilizemineralsor

metalsasanenergysource.


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3 Domain System

ProposedbyCarlWoesein1990


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Cells are small

Diameter of a sphere in microns (m)

Vo

lumeofa

spherein

nanolite

rs(nL)

100 m diameter = 0.52 nL

300 m diameter = 14.14 nL

3X versus 27X

1 m = 10-6 meters1 nm = 10-9 meters

1 = 10-10 meters


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Cells are small Synthesisoflimitednumberofmessagesfromset

amountDNAinagiventime

Thelargerthevolume,thelongerthetimerequiredtomakenumberofmRNAsneededbycell

Decreaseinsurfacearea/volumeratiowithincreasein

size Surfacenotsufficienttotakeupsubstancesrequiredfor

metabolicactivitiesbeyondcertainsize

Diffusionresponsibleformovementofmanysubstancesintoandoutofcell Timerequiredfordiffusionproportionaltosquareofdistance

traversed


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Viruses

Smallerandsimplerthanbacteria

Wide

variety

of

shapes

andsizes

ObligateIntracellularparasites

Outsidecell Virion=geneticmaterial+proteincoat(capsid)

Ds

or

Ss

RNA/DNA NOreproduction,metabolism,anyactivitiesassociatedwithlife


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Human Immunodeficiency

Virus (HIV)

Bacteriophage


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Viruses Mosthavenarrowhostrange;changecanbe

devastating 1918flupandemic(25%ofthe

worlds

population

infected;

3%

died

50

100

millionpeople.

TwotypesofinfectionLytic

StableIntegration(severaloutcomes)

Viroids RNAonly