Classification three domain system

Based on 16S rRNA there are three domains of life: Bacteria (also known as Eubacteria), Archaea, and Eukarya.

1. Introduction To Three Domain System
DivyaChetnani
M.ScBT, Department of Biotechnology
Shree M & N ViraniScience College(Autonomous),
Rajkot -360005, Gujarat, India.
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Divya Swaminarayan

2. History Of PhylogeneticClassification
•Untilthemiddleofthe20thcentury,biologistsclassifiedalllivingthingsaseithera
plantorananimal.Butthissystemfailedtoaccommodatefungi,protistsand
bacteria.
•In1969.,theclassificationsystemevolvedtowhatwasknownasFiveKingdoms
—prokaryotes(bacteria)andeukaryotes(plants,animals,fungi,
protists).
•Eukaryotesarecharacterizedbythepresenceofnuclei,cytoskeletons,andinternal
membranesintheircells.
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3. •Inthelate1970s,Dr.CarlWoeseandhiscolleagues
attheUniversityofIllinoisidentifiedagroupof
microorganismswhosegeneticmakeupwasvastly
differentfromotherbacteria.
•Sotheydividedprokaryoticlifeintowhattheycalled
archaeabacteriaandeubacteria.
•However,theylaterconcludedthat"archaeabacteria"
weresufficientlydifferentastonotbebacteriaatall.So
thegroupswererenamedtoarchaeaandbacteria.
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4. Therearethreedomainsoflife:Bacteria(alsoknownasEubacteria),Archaea,and
Eukarya.
TheBacteriaandArchaeaaremadeupentirelyofmicroorganisms;the
Eukaryacontainsplants,animals,andmicroorganisms suchasfungiand
protists.
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5. •Archaeaweresplitoffasathirddomainbecauseofthelargedifferencesintheirribosomal
RNAstructure.TheparticularRNAmoleculesequenced,knownas16srRNA,ispresentinall
organismsandalwayshasthesamevitalfunction,theproductionofproteins.
•Becausethisfunctionissocentraltolife,organismswithmutationsofits16srRNAare
unlikelytosurvive,leadingtogreatstabilityinthestructureofthisnucleotideovermany
generations.
•Functions:
•Like thelarge (23S) ribosomal RNA, it has a structural role, acting as a scaffold defining the
positions of theribosomal proteins.
•Interacts with 23S, aiding in the binding of the two ribosomal subunits (50S+30S)
•16srRNAisalsolargeenoughtoretainorganism-specificinformation,butsmallenoughto
besequencedinamanageableamountoftime.
•In1977,CarlWoese,amicrobiologiststudyingthegeneticsequencingoforganisms,
developedanewsequencingmethodthatinvolvedsplittingtheRNAintofragmentsthat
couldbesortedandcomparedtootherfragmentsfromotherorganisms.
•Themoresimilarthepatternsbetweenspecieswere,themorecloselyrelatedtheorganisms.
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6. •Archaea:ArchaeaisderivedfromtheGreekwordarchaios,meaning
“ancient”or“primitive,”andindeedsomearchaeaexhibitcharacteristics
worthyofthatname.
•Membersofthearchaeainclude:Pyrolobusfumarii,whichholdstheupper
temperaturelimitforlifeat113°C(235°F)andwasfoundlivingin
hydrothermalvents.
•SpeciesofPicrophilus,whichwereisolatedfromacidicsoilsinJapanand
arethemostacid-tolerantorganismsknown—capableofgrowthataround
pH0.
•Andthemethanogens,whichproducemethanegasasametabolicby-
productandarefoundinanaerobicenvironments,suchasinmarshes,hot
springs,andthegutsofanimals,includinghumans.
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7. •Eubacteria:Eubacteria,knownas"truebacteria,"are
prokaryotic(lackingnucleus)cellsthatareverycommonin
humandailylifekillthousandsuponthousandsofpeople
eachyear,butalsoserveasantibioticsproducersandfood
digestersinourstomachs.
•WeuseEubacteriatoproducedrugs,wine,andcheese.
•Theylacksamembrane-boundnucleus(karyon),mitochondria,or
anyothermembrane-boundorganelle.
•Eukaryote:Aeukaryoteisanyorganismwhosecellshave
anucleusandotherorganellesenclosedwithinmembranes.
•EukaryotesbelongtothetaxonEucaryaorEukaryota.
•Thedefiningfeaturethatsetseukaryoticcellsapart
fromprokaryoticcells(BacteriaandArchaea)isthattheyhave
membrane-boundorganelles,especiallythenucleus,whichcontains
thegeneticmaterialandisenclosedbythenuclearenvelope.
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9. •Archaeaandbacteriaaregenerallysimilarinsizeand
shape,althoughafewarchaeahaveverystrangeshapes,such
astheflatandsquare-shapedcellsofHaloquadratum
walsbyi.
•TheRNApolymeraseinarchaeaissimilartoRNApolymeraseIIin
eukaryotes.
•Archaearesembleseukaryotesmorethanbacteria.Theirribosomeswork
morelikeeukaryoticribosomesthanbacterialribosomes.
•LipidsinmembranesfromArchaeaareunique,containingetherlinkages
betweentheglycerolbackboneandthefattyacids,insteadofester
linkages.
•ThecellswallsofArchaeaarechemicallyandstructurallydiverseanddonot
containpeptidoglycan.
Haloquadratum walsbyi.
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10. •Despitethismorphologicalsimilaritytobacteria,archeae
possessgenesandseveralmetabolicpathwaysthatare
morecloselyrelatedtothoseofeukaryotes,notably
theenzymesinvolvedintranscriptionandtranslation..
•Archaeareproduceasexuallybybinaryfission,fragmentation,
orbudding;unlikebacteriaandeukaryotes,noknown
speciesformsspores.
•AlthoughArchaeaareprokaryotic,theyaremore
closelyrelatedtoEukaryaandthuscannotbeplaced
withineithertheBacteriaorEukaryadomains.
•Hereareothermajordifferencesbetweenthethreedomains.
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11. Characteristic Eubacteria Archeae Eukaryotes
Cell Type Prokaryote Prokaryote Eukaryote
Cell size Usually0.5-4µ Usually0.5-4µ >5µ
Cell wall Made of
peptidoglycan
Does not contain
peptidoglycan
In plants and
fungi, composed of
polysaccharides
First amino acid
during protein
synthesis
FormylmethionineMethionine Methionine
DNA Mostly circular
chromosome and
plasmids
Circular
chromosome and
plasmids
Linear
chromosome,
rarely plasmids
Histones No Yes Yes
Organelles No No Yes
Ribosomes 70S 70S 80S
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12. Predominantly
multicellular
no no yes
Membranelipids
ester-linked*
yes
No (Archaea
membrane lipids
are ether-linked)
yes
Photosynthesiswith
chlorophyll
yes no yes
Growth above 80
o
C yes yes no
Operons yes yes no
Cappingandpoly-A
tailingof mRNA
no no yes
Transcription
factorsrequired
yes no yes
Methanogenesis no yes no
Nitrification yes no no
Intronsint-RNA absent present present
Intronsin m-RNA absent absent present
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13. Cappingandpoly-
A tailingof mRNA
no no yes
Transcription
factorsrequired
yes no yes
Methanogenesis no yes no
Nitrification yes no no
Denitrification yes yes no
Nitrogen Fixation yes yes no
Chemolithotrophy yes yes no
Gas vesicles
present
yes yes no
Sensitive to
chloramphenicol,
kanamycinand
streptomycin
yes no no
Sensitiveto
anisomysin
no yes yes
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14. Cytological
features
Eubacteria Archeae Eukaryotes
Nucleus No No Yes
Cytoskeleton No No Yes
Organelles
(mitochondria,chlo
roplasts,Golgi
apparatus,endopla
smic reticulum)
No No Yes
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15. Molecular
features
DNA topology
Negatively
supercoiled
Relaxed or
positively
supercoiled (in
hyperthermophilic
Archaeathat
contain reverse
gyrase)
Negatively
supercoiled
Promoterstructure
Two conserved
boxes at -10
(TATAAT) and -35
(TTGACA) from
transcription start
site
TATA box and/or
initiator element
TATA box and/or
initiator element
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16. RNA polymerase
One type;
relatively simple
subunit
composition; binds
directly to
promoter (can be
footprinted)
One type; complex
subunit structure
(subunit pattern,
genes, and
serological
properties similar
to eukaryalRNA
polymerase II)
Three types;
complex subunit
compositions
Poly(A)tails
inRNA
Short
Short (avg. 12
bases in length)
Long
Typical Organisms
Entricbacteria and
cyanobacteria
Methanogens,halo
philes,extremophil
es
Algae, Protozoa,
Fungi,Plants and
Animals
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