BIOL 3301 - Genetics Ch14- Translation and Mutation 08 St

8/18/2019 BIOL 3301 - Genetics Ch14- Translation and Mutation 08 St

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Stages of translation• Initiation

– __ribosome recognition – proka ryotes: mRNA Shine- elgarno se!"ence #hich hy$rogen bon$s

#ith rRNA• e"karyotes: ribosome attaches to %& cap

– tRNA met bin$s to A'( co$on• N-formylmethionine "se$ in prokaryotes) tRNA f *et) later remo+e$• Initiation factors

• Elongation: "se of elongation factors an$ (T,• Termination

– ribosome pa"ses at stop co$on – release factor bin$s) comple $issociates


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Translation Initiation

• Initiation re!"irements: – mRNA molec"le – ribosome – Initiator tRNA – Three initiation factors

– (T, – *g ./


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Initiation• Small ribosomal s"b"nit bin$s to _se+eral initiation

factors_ • This comple bin$s to mRNA

• In prokaryotes initiation co$on _A'(_ calls for f-met 0N-formylmethionine1• Shine- algarno se!"ence A((A(( prece$es start

co$on in mRNA2 complementary se!"ence on 3&of

45S rRNA – __facilitates initiation____ • Initiation protein enhances bin$ing of f-met tRNA tothe small s"b"nit – sets the rea$ing frame –initiation comple


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AGGAGGU AUG

Ribosome bin$ing site

Initiationco$on

5’ 3’

3-46 n"cleoti$es

TRANSLATION INITIATION:

Bacteria

Translation factors:-initiation factors 0I7-4) I7-.) I7-31

-elongation factors 0E7-T") E7-Ts)E7-(1-release factors 0R7-4) R7-.) R7-31-ribosome recycling factor 0RR71


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Initiation 8omple

• 36S small s"b"nit bin$s __I74) I7.) I73• 36S /I7s bin$s to mRNA A'( co$on

region – A se!"ence "pstream of A'( is necessary) -9-

46 position –

%&en$ of %&'TR – ribosome-bin$ing site R S0Shine- elgarno se!"ence A((A( –p"rine-rich) complementary to '88'88 pyrimi$ine – rich region at 3&-en$ of 45S rRNA1


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Initiation 8omple

• Initiator tRNA bin$s to A'( start co$on – Initiator f*et

• *ethionyl-tRNA synthetase a$$ methionine totRNA

• Transformylase a$$s formyl gro"p to methionine – f*et-tRNA;f*et


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Initiation 8omple

• f*et-tRNA bin$s to A'( of 36S-mRNA comple )I73 is release$

• %6S s"b"nit bin$s – (T, hy$rolysis – I74) I7. release$

• 7inal comple –


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Translation Initiation In acteria


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12/35PowerPoint ® Layered Art


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Elongation In ,rokaryotes

• Antico$on of f*et-tRNA is hy$rogen-bon$e$ toA'( in , site

• Ne t co$on is in A site • 8omplementary tRNA bin$s to A site• tRNA is bo"n$ to protein elongator factor E7-T"

• aa-tRNA bin$s to A site) (T, hy$rolysis) releaseof E7-T"-( , 0recycling1


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Elongation

• Aminoacyl tRNA bin$s to A site• (ro#ing chain of polypepti$e is transferre$ from

tRNA in , site to tRNA in A site by forming a ne# pepti$e bon$

• Ribosome translocate along mRNA to positionne t co$on against A site

• tRNA translocate from A-, to ,-E sites• Elongation factor E7-T"•(T, pro+i$e energy


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Translocation

• Ribosome mo+es one co$on to#ar$s _3& en$_ • Re!"ire acti+ity of protein elongation factor E7-(

• E7-(-(T, bin$s to the ribosome) (T, is hy$roly>e$• 'ncharge$ tRNA is $isplace$ a#ay from , site)

bin$s to E site) blocks neat aa-tRNA from bin$ing toA-site "ntil translocation is complete an$ pepti$yl-

tRNA is bo"n$ in , site• After translocation – E7-( is release$ "sing (T, hy$rolysis an$ recycle$


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Termination• 8hain-termination co$ons 'AA) 'A() '(A enter A

site• Recogni>e$ by release factors R7s 0Rf4 an$ Rf.2 only

one in e"karyotes eR71• ,resence of release factor ca"ses the acti+ity change

of pepti$yl transferase) a$$ #ater to carbo yl of polypepti$e chain

• Reaction releases polypepti$e from tRNA in the , site• 7ree tRNA mo+es to E site) mRNA release$) ribosome

$issociate


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Termination

• ) – Ribosome Recycling 7actor

– Elongation 7actor ( 0E7-(1• f"nction to release mRNA an$ tRNAs from

ribosomes an$ $issociate the


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Termination

• I7-3 also helps the ribosome-recycling process by con+erting transiently

$issociate$ s"b"nits into stable ones by bin$ing to __36S s"b"nits???_;• This @recycles@ the ribosomes for a$$itional

ro"n$s of translation


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PowerPoint ® Layered Art


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Ribo>ymes

• A catalytic RNA – RNA en>yme• 45S rRNA – catalysis of pepti$e bon$• Release factor – RNA molec"le similar to

tRNA• Ribon"clease , - that clea+es the hea$ 0% 1

en$ of the prec"rsors of transfer RNA0tRNA1 molec"les

• snRN,s -


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Translation In E"karyotes

• Similar) more __more initiation factors_ • tRNA *et is not f*et – tRNAs co$e$ by

t#o $ifferent genes• Initiation comple starts at A'( closest to

the %&en$

• Bptimal initiation se!"ence %&-(880AC(188A'(8-3&

• ( – increase efficiency) Do>ak r"les


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• tRNA i*et / I7----- , site $irectly• %&cap bin$ing protein 8 , 0part of eI7- 7 initiation

comple 1 bin$s to


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• 96S initiation comple #ith *et-tRNA bo"n$ to mRNA #ith A'( in , site

• polyA tail is bo"n$ by poly0A1bin$ing protein 0,A ,1) bin$s to eI7- (

• Initiation of translation is stim"late$


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Interaction of 3 an$ % en$s of mRNA

important in initiation of translation;


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Translation

• ,rokaryotes – ribosomes are smaller – translation is co"ple$ to

transcription – more than one gene may be

translate$ from the samemRNA

– translation is polycistronic

– the Shine- elgarno se!"encealigns mRNA on ribosome – the first amino aci$

incorporate$ is N-formylmethionine

• E"karyotes – translation monocistronic – ribosomes recogni>e

mRNA by bin$ing to


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*"tations


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*"tations

• 8hange in genetic material -a m"tation is an __alteration in NA se!"ence_;

• So"rce of genetic +ariability• No+el phenotype _m"tant_


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*"tations

• Somatic or germinal – Somatic: melanoma - cannot be passe$ $o#n

generations – (erminal: – ray – affects germ cells – yo" #o"l$n&t be

affecte$ – chil$ren #ill be

• Spontaneo"s or in$"ce$

• Re+ersible: happens more often in prokaryotes – prototrophs or a" otrophs

• (ain of f"nction) loss of f"nction) ne"tral


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,oint *"tations

• A$$ition• eletion• S"bstit"tion• 7rame-shift

– *issense

– Nonsense – Ne"tral – silent

BIOL 3301 - Genetics Ch14- Translation and Mutation 08 St

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