translation

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TRANSLATION IN PROKARYOTE AND EUKARYOTE

SAURAV SAHA COLLEGE OF HORTICULLTURE DEPERTMENT OF CPBMB 2014-11-106

1/7/2015

Translation

Conversion of mRNA base sequence into protein amino acid base sequence is called translation. it involved a stepwise reading of the message present in mRNA base sequences in codon and translating into a amino acid sequence in protein.

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Necessary material for the translation process

Amino acidRibosomemRNAt -RNA several translation factor

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About Ribosome

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StopStart

mRNA

Polycisronic

Monocistronic 6

mRNA The site where the ribosome bind is name

Shine-Dalgarno sequence.It is only present in a prokaryotic

mRNA.Shine–Dalgarno sequence – The polypurine

sequence AGGAGG centered about 10 bp before the AUG initiation codon on bacterial mRNA.It is complementary to the sequence at the 3′ end of 16S

rRNA. 7

Shine-Delgarno element

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Eukaryotic mRNA scanning

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About tRNA

The main important think in tRNA structure is the amino Acid acceptor region and anticodon region in the translation process.

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Mechanism of Translation

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A U G G G C U U A A A G C A G U G C A C G U U

This is a molecule of messenger RNA.

It was made in the nucleus by transcription from a DNA molecule.

mRNA molecule

codon

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A U G G G C U U A A A G C A G U G C A C G U U

.

ribosome

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A U G G G C U U A A A G C A G U G C A C G U U

It brings an amino acid to the first three bases (codon) on the mRNA.

Amino acid

tRNA molecule

anticodon

U A C

A transfer RNA molecule arrives.

The three unpaired bases (anticodon) on the tRNA link up with the codon.

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A U G G G C U U A A A G C A G U G C A C G U U

A peptide bond forms between the two amino acids.

Peptide bond

C C G U A C

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A U G G G C U U A A A G C A G U G C A C G U U

The first tRNA molecule releases its amino acid and moves off into the cytoplasm.

C C G U

A C

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A U G G G C U U A A A G C A G U G C A C G U U C C G

The ribosome moves along the mRNA to the next codon.

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A U G G G C U U A A A G C A G U G C A C G U U

Another tRNA molecule brings the next amino acid into place.

C C G

A A U

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A U G G G C U U A A A G C A G U G C A C G U U

The polypeptide chain gets longer.

G U C

A C G

The process continues.

This continues until a termination (stop) codon is reached.

The polypeptide is then complete.

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Initiation in prokaryotic For the initiation it require mRNA. The initiator tRNA. Three initiation factor(IF1,IF2, IF3). Large and small unit of ribosome .

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Initiation process in prokaryoticmRNA gets bind on smaller

subunit and IF1 and IF3 bind to 30S subunit

IF2 complexed with GTP then bind to the small subunits, forming a complex at RBS.

The initiator tRNA can then bind to the complex at the P site paired with AUG codon.

The 50S subunits can now bind. GTP is then hydrolyzed and IFs are released to give the 70S initiation complex

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Elongation processAn aminoacetyle-tRNA with EF-TU-GTP

complex binding in A site of ribosome.Then formation of peptide bond between two

amino acid with the help of peptidyl transferase enzyme which is the function of the 50 s ribosome.

Then after the peptide bond formation t-RNA released from the p site.

Then t-RNA from the A site moved to P site along with the movement of corresponding m-RNA making A site free for the new incorporation of aa-t-RNA, this process called translocation and factor associate with

EF-G with GTP complex.22

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Termination Termination is signalled by the three termination codon (UAG, UAA,UGA) and mediate by the release factor(RF1,RF2,RF3) .

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Function of the different release factor

RF1 or RF2 – The bacterial release factor that recognizes UAA and UAG and UGA as signals to terminate polypeptide translation.

RF3-

It functions to release the factors RF1 or RF2 from the ribosome when they act to terminate polypeptide translation.

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FUNCTION OF DIFFERENT FACTOR IN PROKARYOTIC TRANSLATION

Initiation factorIF-1 prevent premature entry of the t-RNA into A site

IF-2 directs the initiator t-RNA to its correct position of the initiation complex

IF-3 prevent pre mature association of the ribosome unit

Elongation factor

EF-TU direct the next t-RNA to its correct position in the ribosome.

EF-TS regenerate the EF-TU factor

EF-G mediate the translocation

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Conti……Release factorRF-1 recognize the termination codon UAA,

UAGRF-2 recognize the UAA , UGA codonRF-3 stimulate the dissociation of the Both the

factorRibosomal recycling factor RRF responsible for the dissociation of the

ribosomal subunit after translation has terminate

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Initiator tRNA+eIF2+GTP eIF3+40S

(Ternary complex)

43S pre initiation complex

+mRNA+eIF4F+eI

F4B

ATP

ADP+Pi

48S pre initiation complex

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Initiation process in eukaryotic

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Scanning

More factors involved

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Scanning to find AUG

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Elongation in eukaryotic

Elongation same as prokaryotic but only difference is the factorThe factors EF-Tu EF-Ts EF-G have direct eukaryotic equivalents called eEF1α, eEF1βγ, eEF2.

Termination

Termination is also similar to the prokaryotic , but here only one release factor

eRF instead of three release factor RF 1 RF 2 RF3

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Prokaryotic factor

Eukaryotic factor Function

IF1

IF2

IF3

eIF1 eIF1A

eIF2 eIF2B

eIF3 eIF4C

eIF4A eIF4B, eIF4F eIF5

Block the A site

Help to bind Met-tRNA

First to bind and prepare 40S for subsequent factors

As eIF1 eIF1A

Help dissociate IF2, eIF3,

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Initiation factors

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Elongation factorsProkaryotic factor

Eukaryotic factor

Function

EF-Tu

EF-Ts

EF-G

eEF1α

eEF1βγ

eEF2

A delivery of Aminoacyl tRNA to ribosome

Aiding the Recycling of EF-Tu or eEF1α

Translocation

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Termination factorsProkaryotic factor

Eukaryotic factor

Function

RF1, RF2, RF3 eRF 1Release of complex polypeptide chain

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Comparison prokaryotic and eukaryotic translation

Prokaryotic Eukaryotic

It occur on 70S ribosome It occur on 80S ribosome

It is a continuous process both transcription and translation occur in cytoplasm

It is a discontinuous process both transcription occur in nucleus and translation in cytoplasm

mRNA polycistronic mRNA monocistronic

First amino acid taking part is fMet

First amino acid taking part is Met

It is a first process 20 amino acid per second

It is a slow process 6 amino acid per second

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It require three initiation factorIF1, IF2, IF3.

It require nine initiation factor

It require three release factor RF1 RF2

It require one release factor eRF 1

mRNA life is short few seconds to few minutes

mRNA life span is few hour to few days

Cont……….

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