271211 - protein synthesis (translasi) - bu lely
TRANSCRIPT
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PROTEIN SYNTHESIS(TRANSLATION)
C-4 Tutorial Group
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The Characteristics of Codon
Degenerate multiple codons mustdecode the same amino acidUnambiguous given a specificcodon, only a single amino acid isindicatedNon-overlapping the process of protein synthesis does not involve anyoverlap of codons
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The Characteristics of Codon
Not punctuated the message is read ina continuing sequence of nucleotide tripletsuntil a translation stop codon is reached
Universal The frequency of use of eachamino acid codon varies considerablybetween species and among differenttissues within a species
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Components of Translation
Amino acid all amino acid must bepresent at the time of proteinsynthesistRNA attach to specific amino acid,contains anticodonAminoacyl-tRNA synthase attachthe amino acids to their corresponding tRNAs
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Components of Translation
mRNA as a template for thesynthesis of the polypeptide chainRibosom
rRNA structure of base-pairingRibosomal protein interact with other component of translation system
A-binding site aminoacyl tRNAP-binding site peptidyl tRNAE-site exit of the ribosome
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Components of Translation
Protein factors as catalytic factors/ enzymes
ATP & GTP source of energy
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Steps in Protein Synthesis
Initiation
Elongation
Termination
Postranslation Modification
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Initiation
The binding of GTP by eIF-2 binarycomplex
Binary complex then binds to met-tRNA ternary complexTernary complex binds to the 40Sribosomal subunit the 43S preinitiation
complexThe 43S preinitiation complex stabilized byassociation with eIF-3 and eIF-1A.
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Initiation
The association of mRNA with the 43Spreinitiation complex + ATP hydrolysis 48S initiation complex60S ribosomal subunit + 48S initiationcomplex + hydrolysis of the GTP bound toeIF-2 by eIF-5 = release of the initiationfactors bound to the 48S initiation complex
40S and 60S subunits to form the 80Sribosome
At this point, the met-tRNA i is on the P siteof the ribosome, ready for the elongationcycle to commence.
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Elongation
Binding of aminoacyl-tRNA to the Asiteaminoacyl-tRNA carries out anucleophilic attack on the esterifiedcarboxyl group of the peptidyl-tRNAoccupying the P site bypeptidyltransferase
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Elongation
elongation factor 2 (EF2) binds to anddisplaces the peptidyl tRNA from the A siteto the P site. In turn, the deacylated tRNA
is on the E site,from which it leaves theribosomethe energy requirements for the formationof one peptide bond = hydrolysis of two
ATP molecules to ADP and of two GTPmolecules to GDP = hydrolysis of four high-energy phosphate bonds.
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Termination
The elongation will stop terminatingcodon of mRNA if stop codons (UAA,UAG, UGA) appears in the A siteThe releasing complex (Releasingfactor RF1 + releasing factor RF3 +GTP) hydrolysis peptide bonds andrelease protein and dissociate the80S into 40S and 60S
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The Regulation of eIF-4EControls the Rate of InitiationThe 4F complex is particularly important in
controlling the rate of protein translation.4F is a complex consisting of 4E, which binds tothe m7G cap structure at the 5 end of the mRNA,
and 4G, which serves as a scaffolding protein.In addition to binding 4E, 4G binds to eIF-3, whichlinks the complex to the 40S ribosomal subunit.It also binds 4A and 4B, the ATPase-helicasecomplex that helps unwind the RNA.4E is responsible for recognition of the mRNA capstructure, which is a rate-limiting step intranslation.
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REGULATION ONTRANSLATIONAL STAGE
In eukaryotes, eukaryotic initiationfactor 2 (eIF2) is the center of regulation mechanism as eIF2 isneeded in initiation stage of proteinsynthesis.eIF2 can be inhibited byphosphorylation.
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REGULATION ON POST-TRANSLATIONAL STAGE
Post-translational modification isdefined as protein structure alterationafter being released by ribosome.
Modification takes place inendoplasmic reticulum and Golgiapparatus.
This modification can be classifiedinto two groups:Chemical modification.Protein folding.
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Posttranslational Modification
The result of translation proproteins require modifications before attainingbiologic activity
Kind of posttranslationalremoval amino acid residues byaminopeptidasesacetylationphosphorylationmethylationubiquitinylationglycosylation