TRANSLATION
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Transcript of TRANSLATION
THE LANGUAGE OF NUCLEOTIDE SEQUENCE ON m-RNA ( GENTIC CODE ) IS TRANSLATED IN TO THE LANGUAGE OF AMINIO ACID SEQUENCE.
t-RNA ( soluble RNA)
Transfer A.A from cytosol to the ribosomal protein synthesising machinery.
73 – 93 nucleotides in length
RIBOSOMES
INFRASTRUCTURE FOR THE m-RNA, t-RNA & A.A TO INTERACT WITH EACH OTHER FOR TRANSLATION.
80S IN EUKARYOTES & 60S IN PROKARYOTES.LARGER 60S (50S) SUBUNITSMALLER 40S (30S) SUBUNIT
Requirements for TRANSLATION: ribosomesm-RNAt-RNA A.AsAMINOACYL t-RNA SYNTHETASESATP, GTPENZYMES OF TRANSLATIONPROTEIN FACTORS
TRANSLATION: Steps 1. ACTIVATION OF A.A2.INITIATION 3.ELONGATION 4.TERMINATION5.POST TRANSLATIONAL PROCESSING
ACTIVATION OF A.A
AMINOACYL t-RNA SYNTHETASE
D ARM OF tRNA RECOGNISED BY THE ENZYME
A.A + t-RNA + ATP Aminoacyl t-RNA + AMP
ENZYME IDENTIFIES THE SPECIFIC t-RNA TRANSFERS AMINOACYL GROUP TO 3’ END CCA
-COOH GROUP OF A.A ESTERIFIED WITH THE 3’ OH GROUP OF t-RNA.
AT LEAST 1 ENZYME FOR 1 A.A
INITIATION:
Basic requirements for initiation
Ribosome mRNA to be translated The initiating Met-tRNA A set of protein factors called initiation factors. In Eukaryotes there are at least nine factors,
designated e If to indicate eukaryotic origin. In prokaryotes, three initiation factors are
known IF1, IF2 and IF3
Steps involved in Initiation:
1. Ribosomal dissociation2. Formation of 43S pre-initiation complex3. Formation of 48S initiation complex4. Formation of 80S initiation complex
Ribosomal dissociation:
eIF3 and eIF1 A binds to 40S subunit and prevents the reassociation with 60S – causing ribosomal subunit dissociation.
2. Formation of 43S pre-initiation complex
GTP + eIF2 This complex binds to met-tRNA-IThis GTP-eIF2-tRNA-I complex binds to the 40S ribosomal subunit to form 43S pre-initiation complex.
3. Formation of 48S initiation complex
Binding of m-RNA to 43S pre-initiation complex forms 48S initiation complex.
5’ end of m-RNA contains CAP which helps in binding of m-RNA to 43S pre-initiation complex.
The association of mRNA with 43S initiation complex requires:
CAP binding protein, eIF4, ATPKOZAK CONSENSUS (EUKARYOTES) on mRNA
facilitates binding of mRNA to pre-initiation complexSHINE DALGARNO SEQUENCE on mRNA facilitates
binding of mRNA to pre-initiation complex
4. FORMATION OF 80S RIBOSOME ASSEMBLY
48S INITIATION COMPLEX + 60S RIBOSOME. + e-IF2 + e-IF5.
e-IF 5 HAS GTPase ACTIVITY.GTP BOUND IN STEP 1 HYDROLYSED FOR ENERGY.
ALL INITIATION FACTORS NOW RELEASED.
NEXT STAGE IS ELONGATION.
60S
43S Preinitiation complex
48S Inititation complex
80S Inititation complex
Initiating codonCap
eIF4eIF
eIF
eIF
P & A SITESRIBOSOME CONTAINS 2 RECEPTOR SITES FOR t-RNA MOLECULESP (PEPTIDYL) SITEA (AMINOACYL) SITEMet-t-RNA OCCUPIES P SITE.ALL OTHER t-RNAs OCCUPY A SITEt-RNA BINDS WITH RIBOSOME THROUGH THE PSEUDOURIDINE ARMANTICODON OF t-RNA & CODON ON m-RNA BIND A SITE IS FREE NOW.
ELONGATION:BINDING OF NEW AMINOACYL t-RNA
CODON IN m-RNA DETERMINES THE INCOMING A.A
EF 1 & GTP REQD.
PEPTIDE BOND FORMATION:-NH2 GROUP OF INCOMING A.A IN A SITE
FORMS PEPTIDE BOND WITH COOH GROUP OF A.A IN P SITE.
ENZYME IS PEPTIDYL TRANSFERASENO NEED FOR ENERGY AS A.A IS ACTIVATED.
TRANSLOCATION: WHEN PEPTIDE BOND FORMED Met FROM P SITE SHIFTED TO A SITE.
t RNA IS RELEASED FROM P SITE, NOW P SITE FREE
RIBOSOME MOVES FORWARD BY 1 CODONPEPTIDYL t-RNA TRANSLOCATED TO P
SITE.NOW A SITE EMPTY
NEW AMINOACYL t-RNA WILL COME ONLY TO A SITE.
STEP REQUIRES EF 2 AND ENERGY FROM GTP.
NEW AMINOACYL t-RNA CAN COME INELONGATION CONTINUES….
ENERGY REQUIREMENTS:
ACTIVATION OF A.A 2 ATPFOR PRE-INITIATION COMPLEX 1 GTPFOR INITIATION COMPLEX 1 ATPBINDING OF AMINOACYL t-RNA 1 GTPTANSLOCATION PROCESS 1 GTP
TERMINATION;SUCCESSIVE ADDITIONS OF A.ATERMINATION CODONS REACHED.NO t-RNA CORRESPONDING TO TERMINATION CODONA SITE REMAINS FREERELEASING FACTOR ENTERS A SITERELEASES THE PEPTIDE CHAIN WITH HYDROLYSIS OF GTP. RIBOSOME DISSOCIATES INTO 60 AND 40S SUBUNITS.
PROTEIN TARGETTING:PROTEINS FOR EXTERNAL SECRETION:SYNTHESISED ON RERSIGNAL PEPTIDE (LEADER sequence)THRO ER, GOLGIREACHES CORRECT DESTINATION.
INTERNAL PROTEINS:LACK SIGNAL PEPTIDEFREE RIBOSOMESDO NOT ENTER ER. ARE AVAILLABLE IN CYTOPLASM.