The document summarizes the process of translation in cells. It describes how the genetic code on mRNA is translated into a sequence of amino acids with the help of tRNA and ribosomes. There are several steps involved: 1) amino acids are activated by attaching to tRNA, 2) initiation begins with formation of initiation complexes on ribosomes, 3) elongation occurs as new amino acids are added one by one to the growing polypeptide chain through movement of tRNA between ribosomal sites, and 4) termination releases the full protein when a stop codon is reached. The entire process requires energy in the form of GTP hydrolysis at several steps.
2. THE LANGUAGE OF NUCLEOTIDE SEQUENCE ON
m-RNA ( GENTIC CODE ) IS TRANSLATED IN TO THE
LANGUAGE OF AMINIO ACID SEQUENCE.
3. t-RNA ( soluble RNA)
Transfer A.A from cytosol to the
ribosomal protein synthesising
machinery.
73 – 93 nucleotides in length
4. 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) SUBUNIT
SMALLER 40S (30S) SUBUNIT
7. ACTIVATION OF A.A
AMINOACYL t-RNA SYNTHETASE
A.A + t-RNA + ATP Aminoacyl t-RNA + AMP
8. 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
11. mRNA is read in 5’ to 3’ direction
PROTEIN SYNTHESIS TAKES PLACE
FROM N-TERMINAL TO C-TERMENAL END
12. 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
13. Steps involved in Initiation:
1. Ribosomal dissociation
2. Formation of 43S pre-initiation complex
3. Formation of 48S initiation complex
4. Formation of 80S initiation complex
14. Ribosomal dissociation:
eIF3 and eIF1 A binds to 40S subunit and
prevents the reassociation with 60S – causing
ribosomal subunit dissociation.
15. 2. Formation of 43S pre-initiation complex
GTP + eIF2
This complex binds to met-tRNA-I
This GTP-eIF2-tRNA-I complex binds to the 40S
ribosomal subunit to form 43S pre-initiation
complex.
16. 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, ATP
KOZAK CONSENSUS (EUKARYOTES) on mRNA
facilitates binding of mRNA to pre-initiation complex
SHINE DALGARNO SEQUENCE on mRNA facilitates
binding of mRNA to pre-initiation complex
17. 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.
20. P & A SITES
RIBOSOME CONTAINS 2 RECEPTOR SITES
FOR t-RNA MOLECULES
P (PEPTIDYL) SITE
A (AMINOACYL) SITE
Met-t-RNA OCCUPIES P SITE.
ALL OTHER t-RNAs OCCUPY A SITE
t-RNA BINDS WITH RIBOSOME THROUGH
THE PSEUDOURIDINE ARM
ANTICODON OF t-RNA & CODON ON m-RNA
BIND
A SITE IS FREE NOW.
24. ELONGATION:
BINDING OF NEW AMINOACYL t-RNA
CODON IN m-RNA DETERMINES THE INCOMING
A.A
EF 1 & GTP REQD.
PEPTIDE BOND FORMATION:
α-NH2 GROUP OF INCOMING A.A IN A SITE
FORMS PEPTIDE BOND WITH COOH GROUP OF
A.A IN P SITE.
ENZYME IS PEPTIDYL TRANSFERASE
NO NEED FOR ENERGY AS A.A IS ACTIVATED.
25. 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 CODON
PEPTIDYL 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 IN
ELONGATION CONTINUES….
27. ENERGY REQUIREMENTS:
ACTIVATION OF A.A 2 ATP
FOR PRE-INITIATION COMPLEX 1 GTP
FOR INITIATION COMPLEX 1 ATP
BINDING OF AMINOACYL t-RNA 1 GTP
TANSLOCATION PROCESS 1 GTP
28. TERMINATION;
SUCCESSIVE ADDITIONS OF A.A
TERMINATION CODONS REACHED.
NO t-RNA CORRESPONDING TO
TERMINATION CODON
A SITE REMAINS FREE
RELEASING FACTOR ENTERS A SITE
RELEASES THE PEPTIDE CHAIN WITH
HYDROLYSIS OF GTP.
RIBOSOME DISSOCIATES INTO 60 AND
40S
SUBUNITS.
32. PROTEIN TARGETTING:
PROTEINS FOR EXTERNAL SECRETION:
SYNTHESISED ON RER
SIGNAL PEPTIDE (LEADER sequence)
THRO ER, GOLGI
REACHES CORRECT DESTINATION.
INTERNAL PROTEINS:
LACK SIGNAL PEPTIDE
FREE RIBOSOMES
DO NOT ENTER ER. ARE AVAILLABLE IN
CYTOPLASM.