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1. TRANSLATION
M.Prasad Naidu
MSc Medical Biochemistry, Ph.D,.

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

5. Requirements for TRANSLATION:
ribosomes
m-RNA
t-RNA
A.As
AMINOACYL t-RNA SYNTHETASES
ATP, GTP
ENZYMES OF TRANSLATION
PROTEIN FACTORS

6. TRANSLATION: Steps
1. ACTIVATION OF A.A
2.INITIATION
3.ELONGATION
4.TERMINATION
5.POST TRANSLATIONAL PROCESSING

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.

18. 80S ribosome
Ribosomal dissociation
40S subunit
Ternary complex

19. 60S
43S Preinitiation complex
48S Inititation complex
80S Inititation complex
Initiating codonCap
eIF4
eIF
eIF
eIF

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….

26. APPP
P P P
AA
A A A

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.

29. P P PA A A

30. POLYRIBOSOME (POLYSOME)

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.

33. THANK YOU