Translation is the process by which the nucleotide sequence of mRNA is used as a template to synthesize a polypeptide according to the genetic code. It involves three main steps: initiation, elongation, and termination. Initiation requires numerous initiation factors and begins with formation of the initiation complex containing the small ribosomal subunit, initiator tRNA, and mRNA. Elongation cycles then add amino acids to the growing polypeptide chain through binding of aminoacyl-tRNAs according to the mRNA codon sequence. Termination occurs when a stop codon is recognized, leading to peptide release and ribosome dissociation.

1. Eukaryotic translation
SUKHVIR KAUR
Ph.D. Biotechnology +M.Phil.
Specialization: Molecular biology,
yeast genetics, Translation Regulation

2. What is translation?
The synthesis of protein molecules using mRNA as the template, in other word,
to translate the nucleotide sequence of mRNA into the amino acid sequence of
protein according to the genetic codon.
DNA
mRNA
Protein
Transcription
Translation

3. 1 . Initiation
2 . Elongation
3 . Termination
Steps of translation

4. 1. Initiation
• Complex and large process
Components:
• It require 12 initiation factor ( eIF2, eIF3a, eIF1, eIF1A, eIF5, eIF4A,
eIF4E,eIF4G, eIF4B, eIF5B, eIF2B, eIF6)
• Met-tRNAi
Met
• mRNA
• 40S small ribosome subunit

5. Steps of translation initiation
1.Formation of ternary complex (TC) :eIF2.GTP
binds to initiator Met-tRNAi
Met
2. Formation of 43S Pre -Initiation Complex
(PIC):eIF1+eIF1A+eIF5+eIF3 initiation factors
binds to 40S ribosome and help in recruitment of
TC to 40S subunit of ribosome
eIF2
Met-tRNAi
Met
40S
Met-tRNAi
Met
Alan G. Hinnebusch, 2017

6. Steps of translation initiation
3. Activation mRNA: mRNA activated by
eIF4E+eIF4B+eIF4A+eIF4G initiation factors binds mRNA and
prepare for its binding with 43S PIC Complex
Alan G. Hinnebusch, 2017

7. Steps of translation initiation
4. mRNA binding with 43S complex : Activated mRNA binds to 43S pre
initiation Complex makes it 43S -mRNA Complex.
Alan G. Hinnebusch, 2017

8. Steps of translation initiation
5 Scanning of mRNA for start codon: 43S Pre initiation Complex Start
scanning of mRNA for the search of AUG start codon and GTP bounded to
eIF2 is hydrolyzed by eIF5 initiation factor.
Alan G. Hinnebusch, 2017

9. Steps of translation initiation
6. AUG recognition: After recognition of AUG start codon by tRNA confirmation
changes occur in complex and factor eIF1and Pi release form complex after that eIF5/eIF2-
GDP dissociate from complex . eIF5B-GTP initiation factor binds to complex provide energy
for the binding of 60S larger ribosome subunit.
Alan G. Hinnebusch, 2017

10. Steps of translation initiation
7. 60S subunit joining: 60S subunit joins to complex and makes it 80
complex . eIF5B,eIF1A initiation factor release from complex.
Alan G. Hinnebusch, 2017

11. 2.Elongation
1.STEP: eEF1α+GTP brought
aminoacyle- tRNA to Ribosome empty
A site binds according to next codon in
mRNA
eEF1α+GDP release from complex and
again activated by elongation factor
eEF1βγ
2. STEP: Polypeptide chain transfer
from P site to new amino acid at A site
and make peptide bond.
3 .STEP: eEF-2 induce translation of
ribosome along the mRNA so that
naked tRNA is ejected form E site and
peptidyl-tRNA moves to P site leaving
the A site empty and residing over the
next codon of mRNA.
This process is continue till a stop
codon is encountered .
Peptidyl transfer
Step 2
Peptide bond
formation
Ribosome A site
waiting for new
aminoacyl tRNA
Incoming
aminoacyl-
tRNA+eEF-1α
Elongation
cycle
eEF1α+GDP
release from
complex
GDP
exchange
factor
eEF1βγ
Translocation

12. 3.Termination
1 eRF1 (eukaryotic release factor) recognizes all stop
codons (UAG,UAA,UGA).
2. Other eRF3 release factors bind to A site with bounded
GTP and leads to peptidyl transferase activity and empty
tRNA release from complex
3 inactive ribosome then releases its mRNA and dissociate
itself into subunits.