Translation involves translating the sequence of a messenger RNA (mRNA) molecule to a sequence of amino acids during protein synthesis. It is the process in which ribosomes in the cytoplasm or ER synthesize proteins after the process of transcription of DNA to RNA.

1. TRANSLATION
IN
PROKARYOTES
Dr. Priya Trivedi
M.Sc.(BOTANY), M.Ed., Ph.D.(BOTANY)
Asst.Prof.
at
Compfeeder Aisect College of Professional Studies, Indore

2. L
pl
L
pl

3. Requirement of translation :-
1. m RNA
2. t RNA
3. Ribosome
4. Accessory protein
Initiation factors – IF1, IF2 , IF3.
Elongation factors – Ef-tu, Ef-ts, Ef-G.
Termination factors – RF1, RF2, RF3.
5. Energy requirement – From GTP & ATP
hydrolysis.
GTP – Ribosome movement , binding of
accessory factors.
ATP – Charging of t RNA & removing secondary
structure from m RNA .

5. The actual process of protein synthesis occur in
the following steps : -

6. STEP I.
 Activation of amino acid using ATP : -
(a) Amino acid + ATP + Enzyme Aminoacid – ATP – Enzyme complex
(b) Aminoacid – ATP – Enzyme Amino – acyl – AMP – Enzyme complex
comlpex + p p
STEP II.
 Amino acid binds to its respective t RNA :-
Amino acyl – AMP – Enzyme complex AMP + E
t RNA Aminoacyl – t RNA

7. (Formation of Polypeptide Chain)

9. Binding of small ribosomal subunit (30s) with m
RNA.
 Small ribosomal sub unit which is loaded with
IF1, IF3 , & IF2 complex & GTP binds to
Shine – Dalgarno sequence (5’ – AGGAGGU – 3 ’)
at 5’ end of mRNA.
 Small subunit migrates downstream in 3’ direction
to find out AUG, the initiation codon. It codes for
amino acid methionine.

10. Binding of formylated methionine t RNA to AUG
codon. IF3 is released . It is called initiation compex.
Association of large ribosomal subunit with initiation
Complex.
F1 & IF2 are released & GTP is hydrolysied to GDP.

11. IF
3
IF
1
IF
3
IF
2
IF
1
IF
2
IF
3
IF
1
IF
2
IF
1
GTP
GTP
MET
GTP
GTP
MET
IF
2
5’
5’
3’
3’
mRNA
mRNA

13. P site containing
charged t RNA
Empty A site
aa – tRNA/GTP/Ef-Tu comlpex
Charged tRNA
binds to A site

14. aa – tRNA/GTP/Ef-Tu comlpex
Charged tRNA
binds to A site
Ef – Tu/GDP complex
Peptidyl transferase
( reaction is catalyzed by a
complex enzyme )
tRNA deacylase
( breaks the link between
methionine and its t RNA )

15. Ef – Tu/GDP complex
Peptidyl transferase
tRNA deacylase
Ef – G/GTP complex
Translocation
(Ribosome moves to next
codon)

16. Ef – G/GTP complex
Translocation
GDP

17. ELONGATION
The complex ribosome contains 2 binding sites
positioned to 2 codons of m RNA.
These are :-
• P- site (peptidyl site)
•A- site (aminoacyl site)
The P – site is positioned to initiation codon AUG
which is occupied by methione t RNA complex &
A – site is empty.
Elongation begins with the entry of another t RNA
carrying aminoacid to A – site . Anticodon of this
t RNA should base pair with 2nd codon .

18. When both sites are occupied with charged t RNA,
two aminoacid are placed in close contact & a
peptide bond is formed between carboxyl group of
methionine & amino group of second amino acid.
The reaction is catalysed by enzyme peptidyl
Transfarase.
Another enzyme t RNA deacylase breaks the link
between methionine & its t RNA after formation of
peptide bond.

19. Some accessory proteins called elongation factors
( Ef ) are required for elongation process.
These are – Ef – Tu & Ef – Ts.
Ef – Tu is associated with entry of t RNA into
A – site. It binds charged t RNA in association with
GTP.
Following entry to A – site GTP is hydrolysised &
Ef – Tu is released bound to GDP .
Ef – Ts is regenerated with the help of Ef – Ts .
Ef – Ts binds Ef – Tu displacing GDP & then new
GTP molecule replace Ef – Ts .

20. Ef – Ts is regenerated with the help of Ef – Ts.
Ef – Ts binds Ef – Tu displacing GDP & then
new GTP molecule replace Ef – Ts.
Following peptide bond formation Translocation
occurs & ribosome moves to the next codon.
The newly formed dipeptide bound to 2nd t RNA
Moves to P – site expelling the uncharged t RNA
& the site A becomes vacant.

21. Now a third charged t RNA enters the A – site &
Elongated cycle is repeated .
In this way ribosome translocates towards the 3’ end
transcribing m RNA .
The free 5’ end of m RNA is occupied successively
by another ribosomal units.
The structure thus formed is called polysome /
polyribosome.

23. Termination
Translation ends when a termination codon enters the
A – site. There are no tRNA to bind the termination
Codons. Instead of t RNA some protein called
release factor (RF) enter the A – site & cause the
completed polypeptide to be released.
In bacteria Rf – 1 & Rf – 2 perform this function .
Rf – 1 recognizes UAA & UAG stop signals.
Rf – 2 recognizes UAA & UGA.
Rf – 3 plays an ancillary role in the process.

24. RF1 OR 2, RF3
TERMINATION
CODON

25. H2O Peptidyltransferase

26. m RNA is released
ribosome dissociates
t RNA RF1/2 , RF3

27. small
subunit
LARGE
SUBUNIT
m RNA is released
ribosome dissociates
t RNA RF1/2 , RF3