Introduction Definition History central dogma Major components mRNA,tRNA,rRNA Energy source Amino acids Protien factor Enzymes Inorganic ions Step involves in translation: Aminoacylation of tRNA Initiation Elongation termination Importance of translation Conclusion Reference

1. TRANSLATION CYCLE
By
KAUSHAL KUMAR SAHU
Assistant Professor (Ad Hoc)
Department of Biotechnology
Govt. Digvijay Autonomous P. G. College
Raj-Nandgaon ( C. G. )

2. SYNOPSIS
Introduction
Definition
History
central dogma
Major components
mRNA,tRNA,rRNA
Energy source
Amino acids
Protien factor
Enzymes
Inorganic ions

3. Step involves in translation:
Aminoacylation of tRNA
Initiation
Elongation
termination
Importance of translation
Conclusion
Reference

4.  Biosynthesis of protein is under direct control of
DNA in most cases or under control of genetic
RNA where DNA is absent.
 It proceed from 5’-3’ direction. The direction of
growth of polypeptide chain starting from amino
terminal to carboxyl terminal.

5. “Transfer of language of nucleic acid
into the language of protein is called
translation”.

6. History
Crick [1958] proposed relationship
between DNA, RNA & Protien.
Central Dogma
Relationship between
DNA,RNA & protein is called central dogma.

7.  1,Ribosome: The ribosome are ribonucleoproteins
made up of RNA & protein. The ribosomal proteins are
called r-protein.
Prokaryotes: 70S 50S ,30S
Eukaryotes: 80S 60S,40S

8. 1. mRNA binding site.
2.A (amino acyl site): incoming amino acid carrying t RNA
binds.
3. P(peptidyl site) : the tRNA carrying the growing
polypeptide chain residues.
4. E (exit site) : From which tRNA leave the ribosome after
they are discharge their amino acid.

9. The amino acids themselves are unable to recognize
different nucleotide codon along the mRNA Template, they
must be brought to the correct codon by Other molecule
termed as adapter.
Appropriate to these adaptor , tRNA molecules have
two kinds of specicality:
Each tRNA molecules reconizes a specific codon on
mRNA.
Each caries an amino acid that is specially chosen
to that codon according to the dictates of
genetic code.

10. Fig. structure of

11. The heart of mRNA is its message the sequence of nucleotide
that encodes a polypeptide.
Procaryotic mRNA does not require modifications while
eukaryotes mRNA have several modifiication steps.
Translation does not simply begins at the 5’ end of mRNA ; it
starts at specific initiation site. Therefore the 5’ terminal of both
prokaryote and eucaryote have non-coding sequences called
untranslated region.
Eucaryotic mRNAs usually encod only a single polypeptide chain,
but many procaryotes encode multiple polypeptides that are
synthesiized independently from distinct initiation sites.

12. mRNA that encode multiple polypeptides are called
polycistronic whereas monocistronic mRNAs encode a
single polypeptide chain. Finally, both prokartotic and
eucaryotic mRNAs end in noncoding 3’ untranslted region.
In both procaryotes and eukaryotes, translation
always initiates with the amino acid methiomine,
usually encoded by AUG.
Alternative initiation codons such as GUG are used
occasionally and directs the incorporation of methionine (
normally it encodes valine.)

13. Proteins are polymers of amino acids. 20 amino acids
found in protein structure. Half of them can be
synthesized in the body.
About 10 essential amino aids have to be provided through
the diet.
Protein synthesis occurs only when all the amino acids
needed for a particular proteins are available.
If there is a deficiency in the dietary supply of any one of
the essential amino acids he translation stops.

14. 5. Energy source
Both ATP and GTP are required for the supply
of energy in protien synthesis.
6. Protein factors
The translation steps require protien factor for ex;
Initiation – IFs – atleast 24 protiens
Elongationn- EFs- eEF-1, EFTU
Terminion- RFs-eRF1 ,eRF2, RF1

15. 7. ENZYMES
Several enzymes are also involved in translation
process .
Ex- Aminoacyl t-RNA synthatase.
8. Various inorganic ions
Various inorganic cations are involved in the
process of translation
Ex- K+ ,,Mg+

16. MAJOR
STEPS
Initiation
Elongation
Termination
Aminoacylat
ion of tRNA
TRANSLATION IN PROCARYOTES

17. Formylation of methionine
Protein syntheses beging at the amino terminal end and proceed by
the stepwise addition of amino acids to the carboxyl-terminal end of
the growing polypeptide.
The AUG initiation codon thus specifices an amino-terminal
methionine residue.
The amino acid incorporated in response to the (5’) AUG initiation
codon is N-formyl-methionine (fMet).
It arrives at the ribosome as N-formylmethionyl-tRNAfMet (fMet-
tRNAfMet), which is formed in two successive reactions.

18. First, methionine is attached to tRNAfMet by the
Met-tRNA synthetase:
Methionine + tRNA-fMet + ATP Met-tRNA-
fMet + amp
+ PPi
Next, a transformylase transfer a formyl group from N10_
Formyltetrahydrofolateto the amino group of the Met
residue:
N10-Formyltetrahydrofolate + Met-tRNAfMet
tetrahydrofolate + fMet-tRNAfMet

19. Aminoacylation of t-RNA
This process is completed in 2 steps:
(a) Activation of amino acid
Amino acid + ATP Aminocyl t-RNA sythetase
Aminoacyl –AMP + Pi
(b) Transfer of activated amino acid to t-RNA
Amino acyl –AMP + tRNA Aminoacyl t-RNA synthetase
Aminoacyl tRNA + AMP

20. Initiation
Initiation requires a large and small ribosomal subunit , a
molecule of mRNA, a set of proteins known as initiation factors,
GTP (for energy), and an initiator tRNA.
The initiator tRNA has UAC for its anticodon, to allow it to base
pair with the AUG start codon. It is charged with a special amino
acid, formyl methionine, or fmet for short.
The initiation of polypeptide synthesis in bacteria required 7
components;
30S ribosomal subunit ,mRNA,50S ribosomal subunit , 3 proteins
are called initiation factors (IF1,IF2,IF3) & Mg2+

21. IF1 : stimulates the activity of IF2 & IF3..
Prevents premature binding of tRNAs to A site..
IF2 : Facilitates binding of fMet-tRNA fmet to
30S ribosomal subunit.
IF3 : Binds to 30S subunits; prevents premature
association of 50S subunit; enhances specificity for
P-site for fmet-tRNA fmet

22. 1. The small ribosomal subunit binds to Initiation Factor 3 (IF3).
2. The small subunit/IF3 complex binds to the mRNA.Specifically,it
binds to the sequence AGGAGG, known as the Shine-Delgarno
sequence, which is found in all prokaryotic mRNAs
Initiation process

23. 3. Meanwhile, the fmet tRNA binds to codon. Initiation Factor 2
(IF2), which promotes binding of the tRNA to the start
4. The small subunit/IF3 complex scans along the mRNA until it
encounters the start codon. The tRNA/IF2 complex also binds to the
start codon. This complex of the small ribosomal subunit, IF3, initiator
tRNA, and IF2 is called the initiation complex

24. At this point, the large ribosomal subunit joins in. A
molecule of GTP is hydrolyzed, and the initiation factors are
released. The ribosomal complex is now ready for protein
synthesis.

25. Elongation
When the ribosome is assembled,
two tRNA binding sites are created;
these are designated 'P' and 'A'.
The initiator tRNA is in the P
site, and the A site will be filled by
the tRNA with the anticodon that
is complementary to the codon next
to the start.

26. When the second tRNA base
pairs with the appropriate
codon in the mRNA, an
enzyme called peptidyl
transferase catalyzes the
formation of a peptide
bond between the two
amino acids present (while
breaking the bond between
fmet and its tRNA).

27. At this point, the whole
ribosome shifts over one codon.
This shift requires several
elongation factors and energy
from the hydrolysis of GTP.
The result of the shift is that
the uncharged tRNA that was
in the P site is ejected, and the
tRNA that was in the A site is
now in the P site.
The A site is free to accept the
tRNA molecule with the
appropriate anticodon for the
next codon in the mRNA.

28. The next tRNA base
pairs with the next
codon, and peptidyl
transferase catalyzes
the formation of a
peptide bond between
the new amino acid and
the growing peptide
chain

29. Once again, the ribosome shifts over,
so that the uncharged tRNA is
expelled, and the tRNA with the
peptide chain occupies the P site.
The process of shifting and peptide
bond formation continues over and
over until a termination codon is
encountered.
The elongation process is fairly rapid,
with prokaryotic ribosomes able to
add 15 amino acids to the growing
polypeptide every second.

30. ermination
When a termination codon
enters the A site,
translation halts. This is
because there is no tRNA
with an anticodon that is
complementary to any of
the stop codons.

31. The termination codon is
recognized and bound to
by a release factor. The
release factor is a
protein, like the
initiation factors and
the elongation facotrs,
that is independent of
the ribosome.

32. The release factor causes
the translation complex to
fall apart, and cleaves the
polypeptide from the final
tRNA.
The polypeptide product is
now free to function in the
cell.
The mRNA molecule is
now available to be
translated again.

33. Very often, more than one ribosome will translate a
single mRNA at the same time.
One ribosome will initiate translation, and after it
moves down the mRNA a bit, another ribosome will
initiate, then another, and so on.
The structure consisting of multiple ribosomes
translating a single mRNA molecule is called a
polysome. Eventually, the mRNA is degraded, and
translation of that particular message will cease.

34. Eukaryotic translation
Eukaryotic translation is the process by which messenger RNA is translated into
proteins in eukaryotes.]
Initiation

35. The Steps of Translation

36. Initiation
The small subunit of the ribosome binds to a site
"upstream" (on the 5' side) of the start of the message.
It proceeds downstream (5' -> 3') until it encounters
the start codon AUG.
Here it is joined by the large subunit and a special
initiator tRNA.
The initiator tRNA binds to the P site on the
ribosome.

37.  An aminoacyl-tRNA able to base pair with the next
codon on the mRNA arrives at the A site associated
with:
an elongation factor (called EF-Tu in bacteria;
EF-1 in eukaryotes)
GTP (the source of the needed energy)
 The preceding amino acid (Met at the start of
translation) is covalently linked to the incoming
amino acid with a peptide bond .

38. The end of translation occurs when the ribosome
reaches one or more STOP codons (UAA, UAG,
UGA).
The nucleotides from this point to the poly(A) tail
make up the 3'-untranslated region [3'-UTR] of the
mRNA.
There are no tRNA molecules with anticodons for
STOP codons.

39. Differences
Remember that only eukaryotes, and not
prokaryotes, underwent post- transcriptional RNA
modifications.
Whereas prokaryotic initiation, which have just
covered, begins with the ribosomal recognition of the
ribosome binding site on the mRNA, eukaryotic
initiation begins with the ribosomal recognition of
the 5' cap.

40. Eukaryotic mRNA neednot contain a ribosome
binding cap because the post-transcriptionally added
5' cap suffices for recognition.
Once the eukaryote ribosome binds to the mRNA,
further differences appear. Whereas in prokaryotes
the initiator codon can be either GUG or AUG, in
eukaryotes the codon must be AUG.
Additionally, the tRNA responsible for
recognizing the initiator codon is not the special
tRNA, fMet, but rather the normal met-tRNA

41. Fig. Translation overview

42. S.N
o.
AUTHOR BOOK
1. Geoffrey M.Cooper The Cell
2. Lehninger (Nelson & Cox ) Principle of Biochemistry
3. P.K. Gupta Molecular Biology
4. C. B Powar Cell Biology
Website:
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