molecular biology

2. Translation
Presented by-
Sonam Sneha
M.Sc.-Ph.D-Biotech Ist yr
IIIrd trimester

3. Contents
• Introduction
• Components of translation
• Stages of translation
i Activation of amino acid
ii Initiation
iii Elongation
iv Termination
• References

4. Introduction
• In translation, messenger RNA (mRNA produced
by transcription )is decoded by the ribosome to
produce a specific amino acid chain, or polypeptide,
that will later fold into an active protein.
• Occurs in the cell's cytoplasm, where the large and
small subunits of the ribosome are located, and
bind to the mRNA.
• Direction of translation is 5’ to 3’.
• There are 4 stages in the translation-

6. Key components in translation
• The ribosome, and
• t- RNA

7. STAGES OF TRANSLATION

8. Activation of amino acid
• Occurs in cytosol
• Aminoacyl-tRNA synthetases esterify the 20
amino acids to their corresponding tRNAs.
• The reaction-
Amino acid +tRNA +ATP aminoacyl-tRNA + AMP+PPi

10. Mechanism of aminoacylation of tRNA
by aminoacyl-tRNA synthetase
• Step 1-formation of an aminoacyl adenylate
which remain bound to the active site.
• Step 2-aminoacyl group is transferred to
tRNA,two classes of aminoacyl-tRNA
synthetase classI and classII
• Step 3- transesterification in case of class I
enzyme.

12. Initiation
• 5’AUG is the initiation codon for protein
synthesis.
• In bacteria 2 types of tRNA specific for
methionine are designated tRNAMet and
tRNAfMet.
• Methionine +tRNAMet +ATP Met-tRNAfMet + AMP + PPi
N10 Formyltetrahydrofolate + Met-tRNAfMet tetrahydrofolate +fMet- tRNAfMet

13. Steps of initiation
• Requirements-
30s ribosomal subunit ,
mRNA ,
initiating fMet- tRNAfMet ,
initiation factor (IF-1,IF-2,IF-3),
GTP,
50s ribosomal subunit and Mg2+ .
• Three steps-(see in fig.)

15. IF1 and IF3 bind to a free 30S subunits.
IF2 complexed with GTP then bind to
the small subunits, forming a complex at
RBS.
The initiator tRNA can then bind to the
complex at the P site paired with AUG
codon.
The 50S subunits can now bind. GTP is
then hydrolyzed and IFs are released to
give the 70S initiation complex
30S initiation complex

16. Elongation-formation of peptide bonds
• Requirements-
Initiation complex
Aminoacyl tRNAs
A set of 3 soluble cytosolic proteins called
elongation factors(EF-Tu,EF-Ts,and EF-G).
GTP.

17. Steps in elongation
• Step 1-Binding of an incoming Aminoacyl-
tRNA.
• Step 2-Peptide bond formation
• Step 3-Translocation

20. Termination
• Signaled by the presence of one of three
termination codons in the mRNA
(UAA,UAG,UGA) ,immediately following the
final coded amino acid.
• Once a termination codon occupies the
ribosomal A-site, three termination factors or
release factors , the proteins RF-1,RF-2, and
RF-3.

22. References
• http://www.mun.ca/biology/desmid/brian/BIOL2060/BIOL20
60-22/2208.jpg&imgrefurl
• MichaelM.Cox,David,Nelson(2008),lEHNINGER’s Principles
Of Biochemistry, 5th Edition; W H Freeman and company,pg-