1. Translation Md. Habibur Rahaman (HbR)
Dept. of Biochemistry and Microbiology
North South University

2. Stages of Translation Process
Protein synthesis can be conveniently divided into four stages:
The binding of amino acids to the tRNAs
(2) Initiation, in which the components necessary for translation are assembled at
the ribosome
(3) Elongation, in which amino acids are joined, one at a time, to the growing polypeptide chain
(4) Termination, in which protein synthesis halts at the termination codon and the
translation components are released from the ribosome.

3. The Binding of Amino Acids to Transfer RNAs
Cell typically possesses from 30 to 50 different tRNAs
Collectively, these tRNAs are attached to the 20 different amino acids.
Each tRNA is specific for a particular kind of amino acid.
All tRNAs have the sequence CCA at the 3’ end, and the carboxyl group (COO ) of the amino acid is attached to the 2’- or 3’-hydroxyl group of the adenine nucleotide at the end of the tRNA

4. If each tRNA is specific for a particular amino acid but all amino acids are attached to the same nucleotide (A) at the 3’ end of a tRNA, how does a tRNA link up with its appropriate amino acid?
The key to specificity between an amino acid and its tRNA is a set of enzymes called aminoacyl-tRNA synthetases.
A cell has 20 different aminoacyl-tRNA synthetases, one for each of the 20 amino acids.
Each synthetase recognizes a particular amino acid, as well as all the tRNAs that accept that amino acid.
Recognition of the appropriate amino acid by a synthetase is based on the different sizes, charges, and R groups of the amino acids.

5. The tRNAs, however, are all similar in tertiary structure
The tRNAs, however, are all similar in tertiary structure. How does a synthetase distinguish among tRNAs?
The recognition of tRNAs by a synthetase depends on the differing nucleotide sequences of tRNAs.
Researchers have identified which nucleotides are important in recognition by altering different nucleotides in a particular tRNA and determining whether the altered tRNA is still recognized by its synthetase.
The results of these studies revealed that the anticodon loop, the DHU-loop, and the acceptor stem are particularly critical for the identification of most tRNAs

6. The attachment of a tRNA to its appropriate amino acid (termed tRNA charging) requires energy, which is supplied by adenosine triphosphate (ATP):
This reaction takes place in two steps:
Errors in tRNA charging are rare; they occur in only about 1 in 10,000 to 1 in
100,000 reactions.
This fidelity is due to the presence of proofreading activity in the synthetases, which detects and removes incorrectly paired amino acids from the tRNAs.

8. The Initiation of Translation
Prokaryotic Initiation System
The second stage in the process of protein synthesis is initiation.
During initiation, all the components necessary for protein synthesis assemble:
mRNA
the small and large subunits of the ribosome
a set of three proteins called initiation factors
initiator tRNA with N-formylmethionine attached (fMet-tRNAfMet )
guanosine triphosphate (GTP).
Initiation comprises three major steps.

9. The Initiation of Translation
Prokaryotic Initiation System
Initiation comprises three major steps.
First, mRNA binds to the small subunit of the ribosome.
Second, initiator tRNA binds to the mRNA through base pairing between the codon and anticodon.
Third, the large ribosome joins the initiation complex.

10. The Initiation of Translation
Prokaryotic Initiation System

11. The Initiation of Translation
Prokaryotic Initiation System
The sequence covered by the ribosome during initiation is from 30 to 40 nucleotides long and includes the AUG initiation codon.
Within the ribosome-binding site is the Shine-Dalgarno consensus sequence, which is complementary to a sequence of nucleotides at the 3’ end of 16S rRNA (part of the small subunit of the ribosome).
During initiation, the nucleotides in the Shine-Dalgarno sequence pair with their complementary nucleotides in the 16S rRNA, allowing the small subunit of the ribosome to attach to the mRNA and positioning the ribosome directly over the initiation codon.

12. The Initiation of Translation
Eukaryotic Initiation System
The small subunit of the eukaryotic ribosome, with the help of initiation factors, recognizes the cap and binds there;
the small subunit then migrates along (scans) the mRNA until it locates the first AUG codon.
The identification of the start codon is facilitated by the presence of a consensus sequence (called the Kozak sequence) that surrounds the start codon:

16. Lehninger (5E)

17. Elongation Elongation requires the 70S complex just described
tRNAs charged with their amino acids;
several elongation factors (EF-Ts, EF-Tu, and EF-G);
(4) GTP.
A ribosome has three sites that can be occupied by tRNAs; the aminoacyl, or A site, the peptidyl, or P site, and the exit, or E site

20. Regeneration of EF-Tu-GTP complex
to carry out the elongation
Lehninger (5E)

21. How peptide chain grows?
Lehninger (5E)

22. Termination

23. The Overall Process of Protein Synthesis

24. RNA–RNA Interactions in Translation
(1) The process of translation is rich in RNA–RNA interactions. For example, in bacterial translation, the Shine-Dalgarno consensus sequence at the 5’ end of the mRNA pairs with the 3’ end of the 16S, which ensures the binding of the ribosome to mRNA

26. Polyribosomes
In both prokaryotic and eukaryotic cells, mRNA molecules are translated
simultaneously by multiple ribosomes. The resulting structure—an mRNA with several ribosomes attached—is called a polyribosome.
Each ribosome successively attaches to the ribosome- binding site at the 5’ end of the mRNA and moves toward the 3’ end; the polypeptide associated with each ribosome becomes progressively longer as the ribosome moves along the mRNA.

28. A Comparison of Bacterial and Eukaryotic Translation
Initiator Amino Acid
Temporal and Spatial Differences of Gene Expression
Longevity of mRNA
Sizes and Compositions Ribosomal Subunits
Initiation of Translation
Elongation and Termination

30. The Posttranslational Modifications of Proteins

31. Translation and Antibiotics

32. Disruption of peptide bond formation by puromycin.

33. Thank you all… Good Luck for final
Thank you all… Good Luck for final! Stay very best and shine like stars….