Translation In Eukaryotes

An Overview...
Definition of Translation.
Def. of Eukaryotes.
Translation: An Overview.
Components of Translation.
Some Enzymes .
Ribosome Role.
Mechanism of Translation.
Initiation.
Scanning Model of Initiation.
Initiation Factors.
Animation.
Elongation.
Chain Elongation: Translocation.
Animation.
Termination.
Animation....

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1. Translation In Eukaryotes Muhammad Umer Farooq BAGF13E221

2. What Is Translation?? Translation is the process by which protein is synthesized from the information contained in a molecule of messenger RNA (mRNA).

3. What are Eukaryotes? E ukaryotes are organisms with a complex cell or cells, in which the genetic material is organized into a membrane-bound nucleus or nuclei and it also contains cell organelles.

4. Translation: An Overview Ribosomes translate the genetic message of mRNA into proteins. The mRNA is translated from 5 ’ 3’. Amino acids bound to tRNAs are inserted in a proper sequence due to: - Specific binding of each amino acid to its tRNA. - Specific base-pairing between the mRNA codon and tRNA anticodon.

5. Components of Translation mRNA: - Made in the nucleus, transported to cytoplasm. tRNA: - Adaptor molecule that mediate the transfer of information from nucleic acid to protein. Ribosomes: - Manufacturing units of a cell. Enzymes: - Required for the attachment of amino acids to the correct tRNA molecule, and for peptide bond formation between amino acids. Proteins: - Soluble factors necessary for proper initiation, elongation and termination.

6. Enzymes catalyze the attachment of tRNA molecule to its respective amino acid . - At least one for each tRNA. - Attachment of amino acid activates/ charges the tRNA molecule. catalyzes the sequential transfer of amino acid to the growing chain. - Forms the peptide bond between the amino acids. Aminoacyl-tRNA Synthetases Peptidyl Transferase

7. Ribosomes: Role In Translation The smaller subunit is the one that initially binds with the mRNA. The larger subunit provides the enzyme activity: - Peptidyl transferase - Catalyzes the formation of peptide bonds joining amino acids. The assembled structure of ribosome creates three pockets for the binding of two molecules of tRNA. - A site - P site - E site

8. Mechanism O f Translation Three steps of translation: - Initiation: Sets the stage for polypeptide synthesis . - Elongation: Causes the sequential addition of amino acids to the polypeptide chain as determined by mRNA. - Termination: Brings the polypeptide synthesis to the halt.

9. Initiation The initiation codon is an AUG. - is towards the 5 ’ end of the mRNA molecule that Is being translated.

10. Scanning Model of Initiation Proposed by M. Kozak Small subunit of ribosome (+ initiation factors , GTP and tRNAi Met ) binds to the 5’ Cap, and scans along the mRNA until the first AUG Translation starts at the first AUG

11. Initiation Factors eIF-1(and 1A) : promotes scanning. * eIF-2: binds tRNAi Met to 40S subunit, requires GTP (which gets hydrolyzed to GDP) eIF-2B : catalyzes exchange of GTP to GDP on eIF-2 *eIF-3 : binds to 40S subunit, prevents 60S subunit from binding to it eIF-5 : stimulates 60S subunit binding to the 40S pre-initiation complex *eIF-6 : binds to 60S subunit, helps prevent 40S subunit from binding to it

12. Elongation At the start of elongation, the mRNA is bound to the complete two subunit ribosome, - With the initiating tRNA in the P site, - and the A site is free for binding to the next tRNA. The ribosome moves along the mRNA in a 5’ to 3 ’ direction, in a step-wise process, recognizing each subsequent codon. The peptidyl transferase enzyme then catalyzes the formation of a peptide bond between - the free N terminal of the amino acid at the A site, - and the Carboxyl end of the amino acid at the P site, which is actually connected to the tRNA . This disconnects the tRNA fMet from the amino acid, and the tRNA at the A site now carries two amino acids, - with a free N terminal and the Carboxyl terminal of the second amino acid connected to its tRNA.

13. Chain Elongation: Translocation During translocation the peptidyl-tRNA remains attached to its codon, but is transferred from the ribosomal A site to the P site. The vacant A site now contains a new codon, and an aminoacyl-tRNA with the correct anticodon can enter and bind . The process repeats until a stop codon is reached .

14. Chain Elongation: Translocation In both prokaryotes and eukaryotes, simultaneous translation occurs . - New ribosomes may initiate as soon as the previous ribosome has moved away from the initiation site, creating a polyribosome (polysome). - An average mRNA might have 8–10 ribosomes attached at a given moment.

15. Termination When the ribosome encounters a stop codon , - there is no tRNA available to bind to the A site of the ribosome, - instead a release factor binds to it . The details are not very clear, but once the release factor binds, the ribosome unit falls apart , - releasing the large and small subunits, - the tRNA carrying the polypeptide is also released, freeing up the polypeptide product .