1. Stages and mechanisms of translation, regulation of translation. Antibiotics – ingibitors of transcription and translation

2. STAGES OF TRANSLATION 1. Recognition 2. Initiation 3. Elongation 4. Termination

3. Aminoacyladenilate RECOGNITION Aminoacyl-tRNA-synthetase Aminoacyladenilate + tRNA  aminoacyl-tRNA + AMP

4. Activation of amino acids Each amino acid has a specific tRNA There is specific aminoacyl-tRNA-synthetase for each AA

5. The structure of tRNA

6. Initiation of Translation The translation complex is assembled at the beginning of the mRNA coding sequence Complex consists of: -Ribosomal subunits -mRNA template to be translated -Initiator tRNA molecule -Protein initiation factors

7. Initiator tRNA First codon translated is usually AUG The initiator tRNA recognizes initiation codons -Bacteria: N-formylmethionyl-tRNA -Eukaryotes: methionyl-tRNA

8. Initiation of protein bio- synthesis Methionyl- тRNA binds to P- center

9. Sites for tRNA binding in ribosomes There are two centers: peptidyl (P) and aminoacyl (А)

10. Elongation 1) Positioning of the next aminoacyl-tRNA in the A site 2) Formation of the peptide bound (enzyme – peptidyl transferase) between methionine and AA in A- centre. The residue of methionine is transferred on the amino group of another AA 3) Translocation – shift of ribosome by one codon. Methionyl-tRNA is released from P-centre. Dipeptidyl- tRNA moves from A-centre to P-centre.

11. Termination of Translation Ribosome comes to terminal codon UGA, UAG or UAA No tRNA molecules recognize these codons and protein synthesis stalls Protein termination factors F-1, RF-2, RF-3 split off synthesized polypeptide from the last tRNA Ribosomal complex dissociates

12. Termina- tion of Trans- lation

13. POSTTRANSLATIONAL MODIFICATION 1)Preparing of proteins for different functions 2)Direction of proteins to different locations (targeting) 1.Removing of methionine (formylmethionine) 2.Formation of disulfide and other bonds (secondary, tertiary structures) 3. Proteolytic cleavage 4. Modification of amino acid residues: - Hydroxylation - Glycosilation - Phosphorilation 5. Joining of prosthetic groups or cofactors 6. Formation of the quaternary structure

14. Regulation of the Protein Biosynthesis The operon model (by Jacob and Monod)

15. Inhibitors of Transcription

16. Antibiotics inhibiting protein synthesis