2. Protein Biosynthesis -2 By Amr S. Moustafa, M.D.; Ph.D.

5. Polyribosome (Polysomes) Several ribosomes and one mRNA

6. Protein Targeting Free Vs attached ribosomes Localization signals

7. Regulation of Translation The dephosphorylated eIF: Active form Heme prevents eIF phosphorylation Heme stimulates translation Proteins/mRNA interactions: e.g., Ferritin and transferrin receptor synthesis

8. Posttranslational Modifications  Trimming  Covalent modifications: PhosphorylationBiotinylation GlycosylationFarnesylation HydroxylationAcetylation Carboxylation  Ubiquitination

9. Posttranslational Modifications: Trimming  Removal of a part of the translated sequence  Proteases protein activation  Cellular site of cleavage: ER and Golgi apparatus Secretory vesicles: e.g., insulin After secretion: e.g., collagen At sites of action: zymogen e.g., trypsinogen

10. Posttranslational Modifications: Phosphorylation Addition of phosphate to hydroxyl group of Serine and threonine Tyrosine Reversible: Addition by kinases Removal by phosphatases Increase or decrease the activity of a specific protein e.g., Glycogen synthase and glycogen phosphorylase

11. Posttranslational Modifications: Phosphorylation

12. Posttranslational Modifications: Glycosylation Modifications of : proteins of plasma membrane proteins of lysosome secretory proteins Addition of carbohydrate chains to: Hydroxyl group of serine or threonine (O-linked) Amide group of asparagine (N-linked) Site: Golgi apparatus and ER Protein targeting: e.g., mannose-6-phosphate to lysosomal enzymes

13. Posttranslational Modifications: Glycosylation

14. Posttranslational Modifications: Hydroxylation Proline and lysine Endoplasmic reticulum Prolyl or lysyl hydroxylases e.g., Collagen

15. Posttranslational Modifications: Other Covalent Alterations - 1 Carboxylation: γ-carboxylation of glutamic acid residue for maturation of vitamin K-dependent clotting factors II, VII, IX and X

16. Carboxylation

17. Posttranslational Modifications: Other Covalent Alterations - 2 Biotinylation Farnesylation e.g., Acetyl Co-A Carboxylase e.g., Protein anchoring to membranes

18. Posttranslational Modifications: Ubiquitination Proteins: Defective Rapid turnover Ubiquitin: Small, highly conserved protein Proteasome: Complex proteolytic system ATP-dependent Cytosol