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Lesson 3: Translation. From RNA to protein: translation The genetic code Three possible “reading frames” THE ABC FOR THE DNA THE AXB CFO RTH EDN A THE.

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Presentation on theme: "Lesson 3: Translation. From RNA to protein: translation The genetic code Three possible “reading frames” THE ABC FOR THE DNA THE AXB CFO RTH EDN A THE."— Presentation transcript:

1 Lesson 3: Translation

2 From RNA to protein: translation The genetic code Three possible “reading frames” THE ABC FOR THE DNA THE AXB CFO RTH EDN A THE ACF ORT HED NA Insertion (X) or Deletion (B)

3 Ribosomes in the cytoplasm of a eukaryotic cell

4 Composition of eukaryotic ribosomes

5 RNA-binding sites in the ribosome Each ribosome has: a binding site for mRNA three binding sites for tRNA A-site: aminoacyl-tRNA P-site: peptidyl-tRNA E-site: exit

6 tRNA molecules: matching amino acids to codons in mRNA

7 Translation of the genetic code: two adaptors that act one after another

8 mRNA translation mechanism Step1:An aminoacyl-tRNA molecule binds to the A-site on the ribosome Step2:A new peptide bond is formed Step3:The small subunit moves a distance of three nucleotides along the mRNA chain ejecting the spent tRNA molecule Step4:The next aminoacyl-tRNA molecule binds to the A-site on the ribosome Step5:...

9 The initiation phase of protein synthesis in eukaryotes 1.Initiation complex (small ribosomal subunit + initiation factors) binds DNA and searches for start codon 2.Large ribosomal subunit adds to the complex 3.Translation starts 4....

10 Prokaryotic vs eukaryotic mRNA molecules

11 Structure of a typical prokaryotic mRNA molecule

12 5´ end capping of eukaryotic mRNA molecules

13 The final phase of protein synthesis  binding of release factor to a stop codon terminates translation  the completed polypeptide is released  the ribosome dissociates into its two separate subunits

14 Polyribosomes: several ribosomes can simultaneously translate the same mRNA molecule

15 Proteasomes : degradation of “unwanted” proteins in eukaryotic cells

16 The production of a protein by a eukaryotic cell Many levels of regulation/variation

17 Protein import by membrane-bounded organelles ATP !!!

18 The role of signal sequences in protein sorting proteins destined for the ER: N-terminal signal sequence that directs them proteins destined to remain in the cytosol: no signal sequence

19 Free and membrane-bound ribosomes

20 ER signal sequence and SRP: directing ribosomes to the ER membrane

21 Translocation of a soluble protein across the ER membrane

22 Integration of a transmembrane protein into the ER membrane

23 Integration of a double-pass transmembrane protein into the ER membrane

24 Vesicular traffic

25 Clathrin-coated pits and vesicles

26 Selective transport: mediated by clathrin-coated vesicles

27 Model of transport vesicle docking

28 Transport vesicle fusion

29 Protein glycosylation in the ER

30 The Golgi apparatus

31 Exocytosis: the regulated and constitutive pathways

32 Exocytosis of secretory vesicles


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