PROTEIN METABOLISM

1. PROTEIN METABOLISM Obviously, Harry [Noller]’s finding doesn’t speak to how life started, and it doesn’t explain what came before RNA. But as part of the continually growing body of circumstantial evidence that there was a life form before us on this planet, from which we emerged—boy, it’s very strong! —Francis H. C. Crick, article in Symposia of the Society for Experimental Biology, 1958

2. The Genetic Code

3. Ribosomes and endoplasmic reticulum

4. Overlapping versus nonoverlapping genetic codes

5. ”Dictionary” of amino acid code words in mRNAs

6. the Genetic Code

7. How the Wobble Base of theAnticodon Determines the Number of Codons atRNA Can Recognize

8. Protein Synthesis • Protein Biosynthesis Takes Place in Five Stages; • Stage 1: Activation of Amino Acids • Stage 2: Initiation • Stage 3: Elongation • Stage 4: Termination and Release • Stage 5: Folding and Posttranslational Processing

10. The Ribosome Is a Complex Supramolecular Machine

11. The Ribosome Is a Complex Supramolecular Machine

12. RNA and Protein Components of the E. coli Ribosome

14. Bacterial rRNAs

15. Transfer RNAs Have CharacteristicStructural Features

16. Three-dimensional structure of yeast tRNAPhe deduced from x-ray diffraction analysis

17. Stage 1: Aminoacyl-tRNA Synthetases Attach theCorrect Amino Acids to Their tRNAs

18. The Two Classes of AminoacyltRNASynthetases

21. General structure of aminoacyl-tRNAs

22. Proofreading by Aminoacyl-tRNA Synthetases The aminoacylation of tRNA accomplishes two ends: (1) activation of an amino acid for peptide bond formation and (2) attachment of the amino acid to an adaptor tRNA that ensures appropriate placement of the amino acid in a growing polypeptide. The identity of the amino acid attached to a tRNA is not checked on the ribosome, so attachment of the correct amino acid to the tRNA is essential to the fidelity of protein synthesis.

23. Some positions (blue dots) are thesame in all tRNAs and therefore cannot be used to discriminate one from another. Other positions are known recognition points for one (orange) or more (green) aminoacyl-tRNA synthetases. Structural features other than sequence are important for recognition by some of the synthetases.

25. Formation of the initiation complex in bacteria

26. Messenger RNA sequences that serve as signals forinitiation of protein synthesis in bacteria

27. Protein complexes in the formation of a eukaryoticinitiation complex

28. Protein Factors Required for Initiation of Translation in Bacterial and Eukaryotic Cells

29. First elongation step in bacteria: binding of the secondaminoacyl-tRNA

30. Stage 3: Peptide Bonds Are Formed in the Elongation Stage

32. First elongation step in bacteria: binding of the secondaminoacyl-tRNA

33. Second elongation step in bacteria: formation of the first peptide bond

34. Third elongation step in bacteria: translocation

35. Stage 4: Termination of Polypeptide Synthesis Requires a Special Signal

36. Stage 5: Newly Synthesized Polypeptide Chains Undergo Folding and Processing (Coupling of transcription and translation in bacteria.)

37. Polysomes

38. Stage 5: Newly Synthesized Polypeptide Chains Undergo Folding and Processing (posttranslational modifications) • Amino-Terminal and Carboxyl-Terminal Modifications • Loss of Signal Sequences • Modification of Individual Amino Acids • Attachment of Carbohydrate Side Chains • Addition of Isoprenyl Groups • Addition of Prosthetic Groups • Proteolytic Processing • Formation of Disulfide Cross-Links

39. Protein Synthesis Is Inhibited by Many Antibioticsand Toxins

42. Directing eukaryotic proteins with the appropriate signals to the endoplasmicreticulum

43. Synthesis of the core oligosaccharide of glycoproteins

45. Protein Degradation Is Mediated by Specialized Systems in All Cells

46. Three-step cascade pathway by which ubiquitin is attached to a protein

47. Three-dimensional structure of the eukaryotic proteasome