1. Protein Synthesis and Controlled Protein Breakdown
Chapter 24
Protein Synthesis and Controlled Protein Breakdown

2. Chapter Objectives
Know the process of protein synthesis and the genetic code (don’t memorize the genetic code)
Know how ribosomes work
Initiation, elongation, termination
Know the key steps in protein folding
Understand how protein translation is controlled
Know the process of protein degradation

3. The Genetic Code Nonsense mutation – stop codon
Degenerate code – more than one codon per amino acid
Conservation

4. Overview of Protein Synthesis
Amino acids are activated by aminoacyl synthetases using ATP
Amino acids are added to tRNA
tRNA molecules with their attached amino acid are brought to ribosome
The growing peptide chain is added to each new amino acid
Energy cost = 1 ATP & 2 GTP

5. tRNA
There are not 61 different tRNA molecules

6. tRNA Wobble Wobble allows for less tRNA molecules to be needed
Notice orientation!!

7. Amino Acid Attachment to tRNA
Must attach correct amino acid to tRNA
Wrong amino acid will be incorporated into protein otherwise
Specific aminoacyl-tRNA synthetase for each tRNA / amino acid pair
Need 20!
No consistent recognition
Sometimes anticodon
Sometimes other regions of tRNA
Always side chain of amino acid
Process driven by ATP hydrolysis

8. Specificity of Amino Acid Priming

9. Ribosomes Prokaryote ribosomes Subunits Total
23S and 5S pieces of RNA and 34 proteins
16 S piece of RNA and 21 proteins
Total
50S (large subunit)
30S (small subunit)

11. Translation Initiation
30S ribosome subunit binds to Shine-Dalgarno sequence placing AUG in P site
Special met-tRNA recognizes IF2 (initiation protein factor 2)
IF3 prevents binding of 50S subunit prematurely
Shine-Dalgarno
50S subunit then associates
IF2&3 are displaced
GTP is hydrolyzed

12. Elongation

13. Termination This picture is from eukaryotes
Think of 60S as 50S and 40S as 30S
RF1 and 3 are RF1 and 2 in prokaryotes
Still need to bring in IF3 to prevent interaction of 30S with 50S

14. Overview

15. Better overview

16. Drugs that inhibit Translation
Chloramphenicol – peptidyl transferase
Erythromycin – 50S inhibits translocation
Kirromycin or fusidic acid – prevents EF-Tu release
Sparsomycin –peptidyl transferase inhibitor
Streptomycin – initiation misread
Tetracyclin – inhibits tRNA from binding ribosome

17. Riboswitches

18. Selenocysteine Not a standard amino acid
Made from cysteine and selenium (toxic)
Uses UGA stop codon with special tRNA and EF
Rare

19. Protein Folding Chaperones Protein Disulfide Isomerases (PDI)
ATP dependant
Heat Shock proteins
Protein Disulfide Isomerases (PDI)
Peptidyl proline isomerase (PPI)

20. GroEL GroES chaperone

21. Prion Proteins

22. Programmed Protein Death
Proteasome
Ubiquitin
Poly
Mono

23. Ubiquitin Pathway E1 is ubiquitin activating enzyme (ATP needed
E2 accepts Ub
E3 ligase activity
Multiple E2/E3 combos