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Chapter 24 Protein Synthesis and Controlled Protein Breakdown.

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Presentation on theme: "Chapter 24 Protein Synthesis and Controlled Protein Breakdown."— Presentation transcript:

1 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 1.Amino acids are activated by aminoacyl synthetases using ATP – Amino acids are added to tRNA 2.tRNA molecules with their attached amino acid are brought to ribosome 3.The growing peptide chain is added to each new amino acid 4.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 Prokaryote ribosomes – Subunits 23S and 5S pieces of RNA and 34 proteins 16 S piece of RNA and 21 proteins – Total 50S (large subunit) 30S (small subunit) Ribosomes


11 Translation Initiation Shine-Dalgarno 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 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 – 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

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