15.Translation1

15.Translation1 - Protein Synthesis: General Features...

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Protein Synthesis: General Features Polypeptide Synthesis: N- to C-terminus Ribosomes read mRNA in 5’ to 3’ direction Many ribosomes read single mRNA Polyribosomes, polysomes Peptide on tRNA in P site is added to N- terminal end of amino acid on tRNA in A site P site: polypeptide site A site: acceptor site
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Figure 32-40 Electron micrographs of polysomes from silk gland cells of the silkworm Bombyx mori . Page 1319 Polyribosomes • Beads on a string • 50 to 150 Å apart ~1 ribosome per 80 nt of mRNA
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Figure 32-41 Ribosomal peptidyl transferase reaction forming a peptide bond. Page 1320 N-term C-term Polypeptide Synthesis Schematic Amine nitrogen attacks carboxlester linkage to form peptide bond
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What happens after peptide bond formed? Uncharged tRNA in P site moves to E site tRNA with polypeptide chain in A site moves to P site New tRNA with next AA brought to A site EVERYTHING MOVES TO THE LEFT
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Translation Initation: Prokaryotes Formylated Met is N-terminal residue Amide group protected • tRNA f Met is distinct from tRNA m Met Recognize same codon • Met is added to tRNA f Met , then formylated Formyl group, and sometimes Met, removed during post-translational processing HC -NH-CH-C-O-tRNA f Met O O R
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Figure 32-42 Nucleotide sequence of E. coli tRNA f Met shown in cloverleaf form. Page 1321 Initiator fMet tRNA is Distinct
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How is Initiator AUG Distinguished from Internal AUG? TRANSLATION INITIATION IN PROKARYOTES 1. Masking of internal AUGs by mRNA secondary structure. 1. Interactions between mRNA and 16S rRNA of small ribosomal subunit. Y-rich sequence at 3’-end of 16S rRNA complementary to R-rich 3-10 nt Shine-Delgarno sequence (1974)
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Figure 32-43 Some translational initiation sequences recognized by E. coli ribosomes. Page 1321 Shine-Delgarno Sequence 10 nt upstream of initiator AUG (GUG) codon 3’-end of 16S rRNA from Small Subunit base-pairs to set find proximal AUG
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Figure 32-44 Path of mRNA through the ribosomal 30S subunit as viewed from its interface side. Page 1322 Y-Rich 3’-Region of 16S rRNA interacts with S-D of mRNA
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Prokaryotic Translation Initiation: Complex 3-Step Process Two ribosomal subunits along with fMet-tRNAfMet assemble on properly aligned mRNA Requires three Initiation Factors: IF-1 IF-2 IF-3 Table 32-9 The Soluble Protein Factors of E. coli Protein Synthesis. Page 1322
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QuickTime and a decompressor are needed to see this picture. By Brooke Christian
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Figure 32-45 Translational initiation pathway in E. coli .
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This note was uploaded on 03/03/2010 for the course CHEM 431 taught by Professor Pielak during the Spring '07 term at UNC.

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15.Translation1 - Protein Synthesis: General Features...

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