Post-Translational Events I Translocation of Newly Synthesized Proteins into Membranous Organelles.
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Transcript of Post-Translational Events I Translocation of Newly Synthesized Proteins into Membranous Organelles.
![Page 1: Post-Translational Events I Translocation of Newly Synthesized Proteins into Membranous Organelles.](https://reader035.fdocuments.net/reader035/viewer/2022062804/56649cf75503460f949c7c69/html5/thumbnails/1.jpg)
Post-Translational Events I
Translocation of Newly Synthesized Proteins into Membranous Organelles
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Locations of Protein Synthesis
• ER Associated Ribosomes– proteins translocate co-translationally into ER
lumen– subsequent processing & transport through
Golgi for secretory vesicles and lysosomes
• Cytoplasmic Ribosomes– proteins translocated post-translationally into
membranous organelles (except Golgi, ER and lysosome)
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Transport of Cytoplasmically Synthesized Proteins
• Import into organelles (transmembrane and lumenal)– Mitochondrial import– Chloroplast import– Peroxisome import
• Translocation across plasma membrane
• Insertion in cytoplasmic face of plasma membrane
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Signal Sequences
• Portions of protein sequence– Frequently N-terminal, C-terminal– Occasionally located within– Often cleaved following transport event
• Signal Recognition Particles/Complexes– protein-translocation channels– escort (chaperone) proteins
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Mitochondrial Protein Import
• Four Destinations– Outer membrane– Innermembranous space– Inner membrane– Matrix
• TOMs– Translocase of the outer
mitochondrial membrane
• TIMs– Translocase of the inner
mitochondrial membrane
• Tiny TIMs– escorts of the innermembranous
space
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TOM & TIM Function
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Tiny TIMs and TIM22
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TOC & TIC
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Peroxisome Import
Signal sequence for recognition by PEX5
-SKL-COOH
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Peroxisome Formation
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Translocation of ER-Associated Ribosome Synthesized Proteins
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Docking of Ribosomes to ER
Signal peptides typically 10-20 residues – shorter than those on cytostolically synthesized proteins
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Signal Recognition Particle• Ribonucleoprotein complex• Similar to bacterial SRP
Ribosome binding Signal peptide binding
translocation
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Translocation of Various Classes of ER Proteins
lumenal proteins
Type 1 transmembrane proteins
Type 2 transmembrane proteins
multipass transmembrane proteins