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lec15 - MIT OpenCourseWare http/ocw.mit.edu 7.88J Protein...

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MIT OpenCourseWare http://ocw.mit.edu 7.88J Protein Folding Problem Fall 2007 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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7.88 Lecture Notes - 15 7.24/7.88J/5.48J The Protein Folding Problem Ribosomes and In Vivo Folding A. Ribosomes Ribosomes: Source of all Proteins! In prokaryotes, all ribosomes within cytoplasm; However, multiple delivery compartments: PP chains >> cytoplasm PP Chains >> inner membrane PP chains >> organelles e.g. flagellum PP chains >> through membrane to periplasm PP chains >> through membrane and periplasm to outer membrane PP chains >> secreted outside cell. Export pathways use protein channels - poorly defined, very active area of research; Polypeptide chains have a leader sequence whose recognition brings them to channel; this is recognized by a leader peptidase, which cleaves off leader sequence, coupled to transit. In Eukaryotes: Cytoplasm Exported through Endoplasmic reticuluum (Signal Recognition Particle) > Golgi> export Imported into Mitochondria or chloroplasts Translocated to Nucleus Inserted into Membranes: Many others, e.g. lysosomes Rate of Prokaryotic Cytoplasmic Protein Synthesis: Forschammer and Lindahl (1971) J. Mol. Biol. 55, 563-568. About 20,000 ribosomes/cell in rapidly growing E. coli Rate of synthesis = 21aa/second/ribosome in coli growing in broth at 37 o C.
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