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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Carbon Source Rate Succinate 16/sec Glucose 21/sec Acetate 12/sec Casamino acids 20/sec Ribosomes proceed 5’ to 3’ down mRNA. In eukaryotes, generally 3-5 fold slower – {3-6 amino acids/second (soft number}: Morphology and Composition of 70s Prokaryotic Ribosomes: E. coli bacteria: Small 30s and large 50s subunits; 2.6 x 10 6 Daltons total; RNA: Protein 2:1 by weight; RNA as Mg++ salt; Only 1gmH 2 0/gm ribosomes - compact, dense; 1 each of 53 protein chains 30S subunit: RNA Protein Mol. wt. 16s RNA - 1542 bases: 21 diff. Chains 1.0 x10 6 120A x 230 A 50S subunit: 23s RNA - 2904 bases 34 diff. Chains 1. 7 x 10 6 60A x 220 x 220A 5s RNA -120 bases.
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This note was uploaded on 11/11/2011 for the course BIO 7.344 taught by Professor Bobsauer during the Spring '08 term at MIT.

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

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