nov 1 protein sorting modification turnover

nov 1 protein sorting modification turnover - T r a n s la...

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1 Control of gene expression includes control of: • post-translation modification • localization • degradation (linking genetic and cell biology processes) Translation at the ribosome : the first step in the life of a protein. Purves Fig. 12.13 Degradation in a proteosome : the death of a protein. Purves Fig. 14.22 Some protein molecules persist for years; others are degraded only minutes after they are synthesized. Protein sorting The polypeptides generated by translation are targeted to specific sites within or outside of the cell. Cytoskeletal proteins are synthesized in the cytosol, and do not leave it. ! urve " 12.14 Purves 12.14 Nuclear proteins : histones; DNA and RNA polymerases; transcription factors. Nuclear proteins ( histones; DNA polymerase, RNA polymerase; transcription factors) contain a specific sequence of amino acids called a nuclear localization signal sequence . If a single amino acid residue is changed by mutation, the protein cannot be imported into the nucleus and will remain in the cytosol. Purves 12.14 Some proteins are targeted to enter cytoplasmic organelles through the addition of “address labels” after translation. Purves 12.14 Many proteins are either targeted to the plasma membrane or secreted into the extracellular space. These extracellular proteins must pass through the endomembrane system. mRNA NUCLEUS Transcription Following transcription, all mature mRNAs exit the nucleus through nuclear pores , and thus come to lie in the cytosol. Some of these mRNAs encode proteins that will enter the
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nov 1 protein sorting modification turnover - T r a n s la...

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