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Lecture3notes_2010 - BIO 320 CELL BIOLOGY Spring 2009...

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BIO 320 - CELL BIOLOGY – Spring 2009 T.O’Halloran & A. De Lozanne Lec 3 Protein Folding &Degradation. Protein modification by Ubiquitin Reading: Alberts, 5th Ed. Pages 388-399. Optional Reading: 3 Review Articles posted on Blackboard: Goldberg, Elledge & Harper. (2001) The Cellular Chamber of Doom.  Scientific American 284:68-73.  Mukhopadhyay & Riezman. (2007) Proteasome-Independend Functions of Ubiquitin in Endocytosis  and Signaling. Science 325:201-205 Sowa & Harper. (2006) From Loops to Chains: Unraveling the Mysteries of Polyubiquitin Chains  Specificity and Processivity. ACS Chem. Biol. 1:20-24 I. Protein Folding A. The folding of a protein is primarily dictated by its amino acid sequence B. During folding the hydrophobic amino acids tend to be buried in the core of the protein  while polar and charged amino acids are exposed on the surface of the protein. C. Some proteins can refold even after being completely denatured (by heat or urea). D. Most proteins begin to fold while still being synthesized. E. Posttranlational modifications and binding of cofactors can influence the folding of a  protein. F. The “molten globule” is an initial state of folding that forms rapidly after protein  synthesis.  G. Folding into a final structure can occur slowly and may need the help of folding factors  (chaperones). H. Proteins that fail to fold properly will be targeted for degradation. I. If misfolded proteins accumulate in the cell they can aggregate and form insoluble  precipitates that can be harmful to the cell. II. The Role of Molecular Chaperones in the Folding of Proteins. A. Many proteins cannot fold properly by themselves, they need the activity of molecular  chaperones B. Some chaperones are specialized to fold a specific set of proteins. C. The most common chaperones or “Molecular chaperones” are also called 'heat-shock  proteins' (HSP) because they assist in the re-folding of proteins after heat denaturation. D. Molecular Chaperones bind to patches of hydrophobic amino acids exposed on the surface of  a protein.
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