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Midterm_WI13_Key

These proteins also assist the folding of non native

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These proteins also assist the folding of non-native polypeptides into their stable conformation.(2pt) 9. Describe the classical Anfinsen experiment with ribonuclease in detail.
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a. What is the result of this experiment (5pts)? Ribonuclease A was treated with 2-Mercaptoethanol + Urea to break (reduce) the disulfide bridges, under those conditions the protein unfolded (1.5pt) 2-ME was removed and the protein folded into an inactive conformation with incorrectly positioned disulfide bridges (1.5pt) Urea was removed and only traces of 2-ME were left, the protein folded into its functional native conformation. This demonstrated that refolding could take place in vitro once the cause of denaturation was removed(2pts) b. What does it mean (5pts)? Sequence determines structure (5pts) c. What is the overall significance for structural biochemistry (5pts)? Anfinsen used Ribonuclease A for his experiment, but the results can be applied to any protein in nature(5pts) Explain what the hydrophobic effect is, why it occurs, and its significance for protein folding (5pts). In an unfolded protein, all of the hydrophobic portions of the polypeptide are exposed to the aqueous environment, and the water molecules order themselves around the hydrophobic residues in ordered structures called hydration spheres.(1pts) As a protein is folded, these hydrophobic residues initially exposed to the aqueous environment are buried in the interior of the protein hidden away from contact with water. The Hydrophobic effect is the driving force toward the folding state(2pts) The entropy of the water molecules increases as the need for hydration spheres diminishes, in effect overcoming the entropy decrease for the protein alone. (1pt) while the entropy of the system (the protein) decreases, the entropy of the surroundings increases to a greater degree, leading to an overall increase in entropy for the universe.(1pt)
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These proteins also assist the folding of non native...

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