2006 - Midterm 2 CHEM 4711, Fall 2006 Oct. 19, 2006...

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Midterm 2 CHEM 4711, Fall 2006 Oct. 19, 2006 Question 1. (10 points) Which of the amino acid sequences given below is most likely to be the α -helix in the structure illustrated. Which is most likely to the β -sheet (either of the β -strands)? You must JUSTIFY your answer to get full credit. (a) LSFAAAMMLAG (b) INEGFDLRSG (c) GVHLDIEVDA (d) KEKDKGKSEE Question 2. (10 points) Organic chemists like to synthesize modified forms of natural molecules and then see how they behave compared to the natural form. Suppose that the 20 amino acids were synthesized as α -methyl amino acids (see below) and from these new amino acids a polypeptide chain was made (such that it contained no normal amino acids). What would you expect the Ramachandran plot for this new protein to look like compared to a normal protein? EXPLAIN. Question 3. (10 points) Suppose you now synthesize a set of amino acids that contain a methylene group in the backbone instead of a carbonyl, such that now there are amine linkages in the backbone instead of amide linkages. You create a polypeptide from these amino acids (see illustration below) and note that it folds into a three-dimensional structure much like a normal protein (side chains are the same as those of the natural examples:
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amino acids). How would the entropy of folding (
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2006 - Midterm 2 CHEM 4711, Fall 2006 Oct. 19, 2006...

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