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CHEM153A_midterm1_L2_S09_answers - So the possible...

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Chemistry 153A, Spring 2009, Lecture 2 Midterm 1, Exam A – Answer Key 2. a. True b. True c. False d. False e. True f. True g. True h. False; β-sheets don’t have a dipole moment. i. True j. False; because of their structural differences, proteins and polysaccharides adopt different dihedral angles. 3. a. D b. B c. A d. A e. C 4. d 5. a. A, B, C, E b. E c. C d. D e. B f. B g. E 6. The switching of anomeric configurations in a cyclic sugar. 7. a. Asn b. Tyr, Phe, Trp c. Based on the titration curves, one dipeptide contains a Lys residue (pKa 10.5), and the other contains an Arg residue (pKa 12.5). We don’t know which dipeptide came from the N- versus C-terminus of the tetrapeptide. We know that position 4 is Asn, and position 2 is either Phe or Trp (it cannot be Tyr since there was no titration of the Tyr sidechain).
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Unformatted text preview: So the possible sequences are: Arg-Phe-Lys-Asn (R-F-K-N) Arg-Trp-Lys-Asn (R-W-K-N) Lys-Phe-Arg-Asn (K-F-R-N) Lys-Trp-Arg-Asn (K-W-R-N) 8. a. sugar alcohols b. It depends on which carbon is selected as carbon 1, since both ends of the molecule have equal priority. If the left-hand carbon is C1, the molecule is D; if the right-hand carbon is C1, the molecule is L. c. D-glucose; sorbitol is reduced at carbon 1 (from aldehyde to alcohol) d. glycerol 9. b 10. a. fatty acid b. myristic acid c. 14:0 (or C-14:0) d. B, C, D, F, G, H e. True f. False g. Yes, pyruvate’s carboxyl group should have a lower pKa than that of myristic acid, because of the electron-withdrawing inductive effect of the carbonyl oxygen attached to pyruvate’s carbon 2....
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