5.Why is the following not a good two step route for the preparation of pure L-alanine? catalytic excess CH:CH2CO2H Br2 PBr2 NH The bromin a secondary brom Only the CHa group is brominated The product will he racemie E)Propanamide would be the major product. Ans:D 6.Disulfide bonds in proteins B刷 (RSH) h f proteins mk e in e can be broken n E) All of these are true. Ans:E 7.Which amino acid does not form ac B) Lysine E)Tryptophan 8.What material can be used repetitively (on a given sample)to sequence a polypeptide from the N-terminal end? A)Chymotrypsin D)Edman reagent B)Sanger reagent E)Carboxypeptidase Ans:Drypsin 9.How many tripeptides containing one residue each ofLalanine,L-valine,and glycine ssibl B)3C)4D)6E)9 Ans:D Page2 Page 2 5. Why is the following not a good two step route for the preparation of pure L-alanine? CH3CH2CO2H + Br2 catalytic PBr3 excess NH3 A) The bromination is not selective (the CH3 and CH2 groups are both brominated). B) Ammonia is not sufficiently nucleophillic to react with a secondary bromide. C) Only the CH3 group is brominated. D) The product will be racemic. E) Propanamide would be the major product. Ans: D 6. Disulfide bonds in proteins A) result from oxidation of thiols (RSH). B) function to help maintain the shape of proteins. C) can be broken by reduction reactions. D) link two cysteine amino acid residues. E) All of these are true. Ans: E 7. Which amino acid does not form a characteristic blue color with ninhydrin? A) Cysteine B) Lysine C) Proline D) Valine E) Tryptophan Ans: C 8. What material can be used repetitively (on a given sample) to sequence a polypeptide from the N-terminal end? A) Chymotrypsin D) Edman reagent B) Sanger reagent E) Carboxypeptidase C) Trypsin Ans: D 9. How many tripeptides containing one residue each of L-alanine, L-valine, and glycine are possible? A) 2 B) 3 C) 4 D) 6 E) 9 Ans: D