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490 Chapter 26 AMINO ACIDS, PEPTIDES, PROTEINS, AND NUCLEIC ACIDS: POLYMERS IN NATURE COOH + + + + (g) H NH₂ (1) H NH₂ (7) (CH₂)₃NHCNH₂ (CH₂)₃NHCNH₂ + H NH₂ (12) H₂N H NH (14) (CH₂)₃NHCNH₂ (CH₂)₃NHCNH₂ COOH coo- + + (h) H (1) H (7) H (9.5) H (12) CH₂ CH₂ CH₂ CH₂ OH OH OH 33. (a) Arg, Lys; (b) Ala, Ser, Tyr, His, Cys; (c) Asp 34. First identify the net charge-neutral structure, which is always the one with a single + and a single - charge. Choose the two values that bracket that structure. They are, repectively, the for deprotona- tion of the most acidic group in that structure and the pKₐ for protonation of the most basic group. Their average is the pl. (c) (9.0 + 10.5)/2 = 9.7 (d) (9.2 + 6.1)/2 = 7.6 (e) (8.2 + 2.0)/2 = 5.1 (f) (3.7 + 1.9)/2 = 2.8 (g) (12.5 + 9.0)/2 = 10.8 (h) (9.1 + 2.2)/2 = 5.7 35. The solutions for all three follow the same pattern. First, find the structure of the amino acid target. based upon the reactions you have been told to use (which result in attaching an amino group to the α-carbon), begin each with a carboxylic acid lacking the amino group: cat. (a) For Gly, CH₃CO₂H BrCH₂CO₂H + (b) For cat. (c) For Ala. CH₃CH₂CO₂H cat. PBr₃ CH₃CHBrCO₂H