Homework2Solutions - BMB 461 Fall Semester 2008 Homework...

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BMB 461 Fall Semester 2008 Homework Assignment #2 Key posted -- Thursday, September 11 In addition to the questions below, you should look at Lehninger, Nelson, and Cox, problems for Chapter 3 (pp. 108-110), nos. 8, 11, 13, and 18. Solutions are in the back of the book. For some of these problems, you will need p K a values found in your notes (preferred) or in textbook on page 73 in Table 3-1. For those problems related to protein purification, you should refer to Tables 3-2 and 3-6 in your text. 1.) Be able to name the 20 standard amino acids without looking them up, draw their side chains, and give their three-letter codes. Solution: See Figure 3-5 in your text 2.) Draw the following oligopeptides in their predominant ionic forms at pH 7: a) Phe-Met-Arg, b) tryptophanyllysylaspartic acid c) Gln-Ile-His-Thr Solution: Key points are a positively charged amino terminus, negatively charged carboxyl terminus, (+) charge on guanido group in (a), (+) charge on Lys and (-) on Asp in (b). For (c) the His is about 90% 0 and 10% (+), should be drawn neutral. a) + H 3 NC H CH 2 C O H N C H C O CH 2 CH 2 NH CH C CH 2 O - O CH 2 CH 2 NH C NH 2 NH 2 + S CH 3
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b) + H 3 NC H C CH 2 O NH H NC H C CH 2 O - O C O - O NH CH C CH 2 O CH 2 CH 2 CH 2 NH 3 + c) + H 3 NC H C CH 2 O CH 2 C NH 2 O H NC H C CH O CH 3 CH 2 CH 3 H NC H C CH 2 O N NH H NC H C CH O - O OH CH 3 3.) How many different pentapeptides are there that contain one residue each of Gly, Asp, Tyr, Cys, and Leu? Solution : The first residue can be one of five amino acids, the 2 nd one of the remaining four, etc. N = 5x4x3x2x1 = 120 4.) Draw the structure of the oligopeptides Val-Cys and Ser-Cys-Pro with their cysteine residues cross-linked by a disulfide bond. + H 3 NC H C CH O CH 3 CH 3 H NC H C CH 2 O - O S + H 3 NC H C CH 2 O OH H NC H C CH 2 O S N C O - O
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5.) What is the isoelectric point of alanine? glutamic acid? lysine? Solution: The isoelectric point of an amino acid is the average of the two pK a values corresponding to the ionization of the form with zero net charge. For amino acids with neutral and unionizable side chains such as alanine , the zwitterionic form has no net charge, and the pI is simply the average of pK
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This note was uploaded on 09/15/2008 for the course BMB 461 taught by Professor Stoltzfus during the Spring '07 term at Michigan State University.

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Homework2Solutions - BMB 461 Fall Semester 2008 Homework...

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