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| 1. Since leucine is similar in structure to valine, one would expect the protein to have similar abnormal properties. Since aspartic acid is similar to glutamic acid, which is the proper amino acid, relatively little effect might be expected, but this could only be confirmed by site-directed mutagenesis. 2. Lysine would be the most soluble and isoleucine the least. 3. Four (one straight chain and three branched). Three (two straight chain and one branched), ignoring cis-trans isomerism. 4. The structure of DHAP is on p. 110. It does not have stereoisomers. 5. The fatty acids would tend to contain greater numbers of double bonds (more unsaturated), which would lower their melting point, thus keeping them liquid at the lower temperature. 6. -C-C*-N-C-C*-N-C-C*-NH2. Carbons with an asterisk are alpha carbons. 7. 3 and 4. A rise in pH, would increase the loss of a proton from a -COOH group and from an -NH3+ group. 8. Polar, uncharged. Polar, charged. Nonpolar. 9. It would be expected to slow the rates of the reaction because the products of the first two reactions would diffuse into the surrounding medium rather than be passed directly into the active sites of the second and third enzymes. 10. Yes. Both consist of a single polypeptide chain. 11. 8,000 (20 3 ). 4 carboxyl terminals, one per chain. 12. At pH 7, the amino group of lysine will be positively charged and the carboxyl group negatively charged. At pH 12, the amino group will be uncharged and the carboxyl group will be negatively charged. 13. Glutamic acid has a pK of 4.3. Therefore, above pH 4.3, the side chain is predominantly negatively charged and below pH 4.3 uncharged. Arginine has a pK of 12.5. Therefore, below pH 12.5, the side chain is predominantly positively charged and above pH 12.5 uncharged. For an ionic bond to form, both side chains must be charged. At pH 4, arginine is charged, but glutamic acid is uncharged; at pH 13, glutamic acid is charged, but arginine is uncharged. However, at pH 7 and 12, both groups will be charged and an ionic bond can form. 14. No. The disulfide bonds would not be broken. 15. There are two possibilities. 1) Even though the normal polypeptide normally folds into PrP C , it is possible that on rare occasions it might fold abnormally to form PrP Sc . If this were to occur, the formation of one or a few of the abnormal molecules could lead to a chain reaction that converted normal PrP molecules to the PrP Sc form. 2) A mutation in a gene could arise in a somatic cell that led to the formation of the abnormal PrP Sc in that cell. If that protein was released into the extracellular environment, it could be picked up by other cells whose PrP C could then be converted to the abnormal form, thus causing the disease. 16. If CJD results from a rare, sporadic misfolding of the PrP protein, than the longer a person lives, the more likely the event will occur, and thus the older they are likely to be when they are struck by the disease. 17. Convergent evolution. These examples indicate that a similar grouping of reactive side chains within the active site of a protein can evolve from ancestral proteins that are not related. 18. Yes. Many different sequences generate the same globin fold that is depicted in Figure 2.34a. |