CChheemm 44334433Exam # 2 Oct. 27th, 2004 Name : Answer any seven of questions 1-8 . Each question is worth 15 points for a total of 105 points.1. (i) For the dipeptide Asp-Glu draw its structure at pH values of 1, 4 and 11(ii) Determine, showing your method, the isoelectric point for the peptide in (i) above(iii) Determinewhich of the following polypeptides, each composed of only one amino acid, ismore soluble in water at pH=7 and explain your reasoning :(-Met-)20or (-Glu-)202. (i) A solution of benzyl mercaptan, C6H5-CH2-SH is spilled and you have to clean it up. If youare told that you can use water, soap, acid or base to clean it up decide, giving your reasoningwhich combination you would choose. Note : pKa (C6H5-CH2-SH) = 8.0(ii) The amino acids GLY and ASP both tend to be found in turns, such as that shown below.Identify .the structural features of both that might account for this tendency(iii) The majority of proteins inside an organisms cell do not contain disulfide bridges. What does this tell us about the conditions typically prevailing inside a cell.3. (i) A normal patient has the following amino acid sequence in their hemoglobin:-Val-His-Leu-Thr-Pro-Glu-Glu-Lys – 1 2 3 4 5 6 7 8The hemoglobin from a patient with sickle-cell anemia has an isoelectric point (pI) +0.23 higherthan that of the normal patient. Propose a different 1o structure for the sickle-cell patient byidentifying a sequence with one different amino acid from the sequence above. Give yourreasoning.(ii) A GLU is substituted for a LYS in the central cavity of the Hemoglobin tetramer (page 224of your text). This causes a condition called “Providence” anemia. Explain the effect of thissubstitution on the function of Hb(iii) Skindivers often hyperventilate, breathe rapidly and deeply, before making a protracteddive. Explain any beneficial effects of this activity.4. (i) Predict, giving your reasoning, whether sucrose (table sugar) or glucose is more soluble inwater.(ii) Paper, obtained by the treatment of and extraction from wood pulp, loses most of its strengthwhen wet with water, but retains its strength when wet with oil. Explain.(iii) Stearic acid has a melting point of 69.6 oC while oleic acid has a melting point of 14 oC.Explain this observation and describe how you might tell these two fatty acids apart.stearic acidOOHoleic acidOOH5. (i) Identify the two structural features or motifs labeled A and B in the accompanying diagram.(ii) Lysozyme is a small enzyme which hydrolyzes polysaccharide chains using amino acidsGlu35 and Asp52 as shown below. Identify a pH, giving your reasoning, for this reaction:(i) Cellulose, shown below, is a fairly rigid molecule, with little ability to rotate around the C1-Oand the C4-O bonds. Explain this lack of rotation in terms of forcesC1OO*C4OOHHOOOOCH2OHOHOHHFor Questions 6-8 indicate all answers (i) through (v) that are correct6. Which of the following statements are true of peptides and proteins:(i) phenylalanine is most likely to be found on the surface of a protein(ii) proteins with high proline content will tend to have substantial helix composition(iii) methionine is more likely to be part of a helix rather than part of a β-sheet(iv) renaturation involves refolding of the protein and oxidation of the disulfide linkage.(v) adjacent cysteine amino acids are necessary for the formation of disulfide bridgesComment7. Which of the following statements are of the immune response :(i) antibodies elicit a response by stimulating the production of antigens(ii) the antibody structure includes variable and constant regions connected by disulfide bridges(iii) the antibody alters the antigen shape to produce antigens specific to the antibody(iv) the antigen alters the antibody shape to produce antibodies specific to the antigen(v) an antibody can respond to multiple antigensComment8. Which of the following statements concerning protein structure are correct :(i) hydrogen bonds for α-helices and β-sheets occur primarily between CO and NH groupson the main chain(ii) hydrogen bonds for α-helices are primarily inter-chain(iii) hydrogen bonds for β-sheets are primarily intra-chain(iv) the folding of α-helices and β-sheets to give the 3o structure yields a -ve ∆Soffset by a +ve ∆S due to the hydrophobic effect(v) the folding of α-helices and β-sheets to give the 3o structure yields a +ve ∆Soffset by a -ve ∆S due to the hydrophobic