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Unformatted text preview: BC367, Fall 2011 Problem set #6 Due: Friday, November 4th (Hand‐in problems must be done on separate pages & short answer questions typed) 1. The sweetness of honey can be attributed to β‐D‐fructopyranose, one of the sweetest‐tasting carbohydrates known. However, cooking with honey can be problematic because honey can lose its sweetness after being heated. Sucrose (table sugar) retains relatively constant sweetness upon heating. Speculate as to why this happens. 2. Biochemists often synthesize custom biopolymers for research. Proteins and nucleic acids, for instance, can be synthesized using solid phase synthesis. Why are custom, synthetic polysaccharides so much less available as research tools? 3. The values of the specific rotation for the α and β anomers of D‐galactose are 150.7° and 52.8°, respectively. A mixture that is 20% α‐D‐galactose and 80% β‐
D‐galactose is dissolved in water at 20°C. What is the initial specific rotation of the mixture? After several hours, the specific rotation of the mixture, now at equilibrium, is 80.2°. What is the mixture’s anomeric composition? 4. Galactomannans are polysaccharides consisting of mannose backbones and galactose side‐groups. The mannopyranose units are linked with 1β→4 linkages to which galactopyranose units are attached with 1α→6 linkages. Galactomannans are present in several vegetable gums that are used to increase the viscosity of food products. Guar gum (shown below) is perhaps the most well‐known galactomannan. a. What is the relationship between the two monosaccharides of guar gum? b. What is the orientation of the bond connecting the galactose to its mannose residue in guar gum? c. Guar gum is most similar to which of the following: i. starch, but more compact, ii. starch, but less compact, iii. cellulose, but a stronger fiber, or iv. cellulose, but a weaker fiber? Explain. ...
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