3 - MCB102 Summer 2009 Problem Set 3(all are former exam...

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MCB102 Summer 2009 - Problem Set 3 (all are former exam questions) Questions from the (scheduled) post-exam lecture: 1. Check TRUE or FALSE for each statement. If you mark a statement false, provide a thorough explanation of what is wrong about it. a. The D and L forms of galactopyranose are readily interconvertible in solution. _______ TRUE _______ FALSE The reason this statement is false is: b. Under alkaline conditions, lactose is capable of reducing Cu ++ to Cu + , but sucrose is not. _______ TRUE _______ FALSE The reason this statement is false is: 2. The same carbohydrate figure is (well, was on the exam :-) printed three times for your convenience. a. For part ‘a’, please circle (very precisely) the anomeric carbon or carbons in this molecule. b. Carefully circle the carbon or carbons that are in the alpha configuration (or if you find none in this configuration, circle the word ‘none’). c. Carefully circle the carbon or carbons that are capable of becoming oxidized by Cu ++ , reducing it to Cu + in the process (or if you find no carbons that will do this, circle the word ‘none’). d. Please choose the name for this molecule. Rather than write out 64 possible names for this compound and having you search for the right one, I have given you lists to choose from for each component of the name. Please circle the one correct entry from each column. α D-glucopyranosyl (1-->1) α D-glucopyranose β D-glucofuranosyl (1–>2) β D-glucofuranose (1–>4) (1–>6) 6. (2008) Knowing that α - D -mannose is very sweet, but β - D -mannose is bitter, Mr. Teadrinker carefully selects a powder of purified α - D -mannose to sweeten his iced tea. He makes a pot of tea with boiling water, adds the α - D -mannose, and then puts the tea away to cool, and goes off to work. When Mr. Teadrinker comes home from work and takes a sip of his iced tea, he discovers that the tea tastes terrible - very bitter, in fact. He calls up the company that sold him the α - D -mannose, to complain that they must have made a mistake in labeling their sugars, and sold him the bitter β - D -mannose instead. You are the customer service representative who takes Mr. Teadrinker’s call. Since you have studied sugars in biochemistry, please explain to him, with all the proper technical terms , precisely why this correctly labeled, pure α - D -mannose powder has produced a bitter-tasting tea.
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4. a. In the figure, what type of bond links the two carbohydrate monomers to each other? Answer by checking in the space(s) provided at right. Check all that apply; or check ‘none of the above’ if none of the descriptions applies to the bond shown. _____ glycosidic bond _____ ester bond _____ hemiacetal bond _____ acetal bond _____ hemiketal bond _____ ketal bond _____ a furanose bond _____ a pyranose bond _____ none of the above [for part d: ] NONE b. Describe the linkage between the two monomers by circling the one correct choice in each column : α 1 1 β 2 2 3 3 4 4 5 5 6 6 c. Will the molecule shown be able reduce Cu ++ to Cu + , under alkaline conditions?
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