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CHEM153A_midterm1_L1_S09_answers - Chemistry 153A Spring...

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Chemistry 153A, Spring 2009, Lecture 1 Midterm 1, Exam A – Answer Key 2. True or False? a. False. Water is only polar. b. False. The stronger an acid, the lower its pKa. c. True d. False. Bonds to α-carbons each sit in a peptide plane, and there is rotation about these bonds. e. True f. True g. False. Backbone carbonyl groups point toward an α-helix’s carboxyl -terminal end. h. True i. False. The 3.3 helix of collage is left- handed. j. False. Peptidoglycan provides stability to the bacterial cell wall. 3. e; explanation: a. is false, because a reducing sugar becomes oxidized in the presence of Cu 2+ . b. is false, because some reducing sugars (ex: glyceraldehyde) cannot form a ring. c. is false; a polysaccharide can have reducing and non-reducing ends, but the molecule as a whole will be either reducing (if it has a reducing end) or non-reducing (if all ends are non-reducing). d. is false; the monosaccharide on the right has its anomeric carbon in the hemi-acetal form, so it is reducing.
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