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UCLA CHEM 153A - Practice Final Exam KEY

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Chemistry 153A Practice Final Exam KEY Question # Value Score 1 25 2 5 3 10 4 10 5 7 6 14 7 18 8 15 9 18 10 20 11 20 12 16 13 25 14 17 15 15 TOTAL TOTAL COURSE SCORE FINAL COURSE GRADE First letter of your last name _____ ___________KEY______________ Print your full name (Last Name First) ______________________________ Print your TA's name ______________________________ Time and day of your discussion section I have read the instructions below. ______________________________ Signature INSTRUCTIONS READ EACH QUESTION CAREFULLY! SHOW YOUR CALCULATIONS! WRITE YOUR LAST NAME IN THE SPACE PROVIDED ON EVERY PAGE OF THE EXAM. NO CREDIT WILL BE GIVEN FOR ANYTHING WRITTEN ON THE BACK OF A PAGE OR IN A SPACE OTHER THAN THAT PROVIDED FOR YOUR ANSWER. ANSWERS MUST BE BRIEF AND TO THE POINT. WHERE WORD LIMITS ARE GIVEN, NO CREDIT WILL BE GIVEN FOR THE PART OF YOUR ANSWER THAT SIGNIFICANTLY EXCEEDS THAT LIMIT. Numbers in parentheses represent the point values. Gas constant: R= 8.31 x 10-3 kJ/ oK/mole F ay’s cons .5 arad tant: 96 kJ V-1 mol-1Page 2 1. (25) a. The complexity of living cells is indicated by the _Number _ and average _Size or (Molecular weight)_ of different molecules of which they are composed. b. The statement that water is amphoteric means that a water molecule can be a _Proton__ donor or acceptor and can thus form a _hydroxide_ ion or a _hydronium_ ion. c. The extraordinary cohesiveness of water is attributed to extensive _hydrogen_ _bonding_ between molecules. d. pH is a property of a _solution__ while pKa is a property of a _weak acid__. e. If a weak acid is dissolved in a solution at a pH that is greater than its pKa by one pH unit or less, the addition of H+ to the solution will result in increased _protonation_ of the weak acid. This will tend to minimize the change in the _pH___ of the solution. f. The inductive effect of the α-carboxyl group of an α-amino acid will tend to lower_ the pKa of the α-amino group, and the electrostatic effect of that same α-carboxyl group will tend to _raise the pKa of the α-amino group. g. The peptide plate concept arises from the restriction of rotation around bonds due to steric hindrance. TRUE FALSE h. Would you expect polar amino acids at the outer surfaces of proteins to be more likely to hydrogen bond to water molecules or to each other. _water________ Why? They will be in close contact with many more water molecules than with other polar amino acid side chains. i. Would you expect an α-helix of polyalanine to be disrupted by placing the polypeptide in an organic solvent? _No____ Explain your answer. [≤ 40 words] The hydrogen bond stabilizing the α-helix will be strong in the apolar organic solvent, and contact of alanine side chains with an organic solvent at the surface of the helix would not be unfavorable. 2. (5) Which of the following forms of alanine would you be unlikely to detect in aqueous solution at any pH? [correct answer is indicate by a check mark] √ +H3N C COOHHCH3AlanineH2N C COOHHCH3Alanine+H3N C COO–HCH3AlanineH2N C COO–HCH3AlanineName: ____________________________________ page 3 3. (10) Below is a depiction of the relative radial positions of amino acid residues of an alpha helix, looking down the axis of the helix. 123456891011121314151671718 Circle the polypeptide below that would be most likely to form an amphipathic α-helix? [check marked below] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 √ ser-val-ala-asn-ala-leu-met-lys-val-ala-thr-asp-phe-asp-gln-glu-leu-his-ala ser-trp-tyr-phe-ala-thr-met-leu-his-ala- phe-arg-trp -ile-gly-glu-leu-his-ala arg-leu-ser-ala-lys-val-glu-ile-asp-phe-his-asp-cys-gln-met-tyr-ala-asn-ala 4.(10) a.(2) How do you calculate the number of possible stereoisomers of a monosaccharide? # of stereoisomers = 2n, where n = # of chiral centers (asymmetric carbons) b. (2) Which has more stereoisomers, an aldopentose or a ketohexose? they have the same #_ c. (6) While doing ecological research in the Masi Mara plains of Africa, a friend of yours discovers a new sub-species of Thompson Gazelle that seems to have a selective survival advantage, enabling its population to grow rapidly relative to the general population of Thompson Gazelles. On closer observation your friend observes that the new sub-species is capable of faster bursts of speed, making it more successful at fleeing from lions, leopards, and cheetahs. As a renowned biochemist and geneticist, you join her to investigate the nature of the mutations leading to this enhanced ability. You find that there appear to be some mutations affecting the carbohydrate storage enzymes of this sub-species leading to a change in the structure of a particular polysaccharide. What is the identity of this polysaccharide and the nature of the structural change? [≤ 30 words] A mutation in a gene coding for a glycogen storage enzyme has resulted in synthesis of glycogen molecules that are more highly branched. The resulting increase in non-reducing ends allows faster mobilization of glucose providing a potential for more rapid release of energy for running.Name: ____________________________________ page 4 5. (7) a. Which of the following lipids is not a component of biological membranes? _____C____ A. glycerophospholipids B. sphingophospholipids C. triacylglycerols D. cholesterol b. Triacylglycerols provide highly reduced energy storage. TRUE FALSE c. Integral membrane proteins always have a higher percentage of hydrophobic residues than soluble aqueous proteins do. TRUE FALSE d. A membrane rich in stearic acid would be less fluid than one rich in oleic acid. TRUE FALSE e. Glycerol is the parent compound for the major lipids of the myelin sheath. TRUE FALSE f. Biological membranes are rich in phosphate. TRUE FALSE g. The bonds between fatty acids and glycerol in glycerolipids are ____ester______ linkages. 6. (14) Evidence indicates that some of the following events occur as hemoglobin carries out its natural function. Indicate the proposed normal sequence of these events reflecting their cause and effect relationships by assigning each event a number indicating the order of occurrence. If two events seem to occur simultaneously give the lower number to the event that causes the other. Use an X to indicate any


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UCLA CHEM 153A - Practice Final Exam KEY

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