final 2004

Final 2004 - Seat Chemistry 153A Winter 2000 Final Exam KEY Question Value 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 18 14 29 10 13 12 8 21 18 40 10

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Seat # ______ Chemistry 153A Winter 2000 Final Exam KEY Question # Value Score 1 30 2 27 3 18 4 14 5 29 6 10 7 13 8 12 9 8 10 21 11 18 12 40 13 10 14 15 15 12 16 23 TOTAL 300 TOTAL COURSE SCORE FINAL COURSE GRADE
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Seat # ______ 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 ANY PART OF YOUR ANSWER THAT SIGNIFICANTLY EXCEEDS THAT LIMIT. Numbers in parentheses represent the point values. G o ’ of ATP hydrolysis = -30.5 kJ/mole Gas constant: R= 8.31 x 10 -3 kJ/ K/mole 2.3RT = 5.7 kJ/mole for std. cond. or 5.9 kJ/mole for biol. cond. Faraday’s constant: 96.5 kJ V -1 mol -1
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Name______ KEY _____________________ 1 1. (30) a. (5) You make a solution by adding 0.220 moles of A - , the conjugate base of a weak acid, HA (pKa=6) to pure water. You adjust the final pH of the solution to precisely pH 5 and bring the total volume to 1 liter by addition of more water. What is the molar concentration of each of the following species in this solution? H + ___ 10 -5 ______ M OH _ ____ 10 -9 _____ M A - ___ 0.020 ____ M HA ___ 0.200 _____ M H 2 O___ 55.5 _____ M b. (2) Which do you expect to have a greater effect on the pH of the above solution, the addition of 20 millimoles of HCl or the addition of 20 millimoles of NaOH. ____ HCl ___________ c. (2) Based on your answer to b above, write an equation representing the reaction responsible for the change in pH. HCl + H 2 O H 3 O + + Cl - d. (10) Complete the following drawing of L--methionyl-L-histidinyl--L-asparagine in the form that would predominate at pH 9. Show the stereochemistry of the α -carbons by using appropriate wedge shaped and dashed bonds to each side chain and to each α− hydrogen. There is no need to show any stereochemistry within the side chains. H 2 N C C N C C N C COO CH 2 H CH 2 H CH 2 H H H O O C CH 2 S CH 3 N NH O NH 2 e. (8) Draw a titration curve (pH vs. H + equiv.) for the peptide in d above using standard pka’s given in the compendium. H + equivalents 0 .5 1.0 1.5 2.0 2.5 3.0 2 4 6 8 10 12 14 pH 3.5 4.0 f. (3) Calculate the isoelectric point for this tripeptide. pI = (6+8)/2 = 7
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Name______ KEY _____________________ 2 2. (27) a. (5) Consider glycine and β -alanine whose structures are shown below. COO CH H 3 N H COO C C H H H H 3 N H 1) Is either of these compounds optically active (i.e. do they have stereoisomers)? _ No ___ If so, which? __ NA _____ 2) Which of these compounds do you expect to have the higher pka for deprotonation of its carboxyl group? β -alanine 3) Which is a protein amino acid? __ glycine ___ b. The instructor of your analytical chemistry laboratory course gives you a test tube and tells you it contains a pure solution of alanine that has been purified from a base hydrolysate of an alanine rich protein. You determine that the compound in the solution indeed has two ionizable groups having pKa’s consistent with the α -amino and α -carboxyl groups of alanine.
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This note was uploaded on 08/04/2008 for the course CHEM 153A taught by Professor Staff during the Fall '05 term at UCLA.

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Final 2004 - Seat Chemistry 153A Winter 2000 Final Exam KEY Question Value 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 18 14 29 10 13 12 8 21 18 40 10

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