Key_Mid1_Summer08

Key_Mid1_Summer08 - lof2 BIS 102 Name 143 Summer 2008 Last...

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Unformatted text preview: lof2 BIS 102 Name 143% Summer, 2008 Last First K. Hilt First Midterm Score (100): Equations: pH = pK, + log {[b]/[a]} K, = 2/(y-x) K}, = x2/ (y-x) pH = (pKal + pKa2)/2 (K,)(Kb) = 1 x 10'” 1:=(q1 q2)/sr2 AG=AH—TAS Amino acid pK,’s: oc-carboxyl group (2.1), (it-amino group (9.6) side chains: D (3.9) E (4.2) H (6.0) C (8.3) Y (10.1) Oligopeptide pKa’s: C-terminal carboxyl group (3.6), N-terminal amino group (7.4) K (10.5) R(12.5) 1. There are four weak bonds that we have discussed. ( 2 pts.) Which of these is the predominant bond that stabilizes the double helix of DNA? Answer: kg; 3x0 9mm. efrfiui' ( 2 pts.) Which weak bond is the weakest? Answer: am wad/r ( 2 pts.) Which weak bond has its strength affected by changes in temperature? A\ Answer: la b L a: 5 3a N:\\W,¢g ( 2 pts.) Which weak bond has its strength affected by both direction and pH? M m MAL . Answer: 14 -— bmal e 2. ( 20 pts.) Give the one letter code of each amino acid that satisfies the following criteria. If there is more than one answer, then give them all. Do not guess. Points will be subtracted for incorrect answers. a) The R—group is basic: R H 5 MM b) The R-group consists only of three carbons, and the appropriate hydrogens: V P ‘* l a c) The R—group has a sulfur atom in it: M C. A («0‘ d) The R-group absorbs UV light: w F- ‘1’ w Mflé \e) The R—group has an asymmetric carbon in it (an asymmetric carbon has four different chemical m9 " groups attached to it): ‘1' I + D_ 5 wit) The R-group has one or more electronegative atoms in it: N 92 5 1' DE L’ R H V C H w a?” M Mr D K :5 WELL a-$ Slka H'arc, +5— 2> m 6Q; 49" b)? l} +Wi¢¢ m iwl-W5H17 0-0 Ll, km +w a_a.'$ 3. ( 30 pts.) A student spots the amino acids E, H, C, K, and D in the middle of a piece of wetted paper (see oval drawn below), soaked in a buffer at pH 7.8. Electrophoresis is conducted. The paper is dried and then sprayed lightly with ninhydrin, a compound that reacts with amino groups. Draw in carefully where the spots are, labeling each spot with its one letter code and writing its net charge above it. Also indicate the intensity of each spot (i.e. how dark each spot is). Show chugge calculations for each amino acid on the back of this pager to explain why you have drawn the locations of the spots the way you did. The axis labels along the bottom of the piece of paper indicate how far an amino acid with that net charge would travel in this experiment. The position of the two electrodes is shown. Draw the R-group, at pH 7.8, below each spot. 5‘15? locacl'iuvk 597(- MM +2 Net charge: +1 Explain briefly why some spots were darker than others: \aeW K laws. +901: amino abwmm. MW‘ *l a 4-1 u| QIL r7. 31‘ E 7.— E __» E PH7-8 ‘ b. QH’:«K¢,+ U13," 7.8”=‘?b +1433 ~19: Maya: 1; _ a 0.55 b_ b m5? " 1 10:53 (0.3963(4) + (Amiga-23 = L_0_q?45) + b. 0.03:) = D wIH jive, HM. sm Mfi" Marve— aa. 5 H is M" 3+: Bodega/go foiyd—Z +2 2“ +‘ ‘u0 Rib H I‘J—— H fi— A" L H," (mo +1.5 = mg 1, +2 2.\ N «a 10.5 A ’61“ '2— K “EL—K 6376 MISS \\ f” 7'? \ 5m caflwhfim m glam 3w 1‘ C reicrkm M {4.14 __ (20 CD'O Lq‘b)fi‘r~ L,» .3 ‘ 3L / 9“; «pt g «(a *r “’3, o; ‘ 1/ L +0 flflfb'g". (5“) ’75" 93 4’ I“? '~ W“ \E “0 3: [oi/1's; 0&5: L”. b: __ l 6‘ 1.5K. ' 20f2 BIS 102 Name 4. ( 20 pts.) The buffer used to control the pH at 7.8 in the piece of paper in question #3 was a 50 mM phosphate buffer, pH 7.8. The lab that you are in has a bottle containing 500 ml of 50 mM phosphate bufi‘er at pH 12.4. How many moles of IF would be required to change the pH to 7.8? Show all calculations. Assume that the addition of H+ does not significantly alter the vol'l’ume of the 50 mM buffer. The pK.’s of phosphate are 2.12, 7.21, and 12.32. * 3 7"; —3 .500}. 0.05’0 M '5 0.0 H390“ #_ (0 X4. 2 3 a. 5 ' I 1 u - = rad-l / P“? 7‘? 9 L m (H' 7 (’K‘ *1“? F” 5 '2‘- ?laB C57 l;.q-; |232 +;‘% a 7.i=721+/0z5% ““’"'°’2{“ - '= 1' ‘0 s . 05¢ ; 1%}: 3.2.: .. a ,. ‘4 33-3 _, a S"! '—“‘ rat (0.54309st M) = a _ _ + (a ‘ . a ’ H- — 0' 7'0 Hp 3.1.1:)(0. 15' we) :(o.oa§ M2 1% l 5. ( 10 pts.) Which of the following buffers would best contro the addition of some NaOH, i.e. the pH would not change dramatically? Circle the best answer. a) 50 mM buffer B, pH 8.2 (the pK, of B is 7.9) b) 50 mM buffer B, pH 7.6 c 100 mM buffer B, pH 8.2 100 mM bufler B, pH 7.6 6. ( 12 pts.) Dithiothreitol is used to reduce cystine to cysteine. E ' . he ' structures, write the balanced chemical reaction that occurs when cystine reacts with e. w the structures in the form that would predominate at pH 7. (Draw the full structures of cystine, cysteine, and dithiothreitol. Show the balanced chemical reaction). cau’ (430’ “as”, ... + \ .y l — H can A) .. CI ‘4 H ‘ ".9 \GHZ .3 0H2 + "4%.... 2- fly?» + s \ l 0* ‘3 5.1-1»; or‘ \ 5 ___— S i / s 0*25H s H +1, SHWWVC 1‘3 O‘A“V‘a“°' *2 Sh“duv1 4.; SWK. +7, 5+(M0w'c *\ a7 «"9 GD Frequency 3an 2.53:: wo+ mm} Moi a: 40! mil o. _DD:: # _ M w: m m m m w m m mm mm M 933 ><m. mm“ :6... .39 r92 3h D 335:0: ...
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This note was uploaded on 09/10/2008 for the course BIS 102 taught by Professor Hilt during the Summer '08 term at UC Davis.

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Key_Mid1_Summer08 - lof2 BIS 102 Name 143 Summer 2008 Last...

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