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Chem153c_W07_Midterm1

Chem153c_W07_Midterm1 - Name_B_N_“£&_£§I_QP_L 1...

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Unformatted text preview: Name_B_N§_“£§&_£§I__:_QP_L__- 1 Chemistry & Biochemistry 153C Winter 2007 lst MIDTERM EXAMINATION 2 February 2007 (80 points, 3 pages, 50 minutes) PLEASE READ EACH QUESTION VERY CAREFULLY! 1. (20 total points) (part a) (15 points) Polyhydroxybutyric acid is a storage form of excess carbon in many microorganisms. The enzyme polyhydroxy—butyrate depolymerase produces D—beta— hydroxybutyrate. Describe how a microbe would be able to convert D—beta- hydroxybutyrate to CO2 and th How many ATP equivalents are generated by the complete metabolism of D—beta-hydroxybutyrate? Show your logic for full credit. You may use either names or structures. Indicate any cofactors by name. No e- pushing required! OH 0 fi (I) - l _._..__——.———-—> __ CH3 0 fl cHS— c -cH;c—— o H H NAIS" NADH +1 AcEToACETATE D—B—hydroxybutyrate (+ 3 ATP) H A Ke-roNe sow H SHCG'NYL‘W“ ‘H (— \ 4T?) SUICCINfiTE H +1 +4 0 Cb¥MS+l C: fl l fl CHs—g—scoA 6—4— CH3—c—ng—c—saaA +I Aoenlu 60A AoETo A’OETYLCOA ToA CYCLE 3 NAbH +| 6 NAM} |8 ATP H ‘2 | PADH; ‘H ———> .9. PAD”). ——_> H— A‘T‘P -H I 4T? 'H 9. GTP 2 ATP +| TO‘M'L ATP: 3-l+18+++2= 36 ATP (part b) (5 points) Microorganisms metabolizing D—beta—hydroxybutyrate produce acetone as a byproduct (the acetone is not further metabolized). Use appropriate types of arrows to indicate movement of e- and show how this might occur. How would this affect the calculation of net ATPs in part (a)? +1 CO 0 o H 2 0‘” (.7. — H H {1 :7. fl Cflfi3-'C:H‘-(:+tifCL‘WD -7;;;“> CDfls-CZ:;f+t1—’CZ“WD (”{3_.C;.-<:+t3 +W + Ig’HYDRox‘IBHTYRATE NA” “A” H" J” ACETONE i A can AcETA TE 1‘on ATP PRODHCEb == 3 ATP +1 Name ANSWER KEY 2 __.___—_————.___—__—__—__—__ 2. (12 points total) (a) (6 points) Write out a balanced equation for the complete oxidation of Serine to carbon dioxide, bicarbonate and ammonium ion. SERlNE grep ;: same 4- fi+ + 550:. —* NHJW— BCO;+1H.10 +9- t. , --’ ' ‘ NHs f” ”03 STEP 2: H30 + col ——9 M + Haas +9. CH; . 5 4» - 5H OVERALL. seams + 3.0;z —-> NH+ +Hc05 +acoa+ H10 +1 (part b) (6 points) Write out a balanced reaction that shows how the bicarbonate and ammonium ions generated in serine oxidation can be converted into a product readily excreted by mammals. O . - u STEP t. H603 + 2mm; % NHi‘C‘NHa + H‘W— 34430 +9- STEP 2: H”r + Hco; _—> +1.10 + c0; 0 +9. n oveRAtu 2Hc03- 1- a. NHJ-—> NHaf’C‘NHa'.’ 3H,0 + cog. +2 3. (22 points total) S—Adenosyl—methionine (AdoMet) decarboxylase is a pyridoxal— phosphate (PLP) dependent enzyme. Draw out the complete structure of substrate and product (once is enough) and show the mechanism of this decarboxylation step. Use appropriate types of arrows to indicate electron movements, and draw out resonance forms that would stabilize your proposed intermediates. . ‘q __ HA8 of“) do” ca 35» ENZYME ENZWE '0” CCH‘R 2 . .. a +2. I/‘>H+ +1 ( l N—H «NH — NH 9‘: NH: ‘ u HM flu" $0“ ll 6”; . 6N?“ c~H ___, cH — NH - ca 2 CH R ?— CH3 N N’) \ OH \ 0H R @AfiOH CH3 0 ® ‘ |+/ ® [+1 fi/ LII—J 4-3 HO OH H +3 (4+2. H +1 NH; SAM PLP 5); col ' ENZYME CH3 +1 l CH; ENzVME NH: ', , -cu-R ? 0”“ AbeNINE ‘69: fiHif, g| CH3 0 H—gNH + +IH5'H H+ NH | Ha 0H H‘Q’j— CH é— CH (2—— EH 9—H ® '\’ m l C O” i \ ‘OH [:1 CH3 'Iq CH3 {1‘3 CH3 (9 I , H H H .l.‘ N “‘3 +2- +2 +2. Name ANswe'R JssLnfl __ 3 4. (26 points total) Ethanolamine ammonia—lyase from Clostridium is a bacterial enzyme that can convert 2-aminopropanol to propionaldehyde and ammonia. The reaction proceeds as shown below and is dependent on deoxyadenosyl—cobalamin (or deoxyadenosyl-BIZ). (a) (14 points) Draw out a mechanism showing how the enzyme converts Z—aminopropanol to the intermediate shown. Use appropriate types of arrows to indicate electron movements. Draw out just the part of the 812 coenzyme undergoing change! H53; (153 H ‘ . £5511 NH4+ _____> _ . ———-> and HQC E, CC,“ H 1U?" ' H OH; CH3'CH2'CHO H 2—aminopropanol intermediate final products DEOX‘I AbEN DS‘IL LEOXYADEN OSYL + , NH 4— a. ‘ 3 Leigh / +3 '0”; C Q5 OH \CO “I “"9 “H C . / \ \ 1r / H T / Co \ CH3 H + :1. + LEOXYABE’NOSYL i I DEW" AD?“ 0 3“ " +2. CH3 ‘ CH; +2 | . L cc”: \ V) II/ + ‘ o H / CO H CH3 H \ H (b) (2 points) Once the intermediate is generated, show how the final products, ammonia and propionaldehyde are formed. 3 H 0 |"“\ ___.., \ cH-cH—o—H cHg-oHae'crH + ”'4‘? (c) (10 points) How might our own cells metabolize propionaldehyde to an intermediate of the central metabolic pathways? Draw out a scheme for its metabolism (you may use either names or structures. Indicate any cofactors by name only. No electron pushing necessary here: +‘ +| +\ '0‘ NAM NABH o 00‘5” 0 u u “ , CHs'CHa” C’H —‘.—_> €443,014)” C’O’ —%_> CH3’ mg. C S “A ATP AMP PRDPIDNYLCOA PROPIONALDFH‘IDE PRoPuoNATE +1 +pP.‘ +u H33. ATP +\ CADP+PF +' ‘ o H H ?. H ° ll 6'1 I +| l cH—c-C‘SCOA é——-—— 00} —c-—ScaA succ: NY Leo A «-045me MMomwoA s- METH‘ILMA’WNVLCOA ...
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