mechanism - molecular and cell biology department at the ：机制的分子和细胞在生物学系

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1、UniversityofCapeTownDepartmentofMolecular&CellBiologyCourseCode:MCB2000FCourseName:IntrotoBiochemistryPaper:TheoryDate:13June2007@12h30No.ofpages:17Marks:137Time:3HoursVenue:NSLTAttachments:2pagesANSWERALLTHEQUESTIONSIntheinterestofeconomypleasewriteonbothsidesoftheexa

2、mscriptPleaseanswereachsectioninadifferentanswerbook.NotethatmultiplechoicequestionsaresubjectedtonegativemarkingSection1DrJerryRodrigues33MarksSectionA(Aminoacidsandproteins)1.Ahighlyidealizedtitrationof1moloffullyprotonatedcysteinewithsodiumhydroxideisshowninthefollo

3、wingfigure:(a)Writethethreeionizationreactions,withstructures,startingwithprotonatedcysteine.(4)(b)WhatregionsinthegraphcorrespondtoeachionizationstepieindicatethepKas(choosefromItoVII)?(3)(c)AtwhatpHvalueistheaveragenettchargeonthecysteineequalto-1(readoffthegraphorch

4、oosefromItoVII)?(1)(d)AtwhatpHvalueistheaveragenettchargeonthecysteineequalto-1/2(readoffthegraphorchoosefromItoVII)?(1)(e)AtwhatpHvalueistheaveragenettchargeonthecysteineequalto-2(readoffthegraphorchoosefromItoVII)?(1)17(f)Whatpointcorrespondstotheisoelectricpointofcy

5、steine(choosefromItoVII)?(1)(g)AtwhichpointisthepHequaltothepKavalueforthedissociationofthecarboxylgroup?(1)[12]2.Considerthefollowingcompound:(a)Whatkindofpeptidedoesthisstructurerepresent?(Forexample,dipeptide)(1)(b)Howmanypeptidebondsarepresent?(1)(c)Givethenamefort

6、heN-terminalaminoacid.(1)(d)GivethenamefortheC-terminalaminoacid.(1)(e)Usingthree-letterabbreviations,writethesequencefromN-toC-terminal.(2)[6]3.Thefigurebelowshowsthe13Cchemicalshiftsoccurringintitrationsoftheaminoacidlysine(structuretotherightoffigure).Matchthechemic

7、alshifts(curvesitovi)withthedesignatedcarbonatomsshownnexttothestructureofthelysinemolecule.(3)4.Whymustglycinebefoundatregularintervalsinthecollagentriplehelix?(2)175.Aredisulfidebridgesmostcommonlyfoundincytoplasmicproteinsorinsecretedproteins?Explainwhythisisthecase

8、.(3)6.Wehavelearntthatsomea-helicescanexhibitanamphipathicpropertywithhydrophilicandhydrophobicsides.(a)Canb-sheetsal