8 Structures of Nucleic acids

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1、StructureStructureofNucleicAcidsStructureofNucleicAcidsXianmingDENGSchoolofLifeSciences,XiamenUniversity2013-10-28Agenda: An OverviewDNA Structure RNAStructureRNAStructureDNAStructureDNAStructure1. DNA StructureThe Double Helix •Thebaseshydrogenbondtoeachotheri

2、naspecificway:AhyygdrogenbondstoT,,andGhyygdrogenbondstoC,,forminggasetofcomplementary base pairs: The Double Helix •ThisallowstwoseparatestrandsofsugarThisallowstwoseparatestrandsofsugar-phosphatebackbonestophosphatebackbonestorunalongsideeachother,heldtogetherb

3、ythehydrogenbondsbetweenthecomplementarybasepairs:•The“ladder-like”structurefoldsinonitselftoformadoublehelix,withthebasesontheinsideandthesugarthebasesontheinsideandthesugar-phosphatebackboneontheoutside:Minor and Major GroovesThe Major Groove Is Rich in Chemica

4、l Information•AiilA principaldddecodiing mechhianism reliesupontheabilityofaminoacidsidechainstoprotrudeintothemajorgrooveandtorecognizeandbindtospecificDNAsequencesThe Double Helix Exists in Multiple Conformations•Bform–StandardDNAdoublehelixunderphysiologicalco

5、nditions•Zform–laboaboatoyaoay,ratoryanomaly,•LeftHanded•RequiresAlt.GC•HihSlt/ChHighSalt/ChargeneuttliralizationSugar “Pucker”DNA Backbone Flexibility•MultipleDegreesofRotationalFreedomRotationalFreedomGlycosidicBond ConfigurationsCertain DNA Sequences Adopt Unu

6、sual Structures（回文结构）（镜像重复）Hairpin formation in a palindromicDNA strand.Cruciformformationoccurswhentwostrandsareinvolved（十字形的）Structural basis for DNA structures containing three or four strandsHoogstein Pairing in Base TriplesTriple helix or H-DNARNAStructureRN

7、AStructure1.RNA Structure  Comparison of RNA with DNA ContainsriboseratherContainsriboseratherthan2-deoxyriboseContainsuracilinplaceofthymine.Usuallysingle-strandedRNA Contains Ribose and Uraciland Is Usually Single-StrandedExceptforthecaseofcertainviruses,RNA

8、isnotthegeneticmaterialanddoesnotneedtobecapableofservingasatemplateforitsownreplication.servingasatemplateforitsownreplication.RNA species:mRNA(messenger),t-R