《分子生物学》第15章 遗传编码（英文教学课件）非AI生成.ppt

CHAPTER15

TheGeneticCode*DecipheringCell-freetranslationofartificialRNAs(Nirinberg,1961)Thetripletbindingassay(Nirinberg,1964)tRNA和氨基酸、核糖体及三联体的结合是特异的上述结合的复合体大分子是不能通过硝酸纤维滤膜的微孔，而tRNA-氨基酸的复合体是可以通过的。poly(U)---UUU---polyphenylalaninepoly(C)---CCC---polyprolinepoly(A)---AAA---polylysinepoly(G)---didnotworkbecauseofthecomplexsecondarystructureAttempttoDecipher:1954,GeorgeGamow*ThreerulesgovernthegeneticcodeFeatures:ThecodeisdegenerateWobbleintheanticodonThecodeisnearlyuniversalSuppressormutationscanresideinthesameoradifferentgene*Thefirstruleholdsthatcodonsarereadina5’to3’direction.Thesecondruleisthatcodonsarenonoverlappingandthemessagecontainsnogaps.Thefinalruleisthatthemessageistranslatedinafixedreadingframe,whichissetbytheinitiationcodon.*ThreerulesgovernthegeneticcodeFeatures:ThecodeisdegenerateWobbleintheanticodonThecodeisnearlyuniversalSuppressormutationscanresideinthesameoradifferentgene*degeneracyManyaminoacidesarespecifiedbymorethanonecodon,thephenomenoncalleddegeneracy.*WobbleWobbleconceptThebaseatthe5’endoftheanticodonisnoasspaticallyconfinedastheothertwoallowingittoformhydrogenbondswithanyofseveralbasedlocatedatthe3’endofacodon,withpairingrestricttothoseontherighttable*UniversalityThestandardcodonsaretrueformostorganisms,butnotforall.CodonPreference*ReversetheharmfulmutationsbyasecondgeneticchangeSuppressormutationscanresideinthesameoradifferentgene

Reverse(back)mutations:changeanalterednucleotidesequencebacktoitsoriginalarrangement.Suppressormutations:suppressthechangeduetomutationatsiteAbyproducinganadditionalgeneticchangeatsiteB.(1)Intragenicsuppression(2)Intergenicsuppression*Figur