Protein Metabolism

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1、ProteinMetabolismProteinsynthesis--Translation•TheprocessinwhichthegeneticinformationpresentinanmRNAmoleculespecifiesthesequenceofaminoacidsduringproteinsynthesis.以mRNA为直接模板，tRNA为氨基酸运载体,核蛋白体为装配场所，共同协调完成蛋白质生物合成的过程。也就是把mRNA的碱基排列顺序转译成多肽链中氨基酸的排列顺序。Threemajoradvancessetthestageforourpresentknowledge

2、ofproteinbiosynthesis•Thesiteofproteinsynthesis:ribosomes•Aminoacidareactivatedasaminoacyl-tRNA•ThegeneticcodeContents1.Thegeneticcode2.Proteinsynthesis3.Proteintargetinganddegradation1.ThegeneticcodeThegeneticcodewascrackedusingartificialmRNAtemplates•Acodonisatripletofnucleotidesthatcodesfora

3、specificaminoacid.•Nopunctuationbetweencodons•Initiationcodon:AUG•Terminationcodons(stopcodons,nonsensecodons):UAA,UAG,UGAReadingframeandOpenreadingframe•Areadingframeisacontiguous(邻近的)andnonoverlappingsetofthree-nucleotidecodonsinDNAorRNA.Thereare3possiblereadingframesinastrand.Areadingframeth

4、atcontainsastartcodonandastopcodoniscalledanopenreadingframe.Featuresofgeneticcode•commaless(连续性)•nonoverlapping(读码不重叠)•Universal(通用性)•Degenerate(简并性)•Wobble(摆动性)CodonandanticodonwobbleWobbleallowssometRNAtorecognizemorethanonecodon•Significance?Balancetherequirementsforaccuracyandspeed.密码子的特性•

5、无标点符号、读码不重叠、一定的防突变功能…AUGAAUAGAGAAGGCCGUC但如果是密码子甲天酪精谷赖甘丙…第三个碱基改变，硫冬氨氨氨氨氨氨氨酰酸酸酸酸酸酸氨基酸有可能不酸胺变。简并性、摆动性一个碱基突变,会如何？碱基丢失后续全变U一个碱基突变一个氨基酸改变TranslationalframeshiftingandRNAeditingSomemRNAsareeditedbeforetranslationRNAeditingofthetranscriptofthecytochromeoxidasesubunitIIgenefrommitochondriaofTrypanosomab

6、ruceiRNAeditingofthetranscriptofthegenefortheapo-lipoproteinB-100componentoflow-densitylipoproteinOverlappinggeneindifferentreadingframesarefoundinsomeviralDNAsGeneswithingenes.thecircularDNAofφX174Note:nonoverlappingincodonsPortionofthenucleotidesequenceofthemRNAtranscriptofgeneC,A,andKofφX174

7、2.ProteinsynthesisProteinsynthesistakesplaceintheribosome•TheribosomeisacomplexsupermolecularmachineBacterialribosomescontainsabout65%rRNAandabout35%proteinStructureofthebacterialribosome.greenrope:mRNA;shadesofgreen:tRNA•TherRNA