分子生物学第七章遗传密码的利用Usingthegeneticcode.ppt
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1、Chapter 7Using the genetic code7.1 Introduction7.2 Codon-anticodon recognition involves wobbling7.3 tRNA contains modified bases that influence its pairing properties7.4 (There are sporadic alterations of the universal code)7.5 tRNAs are charged with amino acids by synthetases7.6 Accuracy depends on
2、 proofreading7.7 Suppressor tRNAs have mutated anticodons that read new codons7.8 The accuracy of translation7.9 tRNA may influence the reading frameStop codons are the three triplets (UAA, UAG, UGA) which terminate protein synthesis.7.1 IntroductionFigure 7.1 All the triplet codons have meaning: 61
3、 represent amino acids, and 3 cause termination (STOP).7.1 IntroductionFigure 7.2 The number of codons for each amino acid does not correlate closely with its frequency of use in proteins.7.1 IntroductionWobble hypothesis accounts for the ability of a tRNA to recognize more than one codon by unusual
4、 (non-GC, non-AT) pairing with the third base of a codon.7.2 Codon-anticodon recognition involves wobblingFigure 7.3 Third bases have the least influence on codon meanings. Boxes indicate groups of codons within which third-base degeneracy ensures that the meaning is the same.7.2 Codon-anticodon rec
5、ognition involves wobblingFigure 7.4 Wobble in base pairing allows G-U pairs to form between the third base of the codon and and the first base of the anticodon.7.2 Codon-anticodon recognition involves wobblingFigure 7.5 Codon-anticodon pairing involves wobbling at the third position.7.2 Codon-antic
6、odon recognition involves wobblingModification of DNA or RNA includes all changes made to the nucleotides after their initial incorporation into the polynucleotide chain.7.3 tRNA contains modified bases that influence its pairing propertiesFigure 7.6 All of the four bases in tRNA can be modified.7.3
7、 tRNA contains modified bases that influence its pairing propertiesFigure 7.7 Modification to inosine allows pairing with U, C, and A.7.3 tRNA contains modified bases that influence its pairing propertiesFigure 7.8 Modification to 2-thiouridine restricts pairing to A alone because only one H-bond ca
8、n form with G.7.3 tRNA contains modified bases that influence its pairing propertiesFigure 7.7 Modification to inosine allows pairing with U, C, and A.7.3 tRNA contains modified bases that influence its pairing propertiesFigure 7.9 Changes in the genetic code in mitochondria can be traced in phyloge
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