清华大学：《分子生物学》（英文版）Chapter 7 Using the genetic code

Chapter 7 Using the genetic code 莘大

Chapter 7 Using the genetic code

7. 1 Introduction 7.2 Codon-anticodon recognition involves wobbling 7. 3 tRNA contains modified bases that influence its pairing properties 7. There are sporadic alterations of the universal code) 7.5 tRNAS are charged with amino acids by synthetases 7.6 Accuracy depends on proofreading 7.7 Suppressor tRNAs have mutated anticodons that read new codons 7. 8 The accuracy of translation 7.9 tRNA may influence the reading frame 消当

7.1 Introduction 7.2 Codon-anticodon recognition involves wobbling 7.3 tRNA contains modified bases that influence its pairing properties 7.4 (There are sporadic alterations of the universal code) 7.5 tRNAs are charged with amino acids by synthetases 7.6 Accuracy depends on proofreading 7.7 Suppressor tRNAs have mutated anticodons that read new codons 7.8 The accuracy of translation 7.9 tRNA may influence the reading frame

7.1 Introduction Stop codons are the three triplets qUAA, UAg UGA) which terminate protein synth hesis 消当

Stop codons are the three triplets (UAA, UAG, UGA) which terminate protein synthesis. 7.1 Introduction

7.1Introduction U Leu/ UcaS se, UAg y/UGU Phe UCl UAU UCC UGC UAA STOP ∪ GA STOP UCG UGe Tr Figure 7. 1 All the CG triplet codons have CUC LeU cCA CCCl P CAULHIS CGCLArg CAC CUA CAA GIn CG meaning: 61 CUG cCG CAG CGG represent amino AUA ACA// AACrAsn Ser A ACI AAU AUC\ le ACC GC acids. and 3 cause AUG Met ACGAAC AA凡 ys AGGI9 termination (STOP) GA GGI GUC GGC GUA GG G Glu GGG 消当

Figure 7.1 All the triplet codons have meaning: 61 represent amino acids, and 3 cause termination (STOP). 7.1 Introduction

7.1Introduction Per cent of residues in protein 10 eur 8 Ala Glu y ser● Figure 7.2 The 6 Lys● Val le● h AS number of codons Pro: Arg● A for each amino acid Pheb does not correlate Met. His● closely with its Tm frequency of use in 4 5 proteins Number of codons 消当

Figure 7.2 The number of codons for each amino acid does not correlate closely with its frequency of use in proteins. 7.1 Introduction

7.2 Codon-anticodon recognition involves wobbling Wobble hypothesis accounts for the ability of a trna to recognize more than one codon by unusual (non-G C non-a T) pairing with the third base of a codon 消当

Wobble hypothesis accounts for the ability of a tRNA to recognize more than one codon by unusual (non-G C, non-A T) pairing with the third base of a codon. 7.2 Codon-anticodon recognition involves wobbling

7.2 Codon-anticodon recognition involves wobbling UUU UCU UUC UCC UAC JGC UUA UCA UGA UUG UCG UAG UGG CCU CAU CGU CUC CCC CGC Figure 7.3 Third bases CAA CGA CUG CCG CAG CGG have the least influence A儿U ACU 凸凸 AGU AUC ACC AAC AGC on codon meanings AUA ACA AAA AGA AUG AGG Boxes indicate groups GUU GCU GAU GGU GUC GCC GGC GUA GCA of codons within which GGA GUG GCG GAG GGG third-base degeneracy Third base relation ship Third bases Number with same of codons ensures that the meaning meaning is the same third base irrelev ant U,C, A,G 32 purines differ rom pyrimidines Aor G 10 unique U CA definitions n 消当

Figure 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 recognition involves wobbling

Standard base pairs occur at all positions 7.2 Codon-anticodon recognition involves wobbling Cytosine H Guanine Figure 7. 4 Wobble in base pairing allows G-U Uracil pairs to form between Adenine the third base of the G-U wobble pairing occurs only at third codon position codon andand the first base of the anticodon 消当

Figure 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 wobbling

7.2 Codon-anticodon recognition involves wobbling Base in First Base(s)Recognized Position of in Third position of Anticodon Codon A or G CAG G only U only r Figure 7.5 Codon-anticodon pairing involves wobbling at the third position 消当

Figure 7.5 Codon-anticodon pairing involves wobbling at the third position. 7.2 Codon-anticodon recognition involves wobbling

7.3 tRNA contains modified bases that influence its pairing properties Modification of dna or rna includes all changes made to the nucleotides after their initial incorporation into the polynucleotide chain 消当

Modification 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 properties