武汉大学生命科学学院：《分子生物学》（英文版）Chapter 7 Translation

Chapter 7 Translation Translation is the conversion of the information in the nucleic acid sequence to polypeptides of a specific amino acid sequence

Chapter 7 Translation Translation is the conversion of the information in the nucleic acid sequence to polypeptides of a specific amino acid sequence

Crick的中心法则 DNA DNA 1957年 transcription Reverse 1970年 transcription RNA RNA translation Protein Protein

Crick的中心法则 DNA 1957年 transcription RNA translation Protein DNA Reverse 1970年 transcription Protein RNA

Section 1 The three roles of rna MRNA template for protein synthesis mRNA carries information from dna in a triple codon 1. The genetic code has redundancy(多余 性, so codon is degenerate(简并的)

一、 mRNA: template for protein synthesis mRNA carries information from DNA in a triple codon 1. The genetic code has redundancy (多余 性), so codon is degenerate (简并的). Section 1 The three roles of RNA

1954年,G. Gamey对破译密码首先提出了设想 4 nucleotides taken 1 at a time could specified only 4 different amino acid Two nucleotides taken at a time would permit only 4 or 16 amino acids to be specified any 3 adjacent nucleotides create 64 possibl codon(4 ), a number more than enough to specify 20 different amino acids

4 nucleotides taken 1 at a time could specified only 4 different amino acid. Two nucleotides taken at a time would permit only 42 or 16 amino acids to be specified; Any 3 adjacent nucleotides create 64 possible codon (43 ), a number more than enough to specify 20 different amino acids 。 1954年, G. Gamov 对破译密码首先提出了设想

2 Features of genetic codons Stop codon UAA UAG UGA Start codon AUG UGG p 1 8 amino acids have more than one codon called synonymous codons(同义密码子). Generally they differ only in their third position In all cases, if the third position is pyrimidine, the codons specify the same AA. In most cases. if the third position is a purine, the codons are also synonymous

2 Features of genetic codons Stop codon UAA UAG UGA Start codon AUG Met UGG Trp 18 amino acids have more than one codon, called synonymous codons (同义密码子). Generally they differ only in their third position. In all cases, if the third position is pyrimidine, the codons specify the same AA. In most cases, if the third position is a purine, the codons are also synonymous

Second position G 儿U UCU UAU UGU Phe ys UUC UCC UAC UGC UUA UCA UAA Stop UGA Stop A >Leu UCG AG Stop UGG Trp G CCU CAU CG CUC CAC CGC C Pro Ara CUA CCA CAA GA Gin CUG CCG CAG CGG G AUU ACU AAU AGU U Asn er AUC >lle ACC AAC AGC C Thr AUA ACA AAA AGA LyS AuG Met ACG AAG AGG ArgG GUU GCU GAU GGU U Asp GUC GCC GAC GGC val Ala Gly GGA Glu GAG

3 Effect of mutation The grouping of synonymous codons means that the effects of mutations are minimized Transitions(碱基转换) are where a purine is mutated into the other purine, or pyrimidine is mutated into other pyrimidine Transversions(碱基颠换) are where a purine changes to a pyrimidine or vice versa

The grouping of synonymous codons means that the effects of mutations are minimized. Transitions (碱基转换) are where a purine is mutated into the other purine, or pyrimidine is mutated into other pyrimidine . Transversions(碱基颠换) are where a purine changes to a pyrimidine or vice versa. 3 Effect of mutation

The effect of transition and transversion on specified amino acid Transition Transversion Third position no effect, over half no effect except Met, Trp Second position effect on AA effect on both species only AA species and type first position a similar type of AA, in few cases, no effect on AA species like Leu, Arg, Ser

The effect of transition and transversion on specified amino acid Transition Transversion Third position no effect, over half no effect except Met, Trp Second position effect on AA effect on both species only AA species and type first position a similar type of AA, in few cases, no effect on AA species like Leu, Arg, Ser

4 The universality of genetic codons Until recently, the standard genetic code was considered universal however. some deviations are found in mitochondria and some unicellular

4 The universality of genetic codons Until recently, the standard genetic code was considered universal, however, some deviations are found in mitochondria and some unicellular

Codon Usual Use Alternate Use Where alternate Use Occurs AGA Stop, Ser Some animal mitochondria. some AGG protozoans AUA Ile Met Mitochondria CGG Arg T Plant mitochondria CUU Thr Yeast mitochondria CUC CUA CUG AOU Ie Start(N-fMet) Some prokaryotes GUG OUG Leu UAA Stop u one protozoans UAG UGA Stor T Mitochondria, mycoplasmas Selenocysteine E colr 硒代半胱氨酸 Depends on context of message, other factor

硒代半胱氨酸