武汉大学生命科学学院：《分子生物学》（英文版）Part III：Expression of the Genome CHAPTER15 The Genetic Code

Molecular biology of the Gene 5/E - Watson et al. ( 2004) Part l: chemistry and genetics Part l: Maintenance of the Genome Part l: Expression of the Genome Part IV: Regulation Part v: Methods 3/2205 刻博来字 Wuhan Universit

Molecular Biology of the Gene, 5/E --- Watson et al. (2004) Part I: Chemistry and Genetics Part II: Maintenance of the Genome Part III: Expression of the Genome Part IV: Regulation Part V: Methods 3/22/05

Part III: Expression of the Genome Ch 12: Mechanisms of Transcription Ch 13: RNA Splicing Ch 14: Translation Ch 15: The Genetic Code

Part III: Expression of the Genome Ch 12: Mechanisms of Transcription Ch 13: RNA Splicing Ch 14: Translation Ch 15: The Genetic Code

Molecular Biology Course CHAPTER 15 The genetic code 隅来字 Wuhan University

CHAPTER 15 The Genetic Code •Molecular Biology Course

The Central Dogma Transcription CDNALRNA→→ Protein Translation Replication 1, Genetic information transfer from polynucleotide chain into polypeptide chain. 2. Take place in ribosomes. 3. tRNAs recognize codons

DNA RNA Protein Replication Transcription Translation The Central Dogma 1. Genetic information transfer from polynucleotide chain into polypeptide chain. 2. Take place in ribosomes. 3. tRNAs recognize codons

CHATER 15 The Genetic Code Topic 1: THE CODE IS DEGENERATE Codon: degenerate Anticodon: wobble 劣溪字 Wuhan University

Topic 1: THE CODE IS DEGENERATE CHAPTER 15 The Genetic Code Codon: degenerate Anticodon: wobble

second position G Many amino uu pe ucc ser/ uAc uGc Cys acids are UCU UGU U UCA UAA' stopUGA stop UUG UCG UAG' stop UGG Trp specified bv y more than CUU CCU CAU CGU U CUC CCC CAC Pro cione codon- CUA CCA 5oc苏 CUG CCG CAGGIn CGG G degeneracy AU ACU AUC lleACC A~日(简并性 AUA . Codons UGt Met ACG AAG Lys A ArgG GU GCU GAU GGU specifying GUC GCC GAc Asp GGC / ins I the same GCA GAA GAA Glu GUG GCG GAG G amino acid Chain-terminating or nonsense" codons t Also used in bacteria to specify the initiator formy -Met-tRNA Met are callled TABLE 15-1 synonyms The Genetic code 同义密码子)

Many amino acids are specified by more than one codon￾degeneracy (简并性). Codons specifying the same amino acid are called synonyms (同义密码子). TABLE 15-1 The Genetic Code

Coding role #1 1.Often,when the first two nucleotides are identical. the third nucleotide can e either C or U without changing the code. A and G at the third position are interchangeable as well 2. Transition in the third position of a codon specifies a same amino acid Transversion in this position changes the amino acid about half the time

Coding role #1 1.Often, when the first two nucleotides are identical, the third nucleotide can be either C or U without changing the code. A and G at the third position are interchangeable as well. 2.Transition in the third position of a codon specifies a same amino acid. Transversion in this position changes the amino acid about half the time

CH3 0-C-C-C-CH 内H NH H CH acceptor cIna ssm o Twc ssem stem CCCCc.A ATC CCcu°A GGGGGTC loop CGGGrC . anticodon anticodon elocon mRNA3匚@uc—3 mRNA3匚cuc5 CUG CUC Figure 15-1 Codon-anticodon pairing of two tRNA Leu moleculars

Figure 15-1 Codon-anticodon pairing of two tRNA Leu moleculars CUG CUC

Code degeneracy explains how there can be great variation in the AT/Gc ratios in the dna of various organisms without large changes in the proportion of amino acids in their proteins

Code degeneracy explains how there can be great variation in the AT/GC ratios in the DNA of various organisms without large changes in the proportion of amino acids in their proteins

Perceiving Order in the Makeup of the Code o 1. The genetic code evolved in such a way as to minimize the deleterious effects of mutations I 2. Code degeneracy may serve as a safety mechanism to minimize errors in the reading of codons

Perceiving Order in the Makeup of the Code 1. The genetic code evolved in such a way as to minimize the deleterious effects of mutations. 2. Code degeneracy may serve as a safety mechanism to minimize errors in the reading of codons. The Code Is Degenerate