第三节分子生物学的中心法则TheCentralDogmaofMolecularBiology.ppt

1、Chapter 10 Gene Mutation,Severe Acute Respiratory Syndrome (SARS),H1N1 流感病毒,流感的启示,问题,1、为什么每一次大流行的流感病毒的类型都不一样？2、为什么如此猖狂和恐怖的流感病毒不能像天花病毒一样被“消灭”？为什么不能通过接种疫苗进行有效的预防？,血凝素（HA）,神经氨酸酶（NA），,SARS的S蛋白质和M蛋白质的变异点位达到31个，这说明SARS病毒具有极强的变异能力，这意味着研究SARS疫苗可能会同研究流感疫苗一样困难重重,1、What Are Mutations?,4、What Causes Mutations?,

2、3、Consequences of Mutations,5、How to Detect the Gene Mutation?,2、 Features of Gene Mutantion,OUTLINE,Chapter 10 Gene Mutation,1、What Are Mutations?, Any heritable change in the DNA（RNA） sequence of an organism is a mutation. Mutations can be divided into three main types1. Chromosome mutations（染色体突变

3、）2. Genome mutations（基因组突变）3. gene mutations（基因突变）Relatively small changes in DNA structure that occur within a particular gene, Gene mutation（基因突变）: changes in one or a few nucleotides. point mutation(点突变) are mutations of a single nucleotide.Includes the deletion, insertion, or substitution in a g

4、ene.（碱基的增加及缺失、碱基替换）,替换,增加及缺失,A transition(转换) is a change of a pyrimidine (C, T) to another pyrimidine or a purine (A, G) to another purineA transversion(颠换) is a change of a pyrimidine to a purine or vice versa,转换和颠换的相互关系示意图,Mutations may also involve the addition or deletion of short sequences of

5、DNA,5 AACGCTAGATC 33 TTGCG ATCTAG 5,5 AACGCTC 33 TTGCGAG 5,Deletion of four base pairs,Addition of four base pairs,Mutations Due to Trinucleotide Repeats（dynamic mutation）,Mutations happen regularlyMutation rateForward & backward(or reverse) mutationMultiple orientations Beneficial & deleteriousMuta

6、tion similarity between the related species,2、 Features of Gene Mutantion,Mutations happen regularly,Therefore, the mutation can be passed on to future generations,The size of the patch will depend on the timing of the mutation,The earlier the mutation, the larger the patch,An individual who has som

7、atic regions that are genotypically different from each other is called a genetic mosaic,Therefore, the mutation cannot be passed on to future generations,Mutation rate,The frequency with which a particular mutation appears in a population.,Forward & backward(or reverse) mutation(正突变&回复突变),A,a,forwa

8、rd,reverse,通常从一个野生型基因变成突变性的频率总是高于回复突变率，如何解释？,一突变型回复成野生型，可能机制是什么？（预习基因重组）,A,a1,a2,a3,Multiple orientations（多向性）,Beneficial & deleterious,Harmful,Almost all mutations are neutral,beneficial,Some terms,lethal mutation（致死突变）: Mutation that eventually results in the death of an organism carrying the muta

9、tion.neutral mutation（中性突变）: A mutation that has no selective advantage or disadvantage.conditional mutation（条件突变）: A mutation that is only expressed under certain environmental conditions.,Mutation similarity between the related species（突变的平行性）,+,3、Consequences of Mutations,Mutations in the coding

10、sequence of a structural gene (can have various effects on the polypeptide),Mutations in Non-coding Sequences(affect gene expression),insert,3、Consequences of Mutations- coding sequence,3、Consequences of Mutations- coding sequence,Silent mutations (or silent) mutation（同义突变）: base substitutions that

11、do not alter the amino acid sequence of the polypeptide. Missense mutations(错义突变) are those base substitutions in which an amino acid change does occur. Nonsense mutations （无义突变）: are those base substitutions that change a normal codon to a termination codon. Frameshift mutations （移码突变）: involve the

12、 addition or deletion of nucleotides in multiples of one or two.,3、Consequences of Mutations- coding sequence,如果你所研究的基因发生了突变，你将如何从遗传学角度判断他是错义突变、无义突变还是移码突变？,3、Consequences of Mutations- Noncoding sequence,为什么操纵子区（oprator）和启动子(promoter)突变总是顺式显性和反式隐形突变？而编码阻抑蛋白基因突变，则是顺式还是反式显性呢？,Mutations can occur spont

13、aneously or be inducedSpontaneous mutations(自发突变)Result from abnormalities in cellular/biological processesfor example： Errors in DNA replicationInduced mutations （诱发突变）Caused by environmental agentsAgents that are known to alter DNA structure are termed mutagensThese can be chemical or physical agents,4、What Causes Mutations?,1、What Are Mutations?,4、What Causes Mutations?,3、Consequences of Mutations,2、 Features of Gene Mutantion,Summary,