分子生物学2015-3-chromosome资料.pptVIP

Part II : Maintenance of the Genome;How are the Gene structures? How are DNA molecules that make up the chromosomes, which are extraordinarily long compared to the of the cell, packaged within the nucleus?;名词;A?gene?is a molecular unit of?heredity of a living?organism, it ? is a sequence of DNA (or RNA in virus) that codes for a?polypeptide (as in the case of the majority of genes) ?or for an RNA chain (as in the case of genes that code for tRNA and rRNA etc.) that has a function in the organism. 基因是可以转录成RNA所必需的全部DNA片段，分为编码区及调控区。 编码区：编码蛋白的基因中翻译成蛋白质的那部分核苷酸序列称可读框(open reading frame，ORF)。ORF始于起始密码子(initiation codon ATG/GTG), 终止于终止密码子(termination codon TAA/TAG/TGA)。 调控区：起调控作用的DNA序列，控制转录水平—启动子和终止子 (upstream and downstream);;prokaryotic cell, prokaryotes eukaryotic cell, eukaryotes Organisms with 2 copies of their chromosomes are diploid. Having one copy of the chromosome is called haploid. Polyploidy (having extra sets of chromosomes) is rare in animals but common in plants. ;Genome Size (the length of DNA associated with one haploid complement of chromosomes); ;开始转录;基因组较小，大多只有一条染色体，且结构简炼 基因密度高 蛋白质基因通常以单拷贝的形式存在；蛋白质基因内没有内含子 有重叠基因（Overlapping Genes） 操纵子(operon)是原核生物基因组的遗传组成基本特点 多顺反子mRNA (polycistronic mRNA)——包括不止一条基因编码区的mRNA，即一条mRNA链编码几种功能相关的蛋白质，各自含有独立的起始及终止密码子。也有单顺反子mRNA.;Operon is a functioning unit of genomic DNA containing a cluster of genes under the control of a single promoter. An operon is made up of several structural genes arranged under a common promoter and regulated by a common operator. Operator(操纵元件) is the site on DNA at which a repressor protein binds to prevent transcription from initiating at the adjacent promoter.;lacZ;Polycistronic mRNA (多顺反子mRNA);;PolⅡ core promoter;真核生物基因组DNA在细胞核内处于以核小体为基本单位的染色体结构中 真核基因组结构庞大 真核基因组中，编码序列只占整个基因组的很小部分，且复杂性高的生物基因密度低 含有大量重复序列 单顺反子mRNA(monocistronic) 基因不连续性 断裂基因（interrupted gene）、内含子(intron)、 外显子(exon);---- Two or more genes share or partially share the same DNA sequence （原核、真核中均存在