分子生物学-2.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,2020/7/19 Sunday,#,2026/11/9,分子生物学-2,关键术语,The,genome,(基因组),is the complete set of genes of an organism.Ultimately it is defined by the complete DNA sequence,although as a practical matter it may not be possible to identify every gene unequivocally solely on the basis of sequence.,The,transcriptome,(转录物组),is the complete set of genes expressed under particular conditions.It is defined in terms of the set of mRNA molecules that is present,and can refer to a single cell type or to any more complex assembly of cells up to the complete organism.,The,proteome,(蛋白质组),is the complete set of proteins.It should correspond to the transcriptome,although there can be differences of detail reflecting changes in the relative abundance or stabilities of mRNAs and proteins.,Proteins may function independently or as part of multiprotein assemblies.If we could identify all protein-protein interactions,we could define the total number of independent assemblies of proteins.,第3章 基因的数目,C-value,(C值),is the quantity of DNA in the genome(per haploid set of chromosomes).There is enormous variation in the range of C-values,from 10,11,bp for some plants and amphibians.,Nonrepetitive DNA(非重复序列DNA),shows reassociation kinetics expected of unique sequences.,Repetitive DNA,(重复序列DNA),behaves in a reassociation reaction as though many(related or identical)sequences are present in a component,allowing any pair of complementary sequences to reassociate.,第3章 基因的数目,第 1节 为什么基因组如此之大?,关键术语,第3章 基因的数目,第 1节 为什么基因组如此之大?,低等真核生物的单倍体DNA含量与形态学的复杂性相关，而在高等真核生物中，变化很大。下图为不同生物门类DNA含量的分布。,有花植物,鸟类,哺乳类,爬行类,两栖类,有骨鱼类,软骨鱼类,棘皮类,甲壳类,昆虫,软体动物,蠕虫,霉菌,藻类,真菌,革兰氏阳性细菌,革兰氏阴性细菌,支原体,蟾蜍和人类具有同样的最小量基因组DNA.但是我们认为人类的遗传复杂性显然要大于蟾蜍.,有些种系不同种生物之间的基因组DNA量差异极大而复杂性却没有大的不同,尤其是昆虫、两栖类和植物（可大于2个数量级），但鸟类和爬行类生物种间则基因组DNA量差异不大。,第3章 基因的数目,第 1节 为什么基因组如此之大?,一般来说，不同种系生物基因组大小的最底限度从原核生物至哺乳类随复杂性增加而增加.,基因所占的DNA远远大于编码蛋白质所需;,基因之间还存在非编码DNA序列,第3章 基因的数目,第 1节 为什么基因组如此之大?,The,C-value paradox,refers to the lack of a correlation between genome size and genetic complexity.,So it is not possible to deduce from the overall size of the genome anything about the number of genes.,问题：,基因组越大，是否所含的基因总数越多？,二层意思：1.独特基因增多；2.某些基因的拷贝树增加。,解决：1.最终依赖DNA测序；,2.真核基因组一般特性可通过变性DNA复性动力学进行评估。,变性DNA复性动力学可以将DNA分为,非重复序列DNA,和,重复序列DNA,二类,非重复序列DNA：,序列独特，半合子中只有一个拷贝,重复序列DNA：,不参与编码蛋白质。,中度重复序列DNA：序列较短，10-1000个拷贝，遍布基因组，与RNA前体高级结构形成有关。,高度重复序列DNA：序列很短（常100bp），数千拷贝以上，常成串排列。,第3章 基因的数目,第 1节 为什么基因组如此之大?,真核基因组不同序列组分的比例。非重复序列DNA的绝对含量随基因组增大而增加，但2,x,10,9,bp是个平台.,看来，,非重复序列DNA的绝对含量,与生物的复杂性似乎一致性更好。,第3章 基因的数目,第 1节 为什么基因组如此之大?,基因组序列的全长测序使我们弄清了几种生物的基因组大小和基因数目(,Arabidopsis,Drosophila,and man are estimated from partial data).致死基因座的数目是通过遗传学数据估测而来。,线虫,v,果蝇,第3章 基因的数目,第 2节 一些生物的基因总数,在果蝇,约20%的基因编码与基因表达和维持的蛋白,约20%编码酶蛋白,4000 in the yeast,and 9500 and 8000 in the worm and fly,respectively.,第3章 基因的数目,第 2节 一些生物的基因总数,果蝇基因组包括编码真核生物共有的基因、多细胞真核基因共有的基因和亚群生物（包括果蝇）更为特异的基因,。,第3章 基因的数目,第 2节 一些生物的基因总数,Natural selection is the force that ensures that useful genes are retained in the genome.The maintenance of a gene implies that it confers a selective advantage on the organism.One approach to the issue of gene number is to determine the number of essential genes by mutational analysis.Any mutation that is lethal is taken to identify a locus that is essential for the organism.（mutation,lethal genes,essential genes),第3章 基因的数目,第 3节 有多少必须基因？,Mycoplasma genitalium,2/3,and,E.coli,50%appear to be essential.Yeast,S.cerevisiae,12%are lethal,and another 14%impeded growth.,Questions:,Key questions that remain to be answered systematically are:What proportion of the total number of genes is essential,in how many do mutations produce at least detectable effects,and are there genes that are genuinely dispensable?Subsidiary questions about the genome as a whole are:What are the functions(if any)of DNA that does not reside in genes?What effect does a large change in total size have on the operation of the genome,as in the case of the related amphibians?,第3章 基因的数目,第 3节 有多少必须基因？,