普通生物学课件第二章微生物的形态和构造（一）原核微生物.ppt

星空8538的个人中心 Donation of DNA. This image is from: :82/hurlbert/micro101/pages/Chap9.html ◆Certain types of bacteria can donate a piece of the their DNA to a recipient cell. The recombination is the bacterial equivalent of sexual reproduction in eukaryotes. Note that the entire DNA is not usually transferred, only a small piece. ◆Scattered within bacterial cytoplasm are numerous small loops of DNA known as plasmids. ◆Plasmids, small DNA fragments, are known from almost all bacterial cells. Plasmids carry between 2 and 30 genes. Some seem to have the ability to move in and out of the bacterial chromosome. 可自我复制，稳定遗传。对生存不是必要的。复制与染色体分开，但同步进行。 不同质粒携带不同遗传信息。 无质粒细菌可通过接合、转化、转导等方式获得，不能自发产生。 质粒的种类：细菌抗药性因子、大肠杆菌的F因子。 质粒应用:基因工程，体外重组. Diagram of bacterial conjugation. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates () and WH Freeman (), used with permission. ◆ 细胞膜内除核质体外的一切透明、胶状、颗粒状物质可总称为细胞质。主要成分有：核糖体、贮藏物、各种酶类、中间代谢物及质粒等,少数细菌还存在有羧化体、伴胞晶体或气泡等 ◆ Cytoplasmic Structures(a). Nucleoid - An area of concentrated DNA with no nuclear membrane. The DNA is single circular, double stranded without proteins. (b). Ribosomes - 30S and 50S to form a 70S complex. (c). Plasmids - Extrachromosomal loops of DNA, some code for drug resistance, toxins and other factors. ◆Bacteria lack a nuclear membrane and membrane-bound organelles. Biochemical processes that normally occur in a choloroplast or mitochondrion of eukaryotes will take place in the cytoplasm of prokaryotes. 原核生物的核糖体常以游离状态存分布细胞质中，在生长旺盛的细胞中，核糖体常成串排列，称多聚核糖体(polyribosome)。核糖体之间靠mRNA连接。而真核生物细胞的核糖体既能够以游离状态存于细胞质中,也可以结合到内质网上,颗粒的沉降系数为80S(60S+40S)。这是原核细胞与真核细胞核糖体的区别。 Table 12. Some inclusions in bacterial cells.  Inclusions Often contained in the cytoplasm of procaryotic cells is one or another of some type of inclusion granule. Inclusions are distinct granules that may occupy a substantial part of the cytoplasm. Inclusion granules are usually reserve materials of some sort. For