遗传学课件（候阿澧）-10第十章 遗传物质的分子基础.pptVIP

第十章 遗传的分子基础 第二节 核酸的化学组成及结构分析 DNA紫外吸收 环状双链DNA复制方式 滚环复制：噬菌体ΦX174 D环复制：线粒体，质粒 θ-型复制：大肠杆菌DNA 滚环复制 1、以亲本链（＋链）为模板合成互补的环状负链，形成闭合环状的复制形RF1； 2、以成环滚环复制产生多个子代RF； 3、以RF的负链为模板进行滚环复制产生多拷贝正链单环。 电镜下显示的DNA的复制图象 3’-5’磷酸二酯键 DNA Structure Erwin Chargaff and Chargaff ’ rules A=T ; C≡G The Double Helix Watson and Crick ( 1953 ) X-ray diffraction photograph of the B form of purified DNA fibers. DNA双链构象改变因素： 1、核苷酸顺序 2、碱基组成 3、盐的种类 4、相对湿度 Tm ( melting temperature解链温度 ) The temperature at which a population of double-stranded nucleic molecules is half-dissociated into single strands. This is taken to be the melting temperature for that species of nucleic acid. Denaturation变性 and Renaturation复性 RNA 脱氧核糖——核糖；T——U 单链 3. 自身互补配对形成双链区。 rRNA ( ribosomal RNA ) mRNA (messenger RNA ) tRNA ( transfer RNA ) snRNA ( small nuclear RNA ) antisense RNA telomerase RNA primer ( in vivo ) DNA的复制 Replication ( Semiconservative Replication )半保留复制 ( Semidiscontinuous Replication )半不连续复制 The Meselson-Stahl experiment Enzymology酶学 of DNA Replication Helicase解旋酶 ( Strand Separation ) Single strand DNA-binding Proteins单链DNA结合蛋白 ( SSBs) Primerase引物酶 ( primer ) Ligase连接酶 Telomerase端粒酶 Topoisomerases II拓扑异构酶 ( relaxed DNA ) dCTP dTTP dATP dGTP * Proof of DNA as Genetic Material Transformation转化 in Bacteria ( Frederick Griffith . 1928 ) Characteristics of S.pneumoniae肺炎(链)双球菌 Strains When Grown on Blood Agar Medium Colony Morphology菌落形态 Type Appearance Size Capsule荚膜 Virulence毒性 II R Rough Small Absent Avirulent II S Smooth Large Present Virulent Colony Morphology Type Appearance Size Capsule Virulence IIIR Rough Small Absent Avirulent IIIS Smooth Large Present Virulent Reaction with Antiserum Prepared Against Type