第二章 核酸和蛋白质 的结构和功能
第二章 核酸和蛋白质 的结构和功能
第一节、DNA--遗传的物质基础 一、 DNA是遗传物质的实验证据 1、肺炎球菌的转化现象 两种类型：光滑的S型 (Smooth)有毒 粗糙的R型(Rough)无毒 Griffith的转化实验
第一节 、DNA-------遗传的物质基础 一、DNA 是遗传物质的实验证据 1、肺炎球菌的转化现象 两种类型：光滑的S型（Smooth）有毒 粗糙的R型（Rough） 无毒 Griffith的转化实验
Strain of Strain of Colony Colony Cell type Effect Cell type Effect Capsule No capsule 静 ● ● Smooth(S) Live S strain Rough(R) Live R strain (a) (b) Effect e888。 Live R strain Effect Heat-killed Heat-killed S strain S strain Live S and R strains (c) (d) isolated from dead mouse Figure 2.2 Griffith's transformation experiments.(a)Virulent strain S S.pneumoniae kill their host;(b)avirulent strain R bacteria cannot infect successfully,so the mouse survives;(c)strain S bacteria that are heat-killed can no longer infect;(d)a mixture of strain R and heat-killed strain S bacteria kills the mouse.The killed virulent(S)bacteria have transformed the avirulent(R)bacteria to virulent(S). 转化：将无毒的R型菌在加热杀死的$型菌的作用下，转 化为有毒的$菌，称为转化
转化：将无毒的R型菌在加热杀死的S型菌的作用下，转 化为有毒的S菌，称为转化
1944年Avey重复了上述实验：确认转化物为 DNA S菌抽 提物 DNA酶处理 蛋白酶处理 不起转化作用 转化率不受影响 ↓ 1949年将Pr污染降至(0.02% DNA纯度越高，转化率越高
1944年Avery 重复了上述实验：确认转化物为 DNA S 菌 抽 提 物 DNA酶处理 蛋白酶处理 不起转化作用 转化率不受影响 1949年将Pr污染降至〈0.02% DNA纯度越高，转化率越高
2.T2噬菌体的侵染实验 1952年Hershey 的实验： Protein coat is DNA is labeled labeled specifically with 35S specifically with 32p Attachment of phage to host cel Removal of phage coats by blending Removal of phage coats by blending 3 plus unlabeled DNA 3 (a) (b) Figure 2.4 The Hershey-Chase experiment.Phage T2 contains genes that allow it to replicate in E.coli.Since the phage is composed of DNA and protein only.its genes must be made of one of these substances.To discover which,Hershey and Chase performed a two-part experiment.In the first part(a).they labeled the phage protein with 3S(blue).leaving the DNA unlabeled(black).In the second part(b).they labeled the phage DNA with 32P (red).leaving the protein unlabeled(black).Since the phage genes must enter the cell.the experimenters reasoned that the type of label found in the infected cells would indicate the nature of the genes.Most of the labeled protein remained on the outside and was stripped off the cells by blending(a). while most of the labeled DNA entered the infected cells(b).The conclusion was that the genes of this phage are made of DNA
2．T2噬菌体的侵染实验 1952年 Hershey 的实验：