第一章 基因.ppt

细菌如何分析呢？ 可以通过性导形成部分二倍体， 根据反式排列时的表型来确定顺反子。 By the 1950s, as the direct role that genes play in producing specific proteins became understood, Garrod began to acquire the reputation he currently enjoys—as the “father of chemical genetics”. Sickle-Cell Anemia J. Herrick (1910) first described sickle-cell anemia, finding that red blood cells (RBCs) change shape (form a sickle) under low O2 tension. E.A. Beet and J.V. Neel independently proposed (1949) that sickle-cell trait and disease were the result of a single mutant allele. Linus Pauling and coworkers (1949) used electrophoresis Hemoglobin is formed by four polypeptide chains, two molecules of the α polypeptide and 2 of the β polypeptide, each associated with a heme group V.M. Ingram (1956) found that the 6th amino acid of the β chain in sickle-cell hemoglobin is valine (no electrical charge) rather than the negatively charged glutamic acid in the β chain of normal hemoglobin 这样，一个操纵元中的一组基因就有两道控制开关，只有两道开关同时打开时，基因才能够转录。 乳糖启动子有两个CAP结合位点，一个是在 -70 到 -50(位点 I )，另一个是在 -50 到 -40(位点II)。 位点 I 包含一个反向重复序列，这似乎是大多数强结合位点的特征。位点II是一个很弱的结合位点，但是当cAMP—CAP复合物结合于位点I时，位点II结合cAMP-CAP复合物的能力显著提高。这也就是所谓协同效应(cooperativity)。一旦位点II被占据，RNA聚合酶就很快与 -35序列结合，然后再与-10序列结合。 遗传学方面，人们已经分离出两类使乳糖操纵元在无葡萄糖而有乳糖存在时也不能表达的突变体，一类位于编码CAP的cap(crp)基因上；另一类位于编码合成cAMP的腺苷酸环化酶 (adenylate cyclase) 基因cya上。细胞中CAP的合成是组成型的，因而也是相对稳定的。这样，具有正调控能力的cAMP—CAP复合物主要取决于cAMP的含量。腺苷酸环化酶位于细胞膜上。 第四节 基因工程 The Nobel Prize in Chemistry 1980 for his fundamental studies of the biochemistry of nucleic acids, with particular regard to recombinant-DNA for their contributions concerning the determination of base sequences in nucleic acids Paul Berg Walter Gilbert Frederick Sanger 一、酶的诱导现象 The influence of transcription controls can be very marked, and indeed has been observed since the turn of the century, but until recently the nature of these influences was not understood. In 1900, F. Dienert reported that the enzymes of