第五章克隆基因的表达.pptxVIP

;第一节 基因表达的基本条件;1、基因表达的基本过程;1、基因表达的基本过程;第一节 基因表达的基本条件;Transcription(转录): making an RNA copy of a DNA sequence 、 RNA polymerase opens the part of the DNA to be transcribed、 Only one strand of DNA (the template strand, antisense strand) is transcribed、 ;转录的具体过程;有效转录的基本条件;Operons are either inducible or repressible according to the control mechanism、 Seventy-five different operons controlling 250 structural genes have been identified for E、 coli、 Both repression and induction are examples of negative control since the repressor proteins turn off transcription、;; 启动子(promoter):在基因序列中,标志着转录起始的可被RNA聚合酶识别的位点(DNA区段),一般位于基因的上游。 终止子(terminator):位于基因的编码序列之外(一般在下游)的一段标志着转录停止的RNA聚合酶识别位点。;第一节 基因表达的基本条件;The Genetic Code To code for the 20 essential amino acids a genetic code must consist of at least a 3-base set (triplet) of the 4 bases、 If one considers the possibilities of arranging four things 3 at a time (4X4X4), we get 64 possible code words, or codons (a 3-base sequence on the mRNA that codes for either a specific amino acid or a control word)、 The genetic code was broken by Marshall Nirenberg and Heinrich Matthaei, a decade after Watson and Cricks work、 The genetic code consists of 61 amino-acid coding codons and three termination codons, which stop the process of translation、 The genetic code is thus redundant (degenerate in the sense of having multiple states amounting to the same thing), with, for example, glycine coded for by GGU, GGC, GGA, and GGG codons、 ;The genetic code;Messenger RNA (mRNA) is the blueprint for construction of a protein、 Transfer RNA (tRNA) is the truck delivering the proper amino acid to the site at the right time、 tRNA will form a cloverleaf structure due to plementary base pairing、 At the top of the large loop are three bases, the anticodon, which is the plement of the codon、 There are 61 different tRNAs, each having a different binding site for the amino acid and a different anticodon、 ;Ribosomes are the organelle (in all