細胞生物學(xué)11核糖體(完整版)
【正文】 ome relative to the mRNA. Translocation is acpanied by the movement of the deacylated tRNA and peptidyltRNA into the E and P sites, respectively. In step 4, the deacylated tRNA leaves the ribosome, and a new aminoacyltRNA enters the A site. (b) Peptide bond formation and the subsequent displacement of the deacylated tRNA. 三、 RNA在生命起源中的 地位及其演化過程 ? 生命是自我復(fù)制的體系 ? DNA代替了 RNA的遺傳信息功能 ? 蛋白質(zhì)取代了絕大部分 RNA酶的功能 Evolution of RNAs that can direct Protein synthesis Evolution of new enzymes that create and make RNA copies from it Question Discussing the following: During the evolution of life on the earth, RNA has been demoted from its glorious position as the first selfreplicating catalyst. Its role now is as a mere messenger in the information flow from DNA to protein. 生命是自我復(fù)制的體系 ?三種生物大分子，只有 RNA既具有信息載體功能又具有酶的催化功能。 (a) Important Binding Sites on the Prokaryotic Ribosome This model of ribosome structure shows the A (aminoacyl) and P (peptidyl) sites as cavities on the ribosome where charged (amino acidcarrying) tRNA molecules bind during polypeptide synthesis. The more recently postulated E (exit) site is the site from which discharged tRNAs leave the ribosome. The mRNAbinding site binds a particular nucleotide sequence near the 5’ end of the mRNA, placing the mRNA in the proper position for the translation of its first codon. (a) The diagrammatic representation of a ribosome. The pair of horizontal dashed lines indicate where the mRNA molecule lies. (b) A more realistic representation. The binding sites are all located at or near the interface between the large and small subunits. (b) 在蛋白質(zhì)合成中肽酰轉(zhuǎn)移酶的活性研究 ? 核糖體蛋白 ? 在核糖體中 rRNA是起主要作用的結(jié)構(gòu)成分 ? r 蛋白質(zhì)的主要功能 核糖體蛋白 ?很難確定哪一種蛋白具有催化功能： 在 E. coli中核糖體蛋白突變甚至缺失對蛋白質(zhì)合成并沒有表現(xiàn)出 “ 全 ” 或 “ 無 ” 的影響 。 E. coli (a) 核糖體小亞單位中的部分 r蛋白與
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