細(xì)胞生物學(xué)11核糖體-在線瀏覽
2025-03-05 21:15本頁(yè)面
【正文】 epresentation. 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(duì)蛋白質(zhì)合成并沒(méi)有表現(xiàn)出 “ 全 ” 或 “ 無(wú) ” 的影響 。 ?在整個(gè)進(jìn)化過(guò)程中 rRNA的結(jié)構(gòu)比核糖體蛋白的結(jié)構(gòu)具有更高的保守性 。 r 蛋白質(zhì)的主要功能 ?對(duì) rRNA 折疊成有功能的三維結(jié)構(gòu)是十分重要的； ?在蛋白質(zhì)合成中 , 某些 r蛋白可能對(duì)核糖體的構(gòu)象起 “ 微調(diào) ” 作用； ?在核糖體的結(jié)合位點(diǎn)上甚至可能在催化作用中 , 核糖體蛋白與 rRNA共同行使功能 。 ?以多聚核糖體的形式進(jìn)行多肽合成 ， 對(duì) mRNA的利用及對(duì)其濃度的調(diào)控更為經(jīng)濟(jì)和有效 。 ?多聚核糖體的生物學(xué)意義 Visualizing transcription and translation (a) (b) Large subunit Small subunit mRNA Large subunit Small subunit Completed polypeptide (a) (b) (c) Polyribosomes (a) Schematic drawing of a polyribsome (polysome). (b) Electron micrograph of a grazing section through the outer edge of a rough ER cisterna. The ribosomes are aligned in loops and spirals, indicating their attachment to mRNA molecules to form polysomes. (c) Electron micrograph of metalshadowed polysomes isolated from reticulocytes engaged in hemoglobin synthesis. Most of these polysomes have between four and six ribosomes. mRNA + ① ② ③ In step 1, initiation of translation begins with the association of the 30S ribosomal subunit with the mRNA at the AUG initiation codon, a step that requires IF1 and IF3. The 30S ribosomal subunit binds to the mRNA at the AUG initiation codon as the result of an interaction between a plementary nucleotide sequence on the rRNA and mRNA. In step 2, a ternary (threemembered) plex consisting of formylmethionyltRNAIF2GTP bees associated with the mRNA30S ribosomal subunit plex acpanied by the release of IF3. In step 3, the 50S subunit joins the plex with the acpanying release of IF1, IF2, and the products of GTP hydrolysis (GDP and Pi). The initiation of protein synthesis in prokaryotes (a) (
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