核酸、染色體及基因-文庫(kù)吧資料
2025-01-25 02:43本頁(yè)面
【正文】 端粒起到細(xì)胞分裂計(jì)時(shí)器的作用，端粒的核苷酸每復(fù)制一次減少 50100bp，其復(fù)制要靠具有反轉(zhuǎn)錄酶性質(zhì)的端粒酶（ telomerase）來(lái)完成，正常體細(xì)胞缺乏此酶，故隨細(xì)胞分裂而變短，細(xì)胞隨之衰老。 Top view Side view 連接 DNA（ Linker DNA） the linker DNA between the nucleosome cores varies between less than 10 and more than 100 bp, but is normally around 55 bp. The nucleosomal repeat unit is hence around 200 bp. 30nm纖絲 ? 核小體將進(jìn)一步組裝成更高級(jí)別的空間結(jié)構(gòu) , 稱為 30 nm fiber 或螺線管； ? 左手螺旋 ? 六個(gè)核小體每圈 高級(jí)結(jié)構(gòu) On the largest scale, chromosomal DNA is anized into loops of up to 100 kb in the form of the 30 nm fiber, constrained by a protein scaffold, the nuclear matrix. The overall structure somewhat resembles that of the anizational domains of prokaryotic DNA. 真核生物染色體的結(jié)構(gòu)特征 ? 有絲分裂染色體 ? 著絲粒 ? 端粒 ? 異染色質(zhì) ? 常染色質(zhì) ? CpG 甲基化 ? 特殊的染色體 有絲分裂染色體 1. Replication occurs during S phase 2. G1 and G2 are intervals to provide additional time for cell growth. Cell division. A parental cell in G1 has two copies of each chromosome (2n), one maternal (red) and one paternal (blue). Chromosomes are replicated during the S phase, giving a 4n chromosomal plement. At the midpoint of mitosis (metaphase), the replicated chromosomes are aligned and held in position by the mitotic apparatus. The two identical chromatids posing each replicated chromosome then move to opposite ends of the cell, the nuclear membrane reforms around each set of chromosomes, and finally cytokinesis splits the cell into two geically identical daughter cells. 著絲粒、端粒 著絲粒 （ Centromeres） 著絲粒是分裂中期兩條姊妹染色單體相連的緊縮區(qū)域，是一種與紡錘體相連的部位。 DNA結(jié)合蛋白 ? 原核生物的染色體中環(huán)型的 DNA由于大量的 DNA結(jié)合蛋白相互作用而進(jìn)一步受到束縛，進(jìn)而包裝形成類(lèi)核。 Bacterial DNA is pacted in a structure called the nucleoid, which occupies a large fraction of the bacterial cell‘s volume. DNA結(jié)構(gòu)域 ?將大腸桿菌 DNA與大多數(shù)結(jié)合蛋白分離開(kāi)來(lái)，在電子顯微鏡下可觀察到由 50－ 100個(gè)環(huán)或結(jié)構(gòu)域組成，這些環(huán)或結(jié)構(gòu)域的末端與細(xì)胞膜上蛋白質(zhì)連接而固定 。 1變化 II型拓?fù)洚悩?gòu)酶 纏繞數(shù)以 177。 ? 核酸定量 吸光值（ Extinction coefficient ） ? 1 mg/ml dsDNA: A260 =
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