第8篇 细胞核.pptVIP

* * * * 染色单体横断面 * * * * * * * * * * * * Figure 6-41. Transcription from tandemly arranged rRNA genes, as seen in the electron microscope. The pattern of alternating transcribed gene and nontranscribed spacer is readily seen. A higher-magnification view was shown in Figure 6-9. (From V.E. Foe, Cold Spring Harbor Symp. Quant. Biol. 42:723 740, 1978. cells of the frog Xenopus contain about 600 rRNA gene copies per haploid genome in a single cluster on one chromosome (Figure 6–41). * * * * * * * * * * * * 上：扫描电镜 下：透射电镜 * * * 用高盐溶液、非离子去垢剂和核酸酶去除大部分核物质，只有核孔复合体和核纤层存留，但仍然能维持核的轮廓 * * * * K+ 、 Ca2+、Mg2+、Cl-等离子 分子量小于5KD的小分子，如水、单糖、双糖、氨基酸、核苷和核苷酸等。 * * * * * * * * Figure 4-21. A comparison of extended interphase chromatin with the chromatin in a mitotic chromosome. (A) An electron micrograph showing an enormous tangle of chromatin spilling out of a lysed interphase nucleus. (B) A scanning electron micrograph of a mitotic chromosome: a condensed duplicated chromosome in which the two new chromosomes are still linked together (see Figure 4-22). The constricted region indicates the position of the centromere. Note the difference in scales. (A, courtesy of Victoria Foe; B, courtesy of Terry D. Allen.) * * * * * * * * * * * * * Figure 4-23. Nucleosomes as seen in the electron microscope. (A) Chromatin isolated directly from an interphase nucleus appears in the electron microscope as a thread 30 nm thick. (B) This electron micrograph shows a length of chromatin that has been experimentally unpacked, or decondensed(unfold partially), after isolation to show the nucleosomes. (A, courtesy of Barbara Hamkalo; B, courtesy of Victoria Foe.) 铺展的核仁染色质标本 ※概念*：间期，rDNA是从染色体上伸出的DNA袢环，袢环上的rRNA基因成串排列，通过转录产生rRNA，组织形成核仁，因此称为核仁组织者。 功能：组织核仁的形成 核仁组织者（nucleolus organizer） 致密纤维 组分 颗粒组分 纤维中心 (二)致密纤维组分 核仁内电子密度最高的区域，呈环形或半月形包围浅染的纤维中心。 主要成分： 正在转录的rRNA分子 核糖体蛋白 某些特异性的RNA结合蛋白 致密纤维 组分 颗粒组分 纤维中心 (三)颗粒成分 呈致密的颗粒，密布于纤维骨架之间，或围绕在纤维组分的周围 主要成分：处于不同加工、成熟阶段的核糖体亚基前体 上述三种组分存在于核仁基质（nucleolar matrix）中 核仁