细胞核和染色体 1 课件.pptVIP

Solenoid—30nm fiber 超螺线管（Supersolenoid） (二)多级螺旋模型 DNA 核小体10nm 螺线管30nm 超螺线管300nm 染色单体700nm 压缩7倍 压缩6倍 压缩40倍 压缩5倍 DNA double helix 11nm 300nm 30nm 700nm 1400nm (三)染色体的骨架-放射环结构模型 The solenoid forms loops that attach to a scaffold of non-histone protein. 螺线管形成袢环，附着在非组蛋白支架上。 六、常染色质和异染色质 euchromatin and heterochromatin Under light microscopy, the light intensity zones are called euchromatin（常染色质）. Most of the active genes are found in euchromatin. Euchromatin 常染色质 Euchromatin is threadlike, delicate. Light-staining, less condensed; 30-nm fibers and looped domains Transcriptional activity Distributed throughout the nucleus 常染色质（伸展染色质 、功能性染色质）：无明显螺旋和盘曲、染色浅、功能上活跃。 Heterochromatin darkly staining and tightly coiled throughout the cell cycle genetically inactive. position effects， in a typical mammalian cell, approximately 10% of the genome is packaged into heterochromatins forming CEN and TEL Divided into two classes: Constitutive facultative chromatin plays important roles in cell living一、染色质是细胞生命活动的基础 the ratio of histons to DNA is 1:1 the ratio of non-histons to DNA is 0.6:1 the ratio of RNA to DNA is 0.1:1 二、染色质DNA 染色体与DNA Each unreplicated chromosome contains a single, continuous DNA molecule(每条未复制的染色体由1个DNA分子组成) （一） Genome（基因组） One copy of all the genetic information of an organism. 某一物种的细胞内储存于单倍体染色体中的遗传信息即构成该种的基因组。 Genome size-----Tab10-2 Genome size generally increases with an organism’s complexity. Some amphibian and plants have larger genome size than human. 物种的C值与其进化复杂性之间无严格对应关系。C值和生物结构或组成的复杂性不一致的现象称为C值悖论(C-value paradox)。 Species Genome size SV40 5 ×103bp E.coli 4.6×106bp Yeast 2×107bp Fruit fly 2×108bp Human 3×109bp (二) 染色质DNA类型 Protein-coding sequences（蛋白质编码序列） 编码rRNA, tRNA, snRNA和组蛋白的基因 repeated DNA(重复序列DNA) unassorted Interspersed DNA(未分类的间隔DNA) Protein-coding sequences蛋白质编码序列 ~25-50% of the protein-coding genes are solitar