生物专业英语第三章有丝分裂.pptVIP

* 1. The nucleus and chromosomes * The cell nucleus is the main repository of genetic information.Within the nucleus are the chromosomes—tightly coiled strands of DNA and clusters of associated proteins.Long stretches of the continuous DNA molecule wind around these clusters of proteins, or histones, forming beadlike complexes known as nucleosomes. 细胞核是贮藏遗传信息的主要场所。细胞核里的是染色体－紧密盘绕成螺旋的DNA链和相关的成簇蛋白质。延伸长链DNA分子缠绕着成簇的蛋白质，或组蛋白，形成珠链状的核小体。 * More coiling and supercoiling produces a dense chromosome structure. Each long strand of DNA combine with histones and nonhistone proteins to make up the substance chromatin. 这些染色质进一步螺旋和超螺旋形成致密的染色体结构。每个长链DNA与组蛋白和非组蛋白一起构成染色质。 * A pictorial display of an organisms chromosomes in the coiled, condensed state is known as a karyotype. Karyotype reveal that in most cells all but sex chromosomes are present as two copies, referred to as homologous pairs. Non-sex chromosomes are called autosomes. 对生物这种致密的、双螺旋状态的图示我们称为染色体组。通过染色体组，我们发现除了性染色体外，大多数细胞的染色体成对出现，称同源染色体对。非性染色体称常染色体。 * Organisms whose cells contain two sets of parental chromosomes are called diploid; those with cells containing a single set of parental chromosomes are called haploid. 生物体内的细胞含有两套父母本染色体的称二倍体；含有单套染色体的称单倍体。 多倍体：带有两套以上同源染色体的细胞或个体。 * 2 The cell cycle * regular 有规律的 divide 划分 分离 repeat vt. 重复 in effect 实际上 single-celled 单细胞的 immortal [i?m?:tl] adj. 不死的；永恒的 multicellular [?m?lti?seljul?]多细胞的 muscle [?m?sl] n. 肌肉 nerve [n?:v] n. 神经 altogether 完全地 division 分开 * The cell cycle is a regular sequence in which the cell grows, prepares for division, and divides to form two daughter cells, each of which then repeats the cycle. Such cycling in effect makes single-celled organisms immortal. Many cells in multicellular organisms, including animal muscle and nerve cells, either slow the cycle or break out of it altogether. 在细胞生长过程中，细胞循环遵循固定程序，首先进行分裂准备，分裂成2个子细胞，子细胞再循环。此循环的存在让单细胞生物得以“长生不死”。多细胞生物中的许多细胞，包括动物肌细胞和神经细胞，要么细胞循环速度降低，要么全部从这个循环中脱离。 * The normal cell cycle consists