《医学细胞生物学》本科课件09章 细胞核.ppt

Three key regions of a chromosome 随体 （3）次缢痕和随体： 次缢痕：近端着丝粒染色体（13，14，15，21，22）的 ... Nucleolus 形态结构： （电镜下） Summary of Chapter 8? The nucleus is a spherical, sometimes elongated structure that contains the genetic material, the DNA of the cell. The highly organized chromatin is enveloped by a nuclear membrane that contains numerous pores for the transport of large macromolecules and ribosomal subunits to the cytoplasm. The nuclear envelope is actually two parallel unit membranes with an intervening space. Ribosomes are often attached to the outside membrane and it is sometimes continuous with the rough ER. Functional aspects of nuclear It is the largest organelle in the cell and the place for genetic storage, replication and transcription. It is the control center of living activity and the hallmark to distinguish eucaryotic cells from prokaryotic ones. Chromatin consists of coiled DNA bound to basic proteins called histones and non-histone proteins. The degree of coiling of the chromatin varies during cell activity. From microscopic examination, two types of chromatin can be seen: 1) dark, dense heterochromatin and 2) light euchromatin. Cells with light nuclei / uncoiled chromatin are more active than those with condensed, dark nuclei. Lightly coiled DNA facilitates transcription because there is more surface area available. A DNA molecule is an enormously long, unbranched, linear polymer that can contain many millions of nucleotides arranged in an irregular but nonrandom sequence. The genetic information is contained in the linear order of the nucleotides.  Each DNA molecule is packaged in a separate chromosome, and the total genetic information stored in the chromosomes of an organism is said to constitute its genome. Each chromosome is formed from a single long DNA molecule. Each DNA molecule that forms a chromosome must contain a centromere, two telomeres and replicating origins. Most chromosomal DNA does not