southeast university genetic center 第六节 细胞核 Cell Nucleus

细胞核的功能 The functions of cell nucleus Organize genes into chromosomes. Transport regulatory factors and gene products via nuclear pores. Produce messages ( mRNA) that code for proteins. Assemble ribosomes in the nucleolus Organize the uncoiling of DNA to replicate

真核细胞核 (Nucleus of a Eukaryotic Cell ) 真核细胞核 核被膜 (Nuclear Envelope ) 核被膜 核仁 (Nucleolus) 核仁 核基质 (Nuclear Matrix) 核基质 染色体与染色质 (Chromosome and Chromatin) 染色体与染色质 概要 (Outline)

真核细胞核 Nucleus of a Eukaryotic Cell The cell nucleus is a membrane bound structure Trontana found nucleus of fish cells in Brown found the nucleus of plant cells in The red blood cells of mammalian have no cell nucleus.

An interphase HeLa cell nucleus (Electron micrograph) some components of the nucleus (Diagrammatic view)

lumen Perinuclear space

核被膜 The Nuclear Envelope The separation of a cell’s genetic material from the surrounding cytoplasm most important feature that distinguishes eukaryotes from prokaryotes.

核被膜的结构 Structure of the nuclear envelope 外核膜 (Outer nuclear membrane) 内核膜 (Inner nuclear membrane) 核纤层 (Nuclear lamina) 核周间隙 (Perinuclear space) 核孔复合体 (Nuclear pore complex)

The lamins are 60 to 80 KD fibrous proteins related to the intermediate filament proteins of the cytoskeleton. Function: provide mechanical support to the nuclear envelope.

核被膜的功能 Function of the nuclear envelope  A barrier between the nucleus and cytoplasm as a distinct biochemical compartment  Sole channels by the nuclear pore complexes, which allow the regulated exchange of molecules between the nucleus and cytoplasm.

核孔复合体 Nuclear Pore Complex (NPC) Nuclear pores are found at points of contact between the inner and outer nuclear membranes.  Diameter: 120 nm  molecular mass: 125 million daltons  50  100 proteins  Basketlike apparatus  Eightfold symmetry

核孔的结构 The structure of the NPC 胞质环 (Cytoplasmic ring ): link eightfold symmetry fibers 核质环 (Nuclear ring) 辐 (Spoke): the edge of nuclear pore extend to the central 中央栓 (Central plug): locates the center of nuclear pore

胞质面 Cytoplasmic face 核质面 nucleoplasmic face

核孔的功能 ---- 选择性物质运输 The functions of NPC---- selectively transport  The nuclear proteins are selectively transport across the NPC from the cytoplasm to the nucleus.  Histones, DNA polymerases, RNA polymerases, transcription factors, splicing factors, and many others, transport through NPC by NLS. NLS :nuclear localization signals( 核定位信号 )

The NLS of T antigen and nucleoplasmin a lysine-arginine pair and four lysine T antigen: protein bearing the tumors induced by the SV40 encoded Nucleoplasmin : protein involved in chromatin assembly 7 amino acid sequence

小分子物质以被动运输方式转运 Small molecular traffic through the NPC by passive diffusion Most proteins and RNA pass through the NPC by an active process in only one direction. Small molecules and some proteins with molecular weight less than 50kD pass freely across the NPC in either direction.

Molecular traffic through NPC

核蛋白转运的受体蛋白 Receptors for proteins transport to the nucleus Protein import through the NPC can be divided into two steps The first step does not require energy, NLS of proteins are recognized by a cytosolic receptor, The complex binds to the NPC. The second step is an energy-dependent process that requires GTP hydrolysis.

1. NLS protein binds to receptor (importin αandβ) 2. Protein complex binds to a cytoplasmic filament 3. move through the nuclear pore 4. interacts with Ran-GTP 5. The receptor subunits transported back to cytoplasm dissociate 蛋白核质转运过程 (Importing proteins from the cytoplasm into the nucleus)

RNA 分子的转运 Transport of RNA between nucleus and cytoplasm Active, energy-dependent process Ribonucleoprotein complexes rather than naked RNAs

The transport of RNA molecules through NPC

核仁 (Nucleolus) The nucleolus is the most obvious structure seen in the nucleus of a eukaryotic cell in the light microscope. It is not bound by a membrane.

蛋白质 (protein) 80% RNA 10-11% 、 DNA 8% 少量脂类 (a few lipids) 核仁的化学组成 The chemical components of nucleolus

核仁结构 (Ultra-structure of nucleolus) ❖纤维中心 (Fibrillar centers, FC ) ❖致密纤维组分 (Dense fibrillar component, DFC ) ❖颗粒组分 (Granular component, GC) ❖ 核仁相随染色质 (nucleolar associated chromatin) ❖ 核仁基质 (nucleolar matrix)

核仁功能 Function of the nucleolus The nucleolus is a ribosome production factory ❖ It is the site of rRNA transcription and processing, and of ribosome assembly.

The function of the nucleolus in ribosome synthesis 45S Different transcript unit

Nucleolar cycle

核基质 ( 核骨架 ) Nuclear matrix (skeleton) The protein network in the nucleus Proteinaceous scaffold-like network that permeates the cell. Include components of the chromosomal scaffold that rearranges and condenses to form metaphase chromosomes during mitosis.

Histone-depleted chromosomes consist of a protein scaffold( nonhistone mainly) to which loops of DNA are anchored

SARs/ MARs : scaffold/matrix-associated regions The nuclear matrix, or scaffold, has been defined as the insoluble material left in the nucleus after a series of biochemical extraction steps. Some proteins can be shown to bind specific DNA sequences (AT rich region) called SARs or MARs SARs/MARs

Chromatin is the complex of DNA and proteins found in the interphase cells nucleus of the cell division. Chromosome is the complex of DNA and proteins found in the metaphase of the cell division. 染色质与染色体 Chromatin & Chromosome

Chromatin types ❖常染色质 Euchromatin ❖异染色质 Heterochromatin

常染色质 Euchromatin 存在于间期细胞 (Interphase) 浅染区域 (lightly staining areas) 分布于核中央 (Distribute in the center of the nucleus) 较松散 (More diffuse) 具有转录活性 (Transcriptional activity)

Heterochromatin 存在于间期细胞 (Interphase) 深染区域 (Darkly staining areas) 分布于核周缘 (Distribute around the periphery of the nucleus) 高度浓缩 (Highly condensed) 无转录活性 (Transcriptionally inactive) 分结构性异染色质 (constitutive heterochromatin) 和兼性 异染色质兼性异染色质 ( facultative heterochromatin)

 结构性异染色质 constitutive heterochromatin contains no genes and always be in a compact organization, usually locate in centromere and telomere.  结构性异染色质 facultative heterochromatin contains genes that are inactive in some cells or at some periods of the cell Cycle. X chromosome in female mammals

染色质的功能 The Functions of chromatin Storage of genetic information Precise separation of replicated DNA into two daughter cells Platform for transcription, replication, recombination and DNA repair

染色质的化学组成 Chemical Composition of Chromatin DNA: stable association with histones 组蛋白 (Histones): H1, H2A, H2B, H3, H4, basic protein, rich-arginine and lysine, is main composition of chromosomes. 非组蛋白 (Nonhistone): not as stable as DNA- histone interactions, acidic or neutral protein.

DNA 在染色体上高度浓缩 The DNA in chromosomes is highly condensed DNA are packed into chromosomes in all eukaryotic cells.( for example,each human cell contains 2 m of DNA, yet the cell nucleus is only 5 to 8 um in diameter.

核小体 : 染色质的基本结构单位 Nucleosomes: the lowest level of chromatin organization Nucleosome( 200bp DNA) = a nucleosome core particle + H1 + linker DNA Histone octamer

染色质一级结构 Chromatin structure-primary beads on a string

染色质的二级结构 Chromatin structure-second

染色体的多级折叠 Chromosomes have several levels of DNA packing

中期染色体 Metaphase Chromosomes Highly condensed : morphology can be studied using light microscope.

人类中期染色体 Human metaphase chromosomes 22 对常染色体 (22 pairs of autosomes) 1 对性染色体 (1 pairs of sex chromosome)

中期染色体结构 Metaphase chromosomes structure 异染色质 (heterochromatin) 常染色质 (euchromatin) 着丝点 (Centromere) 染色单体 (chromatid) 次缢痕 (secondary constriction) 短臂 Short arm （ p ） 长臂 Long arm （ q ） 随体 (satellite)

Summary The functions of cell nucleus The structure, function of the nuclear envelope The process of importing proteins from the cytoplasm into the nucleus The characteristics of euchromatin and heterochromatin The structure and function of nucleolus