southeast university genetic center

第六节 细胞核第六节 细胞核 Cell NucleusCell Nucleus

细胞核的功能细胞核的功能The functions of cell nucleusThe 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 )

核被膜(Nuclear Envelope )

核仁(Nucleolus)

核基质(Nuclear Matrix)

染色体与染色质(Chromosome and Chromatin)

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 1781.Brown found the nucleus of plant cells in 1831.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

核被膜核被膜The Nuclear EnvelopeThe Nuclear Envelope

The separation of a cell’s genetic material

from the surrounding cytoplasm

most important feature that distinguishes

eukaryotes from prokaryotes.

核被膜的结构核被膜的结构Structure of the nuclear envelopeStructure 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.

核被膜的功能核被膜的功能Function of the nuclear envelopeFunction 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.

核孔复合体核孔复合体Nuclear Pore Complex (NPC)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 50100 proteins Basketlike apparatus Eightfold symmetry

核孔的结构核孔的结构The structure of the NPCThe structure of the NPC

胞质环 (Cytoplasmic ring ): link eightfold symmetry fibers

核质环 (Nuclear ring)辐 (Spoke): the edge o

f 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

核孔的功能核孔的功能 -------- 选择性物质运输选择性物质运输The functions of NPC---- selectively transThe functions of NPC---- selectively trans

portport

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 nucleoplasminThe NLS of T antigen and nucleoplasmin

a lysine-arginine pair and four lysine

T antigen: protein bearing the tumors induced by the SV40 encodedNucleoplasmin : protein involved in chromatin assembly

7 amino acid sequence

小分子物质以被动运输方式转运小分子物质以被动运输方式转运Small molecular traffic through the NPC Small molecular traffic through the NPC

by passive diffusionby 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 NPCMolecular traffic through NPC

核蛋白转运的受体蛋白核蛋白转运的受体蛋白Receptors for proteins transport to thReceptors for proteins transport to th

e nucleuse 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 filament3. move through the nuclear pore 4. interacts with Ran-GTP5. The receptor subunits transported back to cytoplasm

dissociate

蛋白核质转运过程 (Importing proteins from the cytoplasm into the nucleus)

RNARNA 分子的转运分子的转运Transport of RNA between nucleus and cTransport of RNA between nucleus and c

ytoplasmytoplasm

Active, energy-dependent process

Ribonucleoprotein complexes rathe

r than naked RNAs

The transport of RNA molecules through NPC

核仁 核仁 (Nucleolus)(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 核仁结构 (Ultra-structure of nucleolus)(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)

核仁功能核仁功能Function of the nucleolusFunction 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

45SDifferent transcript unit

Nucleolar cycle

核基质核基质 (( 核骨架核骨架 ))Nuclear matrix (skeleton)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.

染色质与染色体染色质与染色体Chromatin & ChromosomeChromatin & Chromosome

Chromatin types

❖ 常染色质 Euc

hromatin

❖ 异染色质 Heteroc

hromatin

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)

HeterochromatinHeterochromatin存在于间期细胞 (Interphase)深染区域 (Darkly staining areas)分布于核周缘 (Distribute around the p

eriphery 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 heterochromatincontains no genes and always be in a compact organization, usually locate in centromere and telomere. 结构性异染色质 facultative heterochromatincontains genes that are inactive in some cells or a

t some periods of the cell Cycle.

X chromosome in female mammals

染色质的功能染色质的功能The Functions of chromatinThe Functions of chromatin

Storage of genetic information

Precise separation of replicated DNA into two

daughter cells

Platform for transcription, replication,

recombination and DNA repair

染色质的化学组成染色质的化学组成Chemical Composition of ChromatChemical Composition of Chromat

inin

DNA: stable association with histones组蛋白 (Histones): H1, H2A, H2B, H3, H4 , basi

c 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.

DNADNA 在染色体上高度浓缩在染色体上高度浓缩The DNA in chromosomes is highly condensedThe 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.

核小体核小体 :: 染色质的基本结构单位染色质的基本结构单位Nucleosomes: the lowest level of chromatiNucleosomes: the lowest level of chromati

n organizationn organization Nucleosome( 200bp DNA) = a nucleosome core

particle + H1 + linker DNA

Histone octamer

染色质一级结构染色质一级结构Chromatin structure-primaryChromatin structure-primary

beads on a string

染色质的二级结构染色质的二级结构Chromatin structure-secondChromatin structure-second

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

中期染色体中期染色体Metaphase ChromosomesMetaphase Chromosomes

Highly condensed : morphology can be studied using light microscope.

人类中期染色体人类中期染色体Human metaphase chromosomesHuman metaphase chromosomes

22 对常染色体(22 pairs of autosomes)

1 对性染色体 (1 pairs of sex chromosome)

中期染色体结构中期染色体结构 Metaphase chromosomes structureMetaphase 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)

SummarySummary

The functions of cell nucleusThe structure , function of the nuclear envelo

peThe process of importing proteins from the cy

toplasm into the nucleusThe characteristics of euchromatin and hetero

chromatinThe structure and function of nucleolus