北京大学：《分子细胞生物学》课程教学资源（PPT课件讲稿，英文版）Chapter 8 Nucleus and chromosomes

Chapter 8 Nucleus and chromosomes Learning Objectives (1)A typical nonmitotic nucleus includes several major components. (2) Nuclear envelope and nuclear pore complex. (3)The components of chromatin and packaging of chromosome (4) Nucleolus

Nucleus and Chromosomes Chapter 8 Learning Objectives (1) A typical nonmitotic nucleus includes several major components. (2) Nuclear envelope and nuclear pore complex. (3) The components of chromatin and packaging of chromosome. (4) Nucleolus

1. The nucleus: Nuclear envelope and npc A. Structure: Double-membrane nuclear envelope surrounds the nucleus Nuclear lamina lucien enve nner nuclear Nucleolus embrane Chromatin Perinuclear space SeNUCLEOPLAS Figure 16-26 The Structural Organization of the Nucleus and Nuclear pores Nuclear Envelope. (a) An electron micrograph of the nucleus frum a mouse liver cell, with prominent structutal features labeled(TEM The CYTOSOL nuclear envelope is a doutle membrane perforated ty iclear pores INP) Internal structures include the nucleolus nu), euchromatin (eu), and heterochromatin (he).(b)A drawing of a typical nucleus Structural Rough ER features included here but not visible in he micrograph include the nuclear lamina niosomes on the outer nuclear membrane. and the continuity between the outer nuclear membrane and the rough ER

1. The nucleus: Nuclear envelope and NPC A. Structure: Double-membrane nuclear envelope surrounds the nucleus

B. The nuclear envelope consists consists of two membranes by a perinuclear space. The inner surface of the nuclear envelope is lined by the nuclear lamina > The nuclear lamina supports the nuclear envelope: Gives shape and stability of nuclear envelope: Provides a structure link between chromatin and nuclear envelope > The nuclear lamina is composed of lamins >The integrity of the nuclear lamina is regulated by phosphorylation and dephosphorylation

B. The nuclear envelope consists consists of two membranes by a perinuclear space. ❖The inner surface of the nuclear envelope is lined by the nuclear lamina ➢The nuclear lamina supports the nuclear envelope: Gives shape and stability of nuclear envelope; Provides a structure link between chromatin and nuclear envelope ➢The nuclear lamina is composed of lamins. ➢The integrity of the nuclear lamina is regulated by phosphorylation and dephosphorylation

nucloar pore lamins DNA inner nuclear membrane nuclear envelope outer nuclear membrane nuclear pore PHOSPHORYLA complex proteins FUSION OF ENVELOPED CHROMOSOMES phosphorylated INTERPHASE NUCLEUS P chromatid nuclear envelope somOsomo fragment LATE TELOPHASE PROPHASE DEPHOSPHORYLATION FUSION OF NUCLEAR OF LAMINS ENVELOPE FRAGMENTS EARLY TELOPHASE Breakdown and reformation of nuclear envelope during mitosis

Breakdown and reformation of nuclear envelope during mitosis

>The phosphorylation of the lamins triggers the disassembly of the nuclear lamina, which in turn cause the nuclear envelope to break up into vesicles phosphorylation of the lamins helps reverse the process. >Because the new nuclear envelope is so closely applied to the surface of the chromosomes. it excludes all of the proteins in the cell except those bound to the chromosomes. So nuclear localization signals are not cleaved off after transport into the nucleus Old nuclear envelope reforms new nuclear envelope

➢The phosphorylation of the lamins triggers the disassembly of the nuclear lamina, which in turn cause the nuclear envelope to break up into vesicles. Dephosphorylation of the lamins helps reverse the process. ➢Because the new nuclear envelope is so closely applied to the surface of the chromosomes, it excludes all of the proteins in the cell except those bound to the chromosomes. So nuclear localization signals are not cleaved off after transport into the nucleus. ➢Old nuclear envelope reforms new nuclear envelope

C Nuclear pore complex (NPC) NUCLEOPLASM Inner membrane Nuclear of nuclear envelope pore complex 120nm一 Basket of fibers Anchor Nuclear protein lamina Ri Nuclear Ring Cytoplasmic Ring membrane Transporter of nuclear envelope Fibe EndoplasmIc reticulum Ribosomes CYTOSOL

C. Nuclear pore complex (NPC) Cytoplasmic Ring Nuclear Ring

D. Molecules enter and exit the nucleus through nuclear pore complex RN Chromosomal replication DNA mRNA tRNA Ribosomal NUCLEUS Proteins needed Proteins needed for chromosome prote Protein syn wing CYTOPLASM Completed protein Bidirectional traffic

D. Molecules enter and exit the nucleus through nuclear pore complex Bidirectional traffic

o Passive transport--passively diffuse >3000-4000 NPC/cell (mammalian); To import about 106 histone/3 mins. (DNA-Sythesizing cell)=100 histone/ min/NPC >Each NPC contains one or more open aqueous channels:9 nm in diameter and 15 nm long The effective size of these channels has been determined by injecting various sizes of colloidal gold particles and examined by electron microscopy. <10 nm in diameter able to enter the nucleus <60kd globular protein

❖ Passive transport—passively diffuse ➢3000-4000 NPC/cell(mammalian); To import about 106 histone/3 mins.(DNA-sythesizing cell) = 100 histone/ min/NPC ➢Each NPC contains one or more open aqueous channels: 9 nm in diameter and 15 nm long ➢The effective size of these channels has been determined by injecting various sizes of colloidal gold particles and examined by electron microscopy. <10 nm in diameter <60kd globular protein Able to enter the nucleus

☆ Active transport limited proteolysis radioactive radioactive radioactive colloidal gold particle nucleoplasmin coated with tails MICROINJECTION INTO CYTOSOL OF XENOPUS OOCYTE 0)(a(8 nucleus. INCUBATION DETECTION BY AUTORADIOGRAPHY DETECTION BY EM UPTAKE INTO UPTAKE INTO NUCLEUS UPTAKE NOCLEUS UPTAKE INTO NUCLEUS > Transport of large proteins into nucleus needs nuclear localization signal (NLs)

❖ Active transport ➢Transport of large proteins into nucleus needs nuclear localization signal (NLS)

NLS are present only in nuclear proteins A typical NLs contains several consecutive basic amino acids (the positively charged Aa: Lys, Arg) Normal pyruvate kinase: Chimeric pyruvate kinase in cytosol containing sv40 Nls: in nucleus

➢ NLS are present only in nuclear proteins A typical NLS contains several consecutive basic amino acids (the positively charged Aa: Lys, Arg) Normal pyruvate kinase: in cytosol Chimeric pyruvate kinase containing SV40 NLS: in nucleus