Cell Nucleus. Chen Li. Department of Cellular and Genetic Medicine

Transcription

1 Cell Nucleus Chen Li Department of Cellular and Genetic Medicine

2 Outline A. Historical background B. Structure of the nucleus: nuclear pore complex (NPC), lamina, nucleolus, chromatin C. Function of the nucleus: passive diffusion and active transport through the NPC, breakdown and re-formation of nuclear lamina, chromatin assembly, chromatin modifications

3 A. Historical background

4 Discovery of the nucleus Robert Hooke (British), 1665 Antonie van Leeuwenhoek (Dutch), 1674 Robert Brown (Scottish),1831

5 Characteristics of the nucleus Largest cellular organelle in animals Mammalian red blood cells do not have nucleus Appear in interphase, disappear in mitosis

6 Size of nuclei in different cells Type Animal cell nucleus Plant cell nucleus Eukaryote cell Prokaryote cell (no nucleus) Diameter 5-10 μm 5-20 μm μm 5-10 μm

7 B. Structure of the nucleus C. Function of the nucleus

8 Structure of the nucleus

9 Detailed structure of the nucleus Nuclear envelope inner nuclear membrane outer nuclear membrane Perinuclear space Nuclear pore complex (NPC) Lamina (envelope) nucleus Nuclear skeleton nuclear matrix chromosome scaffold fibrillar component nucleolus Granular component chromatin Perinucleolar heterochromatin euchromatin

10 Structure of the nuclear envelope

11 Function of the nuclear envelope Separate DNA, RNA and protein Transport RNA, RNP, nuclear protein through nuclear pore

12 The nuclear pore complex (NPC)

13 Structure of the NPC (top view) Octagon structure Ring, spoke, plug Wheel with 8 spokes

14 Structure of the NPC (side view) Nuclear ring, cytoplasmic ring Sandwich, basket

15 Function of the NPC Provide aqueous channels Allow small molecules freely permeable Block large molecules transported selectively. Bidirectional transportation Transport RNA, RNP, nuclear protein through nuclear pores.

16 Passive diffusion through the NPC Allows free entry/exit of many small molecule (< 10 nm) and proteins (< 60 kd) Exceptions: some small molecules are actively transported or blocked

17 Active transport through the NPC Regulates the entry/exit of molecules based on the recognition of nuclear localization sequence (NLS) or nuclear export signal (NES) Requires energy: RAN cycle (Ras-related nuclear protein) [Ran-GTP Ran-GDP] nuclear import receptor (importin), export receptor(exportin)

18 Nuclear localization sequence (NLS) nuclear resident protein, NLS-protein basic amino acid No conservation in sequence NLS not be cut after transport. PKKKRKV SV40 Exception

19 Receptor-mediated entry/exit Nuclear import receptor: importin export receptor: exportin Energy source: Ras-related nuclear protein (RAN) cycle [Ran-GTP Ran-GDP]

20 NLS-protein import (binding)

21 NLS-protein import (translocation)

22 NES-protein export

23 Nuclear lamina

24 Structure of nuclear lamina

25 Function of Nuclear lamina Provides stability Anchors the NPC Binds the inner nuclear membrane Transduces signals Anchors perinuclear chromatin

26 Function of Nuclear lamina Lamina breakdown take place in interphase prophase Lamin phosphorylated by lamin kinase p34/cdc2 Lamin A/C depolymerized Nuclear membrane breakdown into vesicles attach with Lamin B

27 Breakdown and re-formation of nuclear lamina

28 No membrane organelle Fibrillar & granular components NORs rrna + Ribonucleoprotein (RNP) = ribosome Nucleolus

29 Chromatin Chromatin contains DNA and proteins. Histone /nonhistone proteins

30 DNA: deoxyribonucleic acid Watson & Crick, 1953

31 Histones DNA is bound to the histones through electrostatic forces between the negatively charged phosphate groups in the DNA backbone and positively charged amino acids. Found only in eukaryotic cells

32 Non-histone proteins Sequence specific DNA binding proteins (e.g., transcription factors) Enzymes (DNA polymerase, RNA polymerase), structural proteins (e.g., high mobility group protein: HMG), additional regulatory proteins

33 Chromatin structure Nucleosome, H1, H2A, H2B, H3, and H4 and DNA. Octamer (H3) 2 (H4) 2 (H2A H2B) 2, 146 bp DNA, 1.75 round H1, 20 bp DNA Linker DNA, 60bp, beads-on-astring

34 Chromatin assembly 2 m dsdna in nucleus of 10 μm diameter = 2 Km thread in a tennis ball! Condenses about 10,000-fold during cell division

35 Chromatin assembly Step 1: 2 nm dsdna 10 nm nucleosome (7-fold) Step 2: 10 nm nucleosome 30 nm solenoid (6-fold)

36 Chromatin assembly

37 Chromatin assembly Step 3: 30 nm solenoid 300 nm supersolenoid (10 fold) Scaffold-radial loop structure model Step 4: 300 nm super-solenoid 700 nm chromatin fiber miniband (4 fold) Miniband Step 5: 700 nm chromatin fiber 1.4 μm chromatid (5 fold)

38 Chromatin assembly

39 Multiple coiling model From DNA to chromosome

40 Euchromatin & Heterchromatin Type Euchromatin Heterchromatin Phase interphase interphase Form Extend form Condense form Fold <2000 fold condensation >2000 fold condensation Condensation solenoid super-solenoid,chromatin fiber Dye Basic dye light Basic dye dark Activity Transcriptionallyactive transcriptionallyinactive Subtype H1 less more Histone acetylation high low Constitutive & facultative

41 Clinical implications Barr bodies One of the female X chromosome is randomly inactive. Chimera Fragile X syndrome

42 Chromatin modifications DNA methylation Histone acetylation Phosphorylation

43 Chromatin modifications DNase I hypersensitive sites Chromatin accessibility

44 ENCODE Encyclopedia of DNA Elements (ENCODE) Consortium research progress: Nature 9/2012 A landmark in the understanding of the human genome after Human Genome Project. Catalogs regulatory events that act at DNA, RNA, and protein levels

45 Chromosomes during cell division Appear in metaphase Sister chromatids

46 Human chromosome karyotype

47 Chromosome structure 3 functional elements: origin, Centromere (primary constriction), Telomere Four types: Metacentric, Submetacentric, Acrocentric, Telocentric chromosome

48 Chromosome structure bp, ~21,000 protein coding genes Non-repetitive DNA: protein coding sequences Moderately Repetitive DNA: SINEs, LINEs, regulatory sequences, rrna, trna, histone Highly Repetitive DNA: satellite DNA, mini-satellite DNA, micro-satellite DNA

49 Functions of the nucleus Houses chromosomes Provides an isolated environment for DNA replication and gene expression Provides an isolated environment for the processing of mrna and rrna Regulates the entrance and exit of proteins and nucleic acids from/to the cytoplasm How cell nucleus functions

50 Thanks!