ch12im - The Nucleus of a Eukaryotic Cell: An Overview

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
The Nucleus of a Eukaryotic Cell: An Overview I. Cells possess mechanisms that allow them to express their genetic information selectively, following only those instructions that are relevant for that cell at that particular time II. Nuclear contents - viscous, amorphous mass of material enclosed by a complex nuclear envelope that forms a boundary between the nucleus & cytoplasm; its morphology is relatively undistinguished III. Included within a typical interphase (nonmitotic) cell nucleus are: A. Chromosomes – present as highly extended nucleoprotein fibers called chromatin B. Nuclear matrix - protein-containing fibrillar network C. Nucleolus (nucleoli - plural ) - one or more; irregularly-shaped, electron-dense, amorphous structures that D. Nucleoplasm - the fluid substance in which the solutes of the nucleus are dissolved The Nuclear Envelope I. The nuclear envelope is complex; consists of several distinct components; core of nuclear envelope consists A. Separates genetic material in nucleus from cytoplasm - important distinction (maybe the single, most important one) between prokaryotes & eukaryotes; its appearance is an evolutionary landmark 1. B. Fused at sites forming circular pores that contain complex assemblies of proteins 1. Average mammalian cell: contains ~3000 nuclear pores 2. Pore density: ~2-4/μm 2 (metabolically inactive bird erythrocyte) to >60/μm 2 (active oocyte) C. Outer membrane is generally studded with ribosomes & is often seen to be continuous with RER membrane; the space between the membranes is continuous with the ER lumen D. Inner surface of the nuclear envelope of animal cells is bound by integral membrane proteins to a thin filamentous meshwork ( nuclear lamina ) 1. Provides mechanical support to nuclear envelope, serves as a site of attachment for chromatin fibers at 2. Filaments of nuclear lamina are ~10 nm in diameter, made of polypeptides called lamins (members of the same superfamily of polypeptides that assemble into the 10-nm intermediate filaments) 3. As in cytoplasm, the integrity of the intermediate filaments that make up the nuclear lamina is 4. Nuclear lamina disassembly prior to mitosis is thought to be induced by phosphorylation of the lamins by a specific protein kinase E. Mutations in one of lamin genes ( LMNA ) are responsible for several distinct human diseases, including rare form of muscular dystrophy (EDMD2) in which muscle cells contain exceptionally fragile nuclei 1. Lamin A mutations are also linked to a disease (Hutchinson-Gilford progeria syndrome (HGPS) that is
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/10/2008 for the course BIO 201 taught by Professor Janicke during the Spring '08 term at SUNY Buffalo.

Page1 / 36

ch12im - The Nucleus of a Eukaryotic Cell: An Overview

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online