TOPIC 2: NUCLEUS

Nucleus

The organelle that contains the blueprint for all cell structures and activities encoded in the DNA of chromosomes

Blueprint for all cell structure and Activities

The Nucleus contains ___encoded in the DNA of the chromosomes

Nucleus

Contains the molecular machinery to replicate DNA and synthesize RNA

Nucleus

Controls and regulates cell activities such as growth and metabolism

Hereditary Information

Genetic material stored in the nucleus

Nuclear Envelope

A membrane that separates the nucleus from the cytoplasm

Perinuclear Space

The space between the inner and outer nuclear membranes

Nuclear Envelope Thickness

The nuclear envelope is seven times thicker than the plasma membrane

Outer Nuclear Membrane

Continuous with rough endoplasmic reticulum and contains attached polyribosomes

Inner Nuclear Membrane

Supported by nuclear lamina and attached to chromatin

Nuclear Pores

Openings in the nuclear envelope that allow transport between nucleus and cytoplasm

Nuclear Lamina

A supporting structure beneath the inner nuclear membrane

Beneath the inner nuclear membrane

Nuclear lamina is located ____and it attaches the heterochromatin to the nuclear envelope

Nuclear Lamina Proteins

Composed of intermediate filament proteins called lamins

Lamin Receptors

Proteins that bind chromosomes and secure nuclear lamina attachment

Lamin Receptors, Lamina Associated Proteins

Nuclear lamina contains specific lamin receptors and several lamina associated proteins that bind to chromosomes and secure attachment

Chromatin Attachment

Heterochromatin attaches to nuclear lamina for orderly arrangement

Nuclear Restructure

Nuclear lamina plays a vital role in nuclear reformation

Lamin Mutation

Leads to structural abnormalities of the nucleus

Laminopathies

Genetic diseases caused by impaired nuclear lamina architecture or function

Lamin A/C Mutation

Causes tissue-specific diseases affecting muscle adipose tissue nerves and skeletal development

Premature Aging

Occurs due to abnormal chromatin attachment in lamin defects

Emery-Dreifuss Muscular Dystrophy

A hereditary disease associated with lamin or lamin receptor mutations

EDMD Manifestations

Early tendon contractures muscle weakness muscle wasting and cardiomyopathy

Chromatin

DNA and associated proteins present in the nucleus

Heterochromatin

Electron-dense dark-staining chromatin that is highly condensed and transcriptionally inactive

Euchromatin

Light-staining dispersed chromatin that is transcriptionally active

Barr Body

Dense mass of heterochromatin found in females

Basophilic Clumps

Dark-staining aggregates of heterochromatin due to negative charge

Protein Synthesis Activity

Cells with lightly stained nuclei are more active in protein synthesis

Transcription Availability

Euchromatin provides greater DNA surface for transcription

Condensed Chromatin

Highly coiled DNA less accessible for transcription

Nucleolemma

Region containing chromatin dispersed around the nucleus

Clinical Nuclear Evaluation

Microscopic evaluation of nuclear size shape and structure aids tumor diagnosis

Karyolysis

Disappearance of nuclei due to complete dissolution of DNA by increased DNase activity

Pyknosis

Condensation of chromatin leading to nuclear shrinkage and dense basophilic appearance

Karyorrhexis

Fragmentation of the nucleus during cell death

Nucleosome

The smallest unit of chromatin structure composed of DNA and histones

Nucleosome Core

Octameric complex made of two H2B H3 and H4 histones

DNA Length in Nucleosome

Approximately 150 base pairs wound around the core

Histone H1

Located outside the nucleosome core on the DNA surface

Beads on a String

Description of nucleosomes along DNA

Dynamic Nucleosome

H1 loosens and DNA unwraps frequently to allow transcription factor access

Nucleolus

A spherical structure found in the cell's nucleus whose primary function is to produce and assemble the cell's ribosomes

Nucleolus

A spherical highly basophilic nuclear region active in protein production

Nonmembranous Organelle

A structure not surrounded by a membrane

Ribosomal Production

Primary site of ribosome synthesis and assembly

rRNA Genes

Transcriptionally active genes located in the nucleolus

Initial Ribosomal Assembly

Occurs in the nucleolus before final assembly in cytoplasm

Ribosomal Protein Transfer

Synthesized in cytoplasm and transferred to nucleolus

Multiple Nucleoli

Some cells contain more than one nucleolus

Fibrillar Centers

Contain DNA loops of chromosomes 13 14 15 21 and 22 with rRNA genes

Fibrillar Material

Contains actively transcribed ribosomal genes and rRNA

Granular Material

Contains preribosomal particles for final cytoplasmic assembly

Pars Fibrosa

Region of fibrillar material undergoing transcription

Pars Granulosa

Region of initial ribosomal assembly

Cell Production Balance

Determined by the rate of cell proliferation and cell death

Excess Proliferation Disorders

Hyperplasia cancer and autoimmune diseases

Cell Loss Disorders

Atrophy degenerative diseases AIDS and ischemic injury

AIDS Mechanism

Decrease in CD4 T cells attacked by the virus

Opportunistic Infection

Occurs due to impaired immune system such as Candida albicans infection

Excess Cell Loss Examples

AIDS Alzheimer’s disease Parkinson’s disease aplastic anemia and myocardial infarction

Cell Accumulation Disorders

Cancer lupus erythematosus glomerulonephritis and viral infection

Necrosis

Pathologic accidental cell death caused by acute injury

Necrosis Cause

Unfavorable physical or chemical environment damaging plasma membrane

Perforins

Proteins that initiate plasma membrane damage

Necrosis Features

Rapid cell swelling and lysis

Necrosis DNA Pattern

Bursting and random fragmentation

Necrosis Cytoplasm

Swelling and inflammation

Necrosis Membrane

Breakdown and leakage

Necrosis Outcome

Inflammation and damage to surrounding cells

Apoptosis

Programmed cell death without damage to neighboring cells

Autodigestion

Controlled self-digestion of dying cell

Dignified Cell Death

No spilling of contents and no damage to neighbors

Apoptotic Blebbing

Formation of membrane blebs and apoptotic bodies

Membrane Blebbing

Alteration of cell membrane forming protrusions

Apoptotic Bodies

Final fragmented membrane-bound cell portions

DNA Fragmentation

Irreversible commitment to apoptosis

Endonuclease Activation

Ca2 and Mg2 dependent enzymes fragment DNA

Cell Shrinkage

Decrease in cytoplasmic volume during apoptosis

Ribosome Clumping

Aggregation of ribosomes within cytoplasm

rER Whorls

Concentric formations of rough endoplasmic reticulum

Mitochondrial Permeability Change

Loss of mitochondrial function during apoptosis

Apoptosis DNA Pattern

Controlled fragmentation

Apoptosis Cytoplasm

Shrinkage and restructuring

Apoptosis Membrane

Intact with bleb formation

Apoptosis Outcome

No inflammation and no damage to neighboring cells