3. THE NUCLEUS

nucleus

contains a blueprint for all cell structures and activities encoded in the DNA of the chromosomes.

nucleus

contains the molecular machinery to replicate its DNA and to synthesize an RNA

– Nuclear envelope

– chromatin

– nucleolus

Components of the nucleus:

perinuclear space

the space between the inner and outer nuclear membrane

karyolysis

___________ , or the disappearance of nuclei due to complete dissolution of DNA by increased activity of DNAase

pyknosis

__________ , or condensation of chromatin leading to shrinkage of the nuclei (they appears as dense basophilic masses)

karyorrhexis

___________ , or fragmentations of nuclei

Nuclear Envelope

Selectively permeable membrane that is seven times thicker than plasma membrane and perforated by nuclear pores

outer nuclear membrane

Continuous with the rough ER membrane and has attached polyribosomes.

inner nuclear membrane

Supported by a rigid network of intermediate filaments on its inner surface called the nuclear (fibrous) lamina.

nuclear (fibrous) lamina

is a protein filament attached to the inner nuclear membrane that supports the nuclear envelope and the site where chromatins attaches

nuclear pore

in areas where inner and outer nuclear membrane meets, ___________ forms

laminopathies

Genetic diseases caused by impairment in nuclear lamina structure or function, associated with mutations of lamin A/C and with apoptosis.

Emery–Dreifuss muscular dystrophy (EDMD)

Hereditary muscular dystrophy associated with mutations in lamins or lamin receptors.

Chromatin

In non-dividing cells, consists of DNA and associated proteins in a largely uncoiled state.

Heterochromatin

Densely packed chromatin; appears as coarse electron-dense material on EM and basophilic clumps on LM; includes Barr bodies in females.

Barr bodies

Dense mass of heterochromatin representing the inactive X chromosome in females.

Heterochromatin

a type of chromatin that is predominant in metabolically inactive cell (ie. lymphocytes, sperm cells, plasma cells)

euchromatin

a type of chromatin that is predominant in metabolically active cells (i.e. neurons, liver cells). thus it is spread/streched out to be read and translate.

euchromatin ; heterochromatin

lightly stained ; ______________

dark-stained ; _______________

nucleosome

The smallest units of chromatin structure are macromolecular complexes of DNA and histones called ___________

chromosomes

In dividing cells, chromatin is condensed and organized into discrete bodies called _____________

centromere

The point of attachment where two chromatids are joined.

Telomere

Region at each end of a chromosome that protects chromosomal DNA.

telomerase

Enzyme that adds repeated nucleotide sequences to telomere ends, maintaining telomere length and extending cell lifespan; active in malignant (immortalized) cells.

autosomes

22 pairs of chromosomes that are identical and contain the same portions of the genome.

sex chromosomes

The 23rd pair of chromosomes that determines biological sex.

Nucleolus

is a spherical, highly basophilic sub domain of nuclei in cells, actively making proteins

Nucleolus

It is a nonmembranous region of the nucleus that surrounds transcriptionally active rRNA genes.

Nucleolus

It is the primary site of ribosomal production and assembly

1. Fibrillar centers

2. Fibrillar material (pars fibrosa)

3. Granular material (pars granulosa)

enumerate the three distinct regions of the nucleolus:

Fibrillar centers

contain DNA loops of five different chromosomes (13, 14, 15, 21, and 22) that contain rRNA genes, RNA polymerase I, and transcription factors

Fibrillar material (pars fibrosa)

Region where ribosomal genes are actively transcribed and contains large amounts of rRNA

Granular material (pars granulosa)

Site of initial ribosome assembly containing densely packed preribosomal particles.

1. Necrosis

2. Apoptosis

Two Major Mechanisms of Cell Death

Necrosis

or accidental cell death, is a pathologic process

Necrosis

• It occurs when cells are exposed to an unfavorable physical or chemical environment that causes acute cellular injury and damage to the plasma membrane.

• Damage to the plasma membrane may also be initiated by viruses, or proteins called perforins.

• Characteristic feature: Rapid cell swelling and lysis

Apoptosis

[Gr., falling off, as petals from flowers] was referred to in the past as programmed cell death

Apoptosis

• It is characterized autodigestion by controlled

• The cell “dies with dignity” without spilling its contents and damaging its neighbors

DNA fragmentation

– an irreversible event that commits the cell to die.

– a result of Ca2-dependent and Mg2-dependent activation of nuclear endonucleases