nucleus - webs · the nuclear envelope (also known as the perinuclearenvelope, nuclear membrane,...

2005-2006

� Nucleus = L. nux = Nut ; Greek – Karyon

� Discovered and named by Robert Brown 1833

� Nucleolus = coined by Bowman 1840

� Chromatin = W. Flemming 1879

� Nucleoplasm = Strasburger 1882

� Shape and size varies

� Nuclear Envelope

� Nucleoplasm

� Chromatin

� Nucleolus

� Function

� contains eukaryotic cell’s genetic library ▪ most genes in nucleus

▪ some genes located in mitochondria & chloroplasts

� Size

� ~ 5 microns (µm) in diameter

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� Structure

� separated from cytoplasm by a double membrane, nuclear envelope

� double membrane is fused in spots forming pores

� allows large macromolecules & particles to pass through

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What kind of molecules

need to pass through?

� Within nucleus, DNA organized into fibrous material, chromatin� in normal cell appears as diffuse mass

� When cell prepares to divide, chromatin fibers coil up as separate structures, chromosomes

� Densely stained region = nucleolus

� Function

� production of ribosomal subunits from rRNA & proteins

▪ pass through nuclear pores to cytoplasm & combine to form ribosomes

Animation

2005-2006

� The entire nuclear pore complex (NPC) has a

diameter of about 120 nm

� The diameter of the opening (functional diameter) is

about 9 nm wide and its "depth" is about 200 nm

� It had been suggested that the pore can be dilated to

around 26 nanometers to allow molecule passage.

� The molecular mass of the mammalian NPC is about

120 megadaltons

� It contains approximately 30 different protein

components, each in multiple copies

Nuclear envelope

Outer ring

Spokes

Basket

Filaments

Proposed str

� The nuclear envelope (also known as the perinuclear envelope, nuclear membrane, nucleolemma or karyotheca)

� a double lipid bilayer that encloses the genetic material in eukaryotic cells.

� Serves as the physical barrier, separating the

contents of the nucleus (DNA in particular)

from the cytosol (cytoplasm).

� Many nuclear pores are inserted in the nuclear envelope, which facilitate and regulate the exchange of materials

� Prominent, spherical, colloidal acidophilic bodies in the

nucleus.

� Bacterial and yeast cells lacks

� Size related with synthetic activities of the cell

� Number depends upon species and the no. of chromosomes

� Associated with Nucleolar Organizer (NO) region (Secondary

Constriction)

� – 10 in Human

� NO consist of genes for 18, 5.8, & 28 S rRNA and 5 S rRNA

outside the NO

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� The nucleolus (nucleole)

� It is a non-membrane bound structure

�Composed of

�proteins

�nucleic acids (rRNA)

� Function

� protein production� Structure

� ribosomes contain rRNA & protein

� composed of 2 subunits that combine to carry out protein synthesis

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� Free ribosomes

� suspended in cytosol

� synthesize proteins that function within cytosol

� Bound ribosomes

� attached to outside of endoplasmic reticulum

� synthesize proteins for export or for membranes

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� Prokaryotes & eukaryotes have different ribosomes

� different size subunits

� different proteins

� can this difference be useful?

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