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� 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
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� Nuclear Envelope
� Nucleoplasm
� Chromatin
� Nucleolus
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� 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?
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� 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
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� Densely stained region = nucleolus
� Function
� production of ribosomal subunits from rRNA & proteins
▪ pass through nuclear pores to cytoplasm & combine to form ribosomes
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Animation
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� 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
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Nuclear envelope
Outer ring
Spokes
Basket
Filaments
Proposed str
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� 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
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� 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)
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� 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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