ultra structure of nucleus
Transcript of ultra structure of nucleus
Ultra structure of Nucleus sana khan
“Nucleus” is a Latin word meaning Kernel
It is the “CONTROL CENTER” of the cell
It was First cell organelle to be discovered
It is membrane bound organelle found in
eukaryotic cells
Main functions are
- to maintain the integrity of genes
- to control the activities of the cell by regulating
gene expression .
Intorductions
Average diameter of nucleus is 6um, which
occupies around 10% of cell volume
Nuclear Envelope
Nuclear Pores and complex
Nuclear lamina
Chromosomes & Chromatin
Nucleolus
Nucleoplasm
Structure
Also known as perinuclear envelope, nuclear
membrane or karyotheca
Encloses the nucleus and separates the cell's
genetic material from the surrounding cytoplasm
It is a lipid bilayer
Consists two cellular membranes, an inner &
outer membrane, arranged parallel to one another
and separated by 10-50(nm) of space.
The membranes of the nuclear envelope serve as
a barrier that keeps ions, solutes ,and macro-
molecules from passing freely between the
nucleus and cytoplasm.
Nuclear envelope
0uter 0uter MembraneMembrane
6 nm thick
Faces cytoplasm and is continuous at certain sites
with the RER
A loosely arranged mesh of intermediate filaments
(vimentin)
Ribosome stud the cytoplasmic surface of the outer
nuclear membrane
Ribosome synthesize proteins that enter the
perinuclear cisterna (space between two membranes
10-50nm wide)
Faces the nuclear material
Primary site for location of inner nuclear
membrane proteins IMP
Inner membrane proteins – used during formation
of nuclear envelope during mitosis as well as some
role in transcriptional activity.
Outer and inner membranes are fused at the
nuclear pore complex sites
Inner Membrane is supported underneath by
Nuclear lamina.
Inner membraneInner membrane
Network of intermediate filaments, The filament of
the nuclear lamina are approximately 10 nm in
diameter and composed of polypeptides, called
lamins. Composed primarily of lamins A, B1, B2 and
C
Helps in organizing the nuclear envelope and
perinuclear chromatin ,Also plays a role in DNA
elongation phase
Essential during mitotic events where,
Phosphorylation of lamins leads to disassembly, and
dephosphorylation results in reassembly of the
nuclear envelope.
Apoptosis a highly regulated process in which
nuclear lamina is disassembled following proteolytic
activity of caspase protein.
Nuclear laminaNuclear lamina
Nuclear pores are aqueous channels through the
nuclear envelope
Composed of multiple proteins called “nucleoporins.”
Have molecular weight of 125 KD
Nucleus of a cell has 3000 - 4000 pores
Pores are formed by fusion of outer and inner nuclear
membranes
Nuclear Apore complex permits passive movement
across the nuclear envelope via 9-11nm channels
by simple diffusion
Nuclear pores and complex
Allows free passage of water soluble molecules
Most proteins, ribosomal subunits and RNA are
transported via transport factors called
KARYOPHERINS
a) Importins –that mediate movement into the
nucleus
b) Exportins –that mediate movement out of nucleus
Nuclear pore complex is composed of nearly 100
proteins, arranged in eight-fold symmetry around the
margin of the pore.
NUCLEAR PORE
STRUCTURE
Cytoplasmic ring
Nucleoplasmic ring
Middle ring.
Nucleoplasmic side-
Nuclear basket
Cytoplasmic side -
displays fibers
Nucleoplasm is the protoplasm within the nuclear
envelope. Nucleus is filled with a semi-solid granular slightly
acidic ground matrix called as nucleoplasm. The chromatin fibres and nucleolus remain
suspended in the nucleoplasm. Major component of nucleoplasm are
nucleoproteins. Both nucleic acids, RNA and DNA
are present in the nucleoplasm that may occur
either as polymers or monomeric nucleotides. Basic proteins like nucleoprotamines, histones and
acidic proteins (non-histone proteins).
NucleoplasmNucleoplasm
► Chromatin are coiled elongated thread like fibres
visible during the interphase and can readily take
up basic stains like basic fuschin.► During cell division where these chromatin fibres
get thickened to form a ribbon like structure called
“chromosomes”.► chromatin is a nucleoprotein complex composed of
DNA and proteins and very small quantity of RNA.► Chromatin are of 2 types:
Heterochromatin and euchromatin.
Chromatin & Chromatin & chromosomechromosome
Heterochromatin: The deeply stained and highly
condensed region of the chromatin that occurs
around the nucleolus or at the periphery of the
nucleus.
heterochromatin is transcriptionally inactive and
metabolically inert.
Euchromatin is the lightly stained and diffused region
of the chromatin that is transcriptionally active.
Metaphase chromatin- the chromatin becomes
more and more condensed and compact, making
the chromosome visible with a classic four arm
structure, having a pair of sister chromatids
attached at centromere. Humans have 23 pairs of chromosomes- 22 are
autosomes & 2 sex chromosomes.
Nucleolus is the discrete densely stained
structure found in nucleus
It is a nuclear inclusion that is not surrounded
by a membrane
Present in cells that are actively synthesizing
proteins
Its size depends on metabolic activity of cell
Average size -5.5µm in diameter.
It is generally detectable when the cell is in
interphase
Synthesis of rRNA and its assembly into
ribosome precursors- main function
More than one nucleolus can be present in the
nucleus
Nucleolus
Conclusively cell nucleus is the storehouse of Conclusively cell nucleus is the storehouse of everything what a cell shall do in future, since it everything what a cell shall do in future, since it
handles the gene expression and overall handles the gene expression and overall metabolism of cellmetabolism of cell
thus calledthus called “DIRECTOR OF CELL”“DIRECTOR OF CELL”
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