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INTRODUCTIONNucleus is a prominent organelle in the cell .
Eukaryotic cell (well distinguished morphology) and prokaryotic cell (nucleoid) .
Nucleus is control the activity of cell .
Largest organelle in the cell .
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HISTORY
Nucleus ( latin ) is discovered by ROBERT BROWN scottish botinsist in 1831 .
He told it plays key role for fertilization and embryo development .
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POSITION OF NUCLEUS Nucleus is present in center , eccentric postion
because of cell secritions accumulate inside the cell .
SHAPE , SIZE . It is round , oval , spherical ,
ellipsoidal or disc shaped .
Depending on the cell size of nucleus is variable and it directly proportional to cytoplasm .
Using HEYWIG’S formula
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No of nucleus defination exampleMononucleate The cell contains
single nuclei Amoeba
Binucleate The cell which contains two nuclei _ 1 . micronucleus2 . macronucleus
Paramecium
Polynucleate The cell which contain more than two nuclei .
Animal (syncytial)
Plant (coenocyte)
Epidermal cell of ascaris .
Osteoblast .
Vaucheria .
NUMBER
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ULTRA STRUCTURE OF NUCLEUS Typical structure of nucleus
showing these components .
Nuclear envelope
Nuclear sap
Chromatin
Nucleolus
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NUCLEAR ENVELOPE (KARYOTHECA)
This envelope is distinguish nucleus responsible for communication between cytoplasm and nucleus the phospholipid bilayer .
1 )outer membrane 2 )Inner membrane . In between the membrane
perinuclear space (10 to 50 nm) is present .
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8 Outer membrane is continuous with rough endoplasmic recticulum on that ribosome is present. And to form the transport vesicle to golgi bodies .
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Inner membrane consist the thin filament (lamin protein )its dense lined with it is called nuclear lamina. Its on nucleoplasm . It gives mechanical support to nuclear envelope and serve site for attachment of chromatin fibers at nuclear periphery
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NUCLEAR PORE Nuclear pore act
as channel for transporation between cytoplasm and nucleus .
It shows that sort of cylindrical is called annulus two distinct annuli outer and inner annuli .Made up to 8 to 9 granules ( diameter 100 to 250 Å ) .
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Annuli arranged ring like structure and inbetween the outer and inner ring on its side walls finger like projection .
With in the pore centeral grannule is present with a diameter of 40 to 300Å act as transporter .
Entire structure is called cart wheel . Nuclear pore has basket like apparatus
called the nuclear pore complex . This complex fills the pore like a
stopper , projecting into both cytoplasm and nucleoplasm.
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FUNCTIONS OF NUCLEAR ENVELOPE
Exchange of material : many substances have to cross the nuclear envelope to reach the nucleus from the cytoplasm and vice versa .
1) These substances are ions and small molecules for example nucleotides , macromolecule such as nucleoprotein and aggregates of ribonucleoprotein particles 145 A◦ less than pore . 2) These passage is depends on their size . 3) There are two steps .BINDING, TRANSLOCATION .
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BLEBBING : Nucleocytoplasmic exchange could be directly through the nuclear bilayer by continuity of endoplasmic reticulum .
Small sacs is developed by outpushing of nuclear envelope on vesicle is formed is called blebbing .
It provides a sites for attachment for chromatin fibres heterochromatin .
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NUCLEAR SAP (NUCLEOPLAMM) It is a semifluid substance present in the
nucleus . It is bounded with nuclear envelope . The nucleoplasm has a complex chemical
composition. Nucleic acids : The most common
nucleic acids of the nucleoplasm are the DNA and RNA.
1) Both may occur in the macromolecular state or in the form of their monomer nucleotides.
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PROTEIN HISTONE
Known as basic It composed of
amino acid arginine , histidine, lysine .
NON HISTONE
Known as acidic
The most abundant acidic proteins of the euchromatin are the phosphoproteins.
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ENZYME Most of the nuclear enzymes are composed
of non-histone(acidic) proteins. DNA polymerase , RNA polymerase,
NAD Synthetase , Nucleoside triphosphatase , Adenosine diaminase , Nucleoside phosphorylase , Guanase , Aldolase , Enolase , 3-phosphoglyceraldehyde dehydrogenase, Pyruvate kinase.
Co –enzyme ATP and ACETYL CoA.
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Helps the nucleus to keep its shape .
when the nucleus is subjected to a moderate high temperature (37◦ c) the nuclear envelope get solubilized , chromatin is solubilized with high salt concentration ,and nucleic acid are digested by nucleases ,the network fibrils is retaining the shape of the nucleus remains .
This network fibrils is known as nuclear matrix . It regulate transcription and replication of DNA.
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NUCLEAR MATRIX
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CHROMATIN
During the interphase nucleus found a number of fibrillar structures that constitute a network called chromatin fibrillar or chromonemata .
Such chromatin becomes thick ribbon like structure is called chromosome .
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Chromatin is a tight complex formed between eukaryotic DNA and nucler protein .
The key protein in chromatin involved in orderly packing eukaryotic DNA are the basic protein (histones) is positive charge and it bind to negatively charged DNA .
There are five basic classes of histones molecule known as H1, H2A, H2B, H3, H4 .
When interphase nucleus is observed under electron microscope it appears like a BEADS ON STRING .
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BEADS ON STRING
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The DNA in a chromatin is very tightly associated with histones that packages its repeating structural units called nucleosome .on that 200bp .
Nucleosome – DNA – WEDGE SHAPED HISTONE OCTOMER – linker DNA - nucleosome core particle .
Non histones chromosomal protein are also associated with chromatin . But not take part in basic structure . Role in regulation of expression of specific genes.
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EUCHROMATIN
light stained Diffused region High amount of RNA Low amount of DNA
HETEROCHROMATIN
Dark stained Condensed region High amount of DNA
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NUCLEOLUS Morphologically it appears spheroid shape
. Size can vary from 1to 5 micro meter . Depends the species no . Of nucleolus . Its is acidophilic .
Male kangaroo – singleFemale kangaroo-two
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COMPONENTS During the cell division on early it
gets disappear and later at the time of daughter nuclei formation it will appear –pars amorpha .
Permanent component does not disappeear persistant thoughout the life cycle . Its filamentous attach RNA – nucleolonema .
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ULTRASTRUCTURE OF NUCLEOLUS
Granular portion being made up of dense granules arranged peripherally and measuring about 150-200 A in diameter . It consists of ribonuclei protein .
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Fibrillar portion having the fibrils of 50-80A length and composed of ribonucleoprotein. This region is also known as nucleolonema. It generally occupies the central region of the nucleolus .
The nucleolus has no limiting membrane and the calcium ions are believed to maintain the intact organization of the nucleolus .
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NUCLEOLAR ORGANIZER (rDNA) Heterochromatin region is found associate
with nucleolus to consitute nucleolar organizer .
The 18S, 5.8S and 28S RNAs are synthesized in the nucleolus .
The nucleolar organizer is usually located in a secondary constriction on the chromosome.
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FUNCTION OF NUCLEOLUS HELPS TO SYNTHESIS OF RNA – It help to synthesis to protein by
the formation of ribonucleic acid . large amount of protein synthesis
if it has high RNA content so large nucleoli . AS AN INTERMEDIATOR OF GENETIC
INFORMATION FROM GENERATION TO ANOTHER .
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QUESTIONS
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THANK YOU