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iPRESENTED BY K.SIVARAJ ,shansiva1996@gmail.com

NUCLEUS

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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 .

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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