2. GENERAL INTRODUCTION Most significant component It controls metabolic and hereditary activities of the cell,so that it referred as “control center” It contains DNA with complex of large variety of proteins-histones to form chromosomes The genes within the chromosomes are the cell’s nuclear genome It contains nucleic acid(DNA,RNA),nuclear protiens,nuclear enzymes(e.g. DNA polymarase,RNApolymarase, endonuclease, exonuclease,ligase etc.
3. HISTORY 1831:Robert Brown [while he was studying orchid’s outer layer,he observed an opaque area which he called Nucleus] 1838:Mittehias Schleiden [proposed that the nucleus plays a role in generating cells,introduced name Cytoblast(cell builder)]
4. Occurrence and position Found in eukaryotic cell of the plants and animals,absent in mature sieve tubes of higher plants, mammalian erythrocytes and bacteria Located in the centre of the cell,but its position may change from time to time according to metabolic states of the cell no. of the nucleus: -single nucleus(mononucleate) -two nuclei(binuleate) -more than two(polynucleate) Syncytial cells : in animals(e.g.osteblast,straited muscle fibers) Coenocytic cells: in plants(e.g.siphonalalgae,certainfungai)
5. Shape and size Its shape is related with the shape of the cell -certain irregular -spheroid nuclei in isodiametrical cells -ellipsoid nuclei in cylindrical,prismatic or fusiform cells Its size is related with no. of the chromosomes e.g.small in haploid cell and large in deploid cell The size is also depends upon the volume of the cell,amount of DNA,proteins and metabolic phase of the cell
6. Ultra structure Largest organelle of cell. Approximately 6µm in diameter. occupies about 10% of total volume of cell. Different parts: Nuclear envelope Nuclear lamina Nucleoplasm Chromatin fibres nucleolus
11. 2. Nuclear lamina Mostly composed of laminproteins,which synthesized in the cytoplasm & later transported into nucleus. The lamin monomer contains helical structure , 2 monomers coiled around each other & form dimer-coiled coil. 2 of these dimer join side by side in an antiparallelarrangment form tetramer-protofilament 8 of these filament arranged laterally & twist to form rope like filament 3. Nucleoplasm The space between nuclear envelope & nucleolus is filled by a transparent,semisolid,granular & acidophilic ground substence is known as nucleoplasm. Nuclear components:-chromatin threads & nucleolus suspended in it. It is composed of nucleoprotein & contains inorganic & organic substances like nucleic acid, proteins, enzymes & minerals
12. 4. Nucleolus It is a large spherical & acidophilic dense granule also called suborganelle Discovered by Fontona in 1781 Size is depend on synthetic activities of the cell Main function is to synthesize r-RNA & produseribosomes 5.Chromatin fibres The nucleoplasm contains many thread like coiled & much elongated structure –chromatin fibres Observe only in the interphase During cell division it become thick called-chromosome chromatin fibres are of 2 types: Heterochromatin: more compact DNA form Euchromatin: less compact DNA form
