NUCLEUS:STRUCTURE AND FUNCTION:

NUCLEUS: STRUCTURE AND FUNCTION:

DISCOVERY:

Nucleus was discover by ROBERT BROWN IN 1831
                           Nucleus is the most prominent and most important part of the cell

PRESENCE:

In animal cell it is found in the centre of cell (except muscel fibre cell). In plant cell it is slightly away from the centre of cell due to presence of large centeral vacule

PARTS:

A typical eukaryotic nucleus consist of
1-Nuclear envelope
2-Nucleoplasm
3-Nucleoli
4-Chromatin

NUCLEAR ENVELOPE:

Nuclear envelope also called nuclear membrane is a double membrane which makes the boundary of the nucleus. Both membrane of nuclear envelope are seperated by fluid-filled PERINUCLEAR SPACE. The membrane are composed of lipid bilayer and protens. The outer membrane of nuclear envelope is covered with ribosomes and connected with membrane of ER. There are many pores in the nuclear envelope called NUCLEAR PORE. Nuclear pores consist of special transport protein called NUCLEOPORINS. AT the point of nuclear pores both membranes are interconnected. Smaller molecule can simply diffuses through the pores, larger molecules may be recognized by special signal sequences and then diffused with the help of nucleoporins into or out of the cell

FUNCTION OF NUCLEAR PORES::

Nuclear pores regulate nucleo-cytoplasmic exchange of materia. This exchange include RNA and ribosomal protein moving from nucleus to cytoplasm and protein (such as DNA polymerase), carbohydrates, signalling and lipid moving from cytoplasm to nucleus

NUCLEAR LAMINA:

Except nuclear pores, the nuclear side of nuclear envelope is lined by net like array of protein filaments

FUNCTION OF NUCLEAR LAMINA:

It maintain the shape of nucleus by mechanically supporting the nuclear envelope

NUCLEOPLASM:

Nucleoplasm is the transparent semifluid ground substance formed of a mixture of proteins, enzymes (DNA and RNA polymerase), free nucleotide and some metal ions (Mg) for the synthesis of DNA and RNAs. It also contains histone and non-histone protein . SO the nucleoplasm is slightly different from cytoplasm

NUCLEOLUS:

nucleolus, (plural:nucleoli) is a non-membrane bound structure in the nucleoplasm.  A cell may have one or more NUCLEOLI. Nucleolus appear during cell devision
          A nucleolus consist peripheral granular area(contain ribosomal subunit) and a centeral fibriler area (contain rRNA andrDNA). Therefore, nucleolua is involved in the construction of ribosome

CHROMATIN AND CHROMOSOME:

Chromatin is a network of thin thread like filament made up of DNA and associated protein molecules. During cell devision chromatin fibre begin to condense and coil up into separate structure called CHROMOSOME, which are thick enough to be seen with a light microscope
A typical chromosome consist of two strands called CHROMATID which are attached with each other at point known a CENTROMERE. The centromere lies within a thinner segment of the chromosome called PRIMARY CONSTRICTION. The centromere is a constriction function.ally related to the movement of chromosomes during cell devision Each centromere has two plaques of protein called KINETOCHORES that are oriented on the apposite directionsides of the constriction. Each kinetochore forms the site of attachment fo a single microtubule during cell devision. Some chromosome may have another point of union along the length of chromatids, called SECONDARY CONSTRICTION orNUCLEOLAR ORGANIZER. It gives rise to nucleoli during interphase . At least one pair of homologeous chromosome possesses nucleolar organizer . Beside secondary constriction the end become knob like like structure called SATELLITE