NUCLEUS
NUCLEUS:-
Nucleus is a specialized double membrane bound protoplasmic body which contains all the genetic information for controlling cellular metabolism and transmission to the posterity .A nuclues in the non-dividing or metabolic phase is called interphase nucleus .Like other cellular Structure s,living unstained nucleus doesn't show much internal differentiation.
Nucleus is the largest cell organelle .Though first observed by Leeuwenhoek in red blood corpuscles of fish,nucleus was first study in orchid root cells by Robert brown in 1831.
NUMBER--Commonly cells are "uninucleate" that is they posses a single nucleus.
Binucleate- they posses two nuclei found in 'paramecium caudatum'
Multinucleate- it is also known as polynucloid condition which are found in bone marrow, striated muscles,latex vessels etc.
Shape-- the nuclei are generally rounded in outline.They appear oval or elliptical In plant cell .Disc shape nuclei occur in the cells of squamous epithelium.
Position-- Nucleus is usually found in the region of maximum metabolic activity in the cytoplasm.commonly it is situated in the geometric centre of the cell. In plant cells it is pushed to peripheral position on one side due to the development of large central vacuole.
Generally nucleus is made up of 5 parts e.g.
1) Nuclear envelope
2)Nucleoplasm
3)Nuclearmatrix
4)chromatin
5)Nucleolus
1)NUCLEAR ENVELOPE:-
It is also known as karyotheca. It bounds the nucleus on the outside .The nuclear envelope separate the nucleus from the cytoplasm.it is made up of 2 layer .The inner membrane is smooth.The outer membrane may be smooth or it's cytoplasmic surface may bear ribosomes like the endoplasmic reticulum.The two membranes of the nuclear envelope are separated by an electron transparent perinuclear space.the outer membrane is often connected to endoplasmic reticulum.
Nuclear envelope contains a large number of pores or perforations.In some cases 10% of the envelope is occupied by pores.the two membrane of the envelope become continuous in the region of pores.Nuclar pores have complex structure.They may have diaphragm,septum,plug of electron dense material or nucleoplasmin,belbs or annuli. Annuli are circular structure around the pore. The pore and annuli form a pore complex called annulated pore.
2.NUCLEOPLASM:-
It is a transparent semifluid and colloidal substances which fills the nucleus . It contains nucleosides and a number of enzymes like 'DNA polymerase', RNA polymerase',nucleoside phosphorylase. Which are required for the synthesis and functioning of DNA,RNA,nucleoproteins .
3.NUCLEAR MATRIX:-
It is a network of fine fibrils of acid proteins that function as scaffold for chromatin.On the periphery ,below the nuclear envelope,nuclear matrix forms a dense fibrous layer Called nuclear lamina.Nuclear matrix consists of 2 types of intermediate filaments ,lamin A and laminB.
4.CHROMATIN:-
It is a heriditary DNA-protein fibrillar complex which is named so because of its ability to get stained with certain basic dyes. Chromatin occurs in the form of fine overlapping and coiled fibres which appear to produce a network called chromatin reticulum. Chromatin fibres are distributed throughout the nucleoplasm .they are mainly divided into two regions -euchromatin and heterochromatin. Euchromatin is narrow lightly stained and diffused fibrous part which forms the bulk of chromatin. Heterochromatin is wider and darkly stained and condensed granular part which attached with the chromatin.
5.NUCLEOLUS:-
It was first discovered by FONTANA . Nucleolus is a naked,round or slightly irregular structure which is attached to the chromatin at a specific region called
"Nucleolar organiser region " . Commonly 1-4 nucleoli are found in a nucleus .
A covering membrane is absent around nucleolus.calcium seems to be essential for maintaining it's configuration.nucleolus has four components e.g. amorphous matrix,granular part,fibrillar portion and chromatin.
Nucleus is a specialized double membrane bound protoplasmic body which contains all the genetic information for controlling cellular metabolism and transmission to the posterity .A nuclues in the non-dividing or metabolic phase is called interphase nucleus .Like other cellular Structure s,living unstained nucleus doesn't show much internal differentiation.
Nucleus is the largest cell organelle .Though first observed by Leeuwenhoek in red blood corpuscles of fish,nucleus was first study in orchid root cells by Robert brown in 1831.
NUMBER--Commonly cells are "uninucleate" that is they posses a single nucleus.
Binucleate- they posses two nuclei found in 'paramecium caudatum'
Multinucleate- it is also known as polynucloid condition which are found in bone marrow, striated muscles,latex vessels etc.
Shape-- the nuclei are generally rounded in outline.They appear oval or elliptical In plant cell .Disc shape nuclei occur in the cells of squamous epithelium.
Position-- Nucleus is usually found in the region of maximum metabolic activity in the cytoplasm.commonly it is situated in the geometric centre of the cell. In plant cells it is pushed to peripheral position on one side due to the development of large central vacuole.
(Structure of nucleus)
Generally nucleus is made up of 5 parts e.g.
1) Nuclear envelope
2)Nucleoplasm
3)Nuclearmatrix
4)chromatin
5)Nucleolus
1)NUCLEAR ENVELOPE:-
It is also known as karyotheca. It bounds the nucleus on the outside .The nuclear envelope separate the nucleus from the cytoplasm.it is made up of 2 layer .The inner membrane is smooth.The outer membrane may be smooth or it's cytoplasmic surface may bear ribosomes like the endoplasmic reticulum.The two membranes of the nuclear envelope are separated by an electron transparent perinuclear space.the outer membrane is often connected to endoplasmic reticulum.
Nuclear envelope contains a large number of pores or perforations.In some cases 10% of the envelope is occupied by pores.the two membrane of the envelope become continuous in the region of pores.Nuclar pores have complex structure.They may have diaphragm,septum,plug of electron dense material or nucleoplasmin,belbs or annuli. Annuli are circular structure around the pore. The pore and annuli form a pore complex called annulated pore.
(Structure of Nuclear envelope)
2.NUCLEOPLASM:-
It is a transparent semifluid and colloidal substances which fills the nucleus . It contains nucleosides and a number of enzymes like 'DNA polymerase', RNA polymerase',nucleoside phosphorylase. Which are required for the synthesis and functioning of DNA,RNA,nucleoproteins .
(Nucleoplasm structure)
3.NUCLEAR MATRIX:-
It is a network of fine fibrils of acid proteins that function as scaffold for chromatin.On the periphery ,below the nuclear envelope,nuclear matrix forms a dense fibrous layer Called nuclear lamina.Nuclear matrix consists of 2 types of intermediate filaments ,lamin A and laminB.
4.CHROMATIN:-
It is a heriditary DNA-protein fibrillar complex which is named so because of its ability to get stained with certain basic dyes. Chromatin occurs in the form of fine overlapping and coiled fibres which appear to produce a network called chromatin reticulum. Chromatin fibres are distributed throughout the nucleoplasm .they are mainly divided into two regions -euchromatin and heterochromatin. Euchromatin is narrow lightly stained and diffused fibrous part which forms the bulk of chromatin. Heterochromatin is wider and darkly stained and condensed granular part which attached with the chromatin.
5.NUCLEOLUS:-
It was first discovered by FONTANA . Nucleolus is a naked,round or slightly irregular structure which is attached to the chromatin at a specific region called
"Nucleolar organiser region " . Commonly 1-4 nucleoli are found in a nucleus .
A covering membrane is absent around nucleolus.calcium seems to be essential for maintaining it's configuration.nucleolus has four components e.g. amorphous matrix,granular part,fibrillar portion and chromatin.
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