MINISTRY OF DEFENCE

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  MINISTRY OF DEFENCE. Establishment Of National University In Islamabad Total position. 29 Domicile , All over Pakistan    Qualification  intermediate to bachelor positions . Project Engineer(Civil) account Officer  supervisor assistant office boy     How to apply.   Apply online through the link https://www.fgei-cg.gov.pk/nup-rec.php   Last date to apply  02 April 2023. No TA/DA Fo Interview 
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Nucleus

Nucleus

Nucleus




Robert BrownThe title of the discovery of the Nucleus goes to Robert Brown in 1831, it looks dark than the surrounding cytoplasm. the shape of nucleus may be spherical or irregular.
it controls the life and activities of the cell,in animal it is present in centre of cell but in plant it is pushed towards a side due to large vacuole. the number of nucleus is different in different cell.
mononucleate
the cell have one nucleus.
 Binoculeate:
 Cell have two nuclei.
 Multinucleate:
The cell with more than two nuclei.

The nucleus is visible only during the non dividing phase.

Chemically the nucleus is composed of DNA,RNA and protein including enzymes.


 nucleus is composed of four  parts
1 Nuclear membrane:
 it separates the nuclear material from the cytoplasm,it is not a complete barrier, It contains pores called nuclear pores.over 3,000 nuclear pores are present in egg but erythrocyte have  only 3 to 4 pores.
Certain substances pass like protein and mRNA freely through these pored between the nucleus and the surroundings cellular substances.
 2.Nucleolus:
 One or more small bodie are found called nucleolus,it consists of protein and RNA.
it produces ribosomes.
3 Nucleoplasm:
Fluid lying inside the nuclear membrane is known as *nucleoplasm* .

 *chromosomes*

 Nucleus contain chromatin material this chromatin material is changed into chromosomes during cell division,each chromosomes is made up of protein and DNA.
Dna strand is about 2m long,DNA is wrapped around the core of histone protein to form a nucleosome,histone proteins are( H1 H2a H2b H3 H4 ) about 25 millions nucleosomes are present in each nucleus.
Thus,the structure of Chromosomes the chromosomes looks like a string of beads.
During cell division the coiling around histone is loosened  by acetylation of the histone proteins. chromosomes are visible only during cell division, chromosomes contain units of heredity called genes (segment of the DNA),except in germ cell the chromosomes occur in pairs,one pair originally from each parent.

Function of nucleus 
The specific functions performed by the nucleus are as follows:
I) It is regarded as the controlling centre of the vital activities of the cell, it actslike a brain of cell.
 ii) It controls or directs the synthesis of the enzymes which catalyse most of the reaction in the cell.
iii) It produces chromosomes during cell division,the chromosomes transfer heredity character from parents to daughter cell.
iv) It directly takes part in cell division and reproduction.
v) It produces DNA and RNA,DNA is a genetic material and RNA takes part in protein synthesis.

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