Nucleus

Nucleus (head quarter of cell)

                    

• It is discovered by Robert brown in 1831.
• It is a Greek word which mean  karyon in orchid cell.
• Nucleus is considered as controller or director of cell.
• Nucleus is a double membrane bound organelles which control all cellular metabolic activity and contain genetic information.

Number

1. Same cell can absent nucleus called Enucleated cell. EXAMPLE - Human RBCs, Sieve tube, Cell platelets.
2. Almost all eukaryotic cell have only one nucleus is called Uninucleated cell like Animal cell.
3. Having two nucleus is called by nucleated cell is called Binucleated cell.EXAMPLE - Paramecium(2 nucleus-> 1. Macronucleus   2. Micronucleus)
4. Contain more than two nucleus is called Multinucleated cell.EXAMPLE - Opilina, skeleton muscle cell.

Position of nucleus :

Centric -  Nucleus present in centre of cell. EXAMPLE - Almost all animal cell.

Ecentric -  Nucleus is shifted from the centre but not closer to plasma membrane. 

EXAMPLE - Plant cell.

Peripheral - Nucleus is present just closer near plasma membrane.

EXAMPLE - Adipocytes.

Basel - Nucleus is present at the base of cell.

EXAMPLE - Columnar cell & Goblet cell.

SHAPE OF CELL 

1 Circular (in almost all Eukaryotic cell)

         

            

2 Oval (in smooth muscle cell) 

       

3 Horseshoes shape (eg : varticella)

4 Bilobed (eg : eosinophil) 

5 Trilobed (eg: basophil)

6 Multilobed (eg: neutrophil)

                       Structure of nucleus 

Nuclear membrane :

Nuclear membrane is also called Nuclear envelope / karyotheca.

• Nucleus is surrounded by two membrane, that separate Nucleoplasm from cytoplasm. 
• Nuclear membrane has minute pores called nucleopore.
• Nucleopore help in exchange of different substance between nucleoplasm and cytoplasm.

Nucleoplasm :

Nucleoplasm is also called Nuclear sap / karyonlymp.

• It is a part of protoplasm which is enclosed by nuclear membrane.
• It contain chromatin fibre and nucleolus.

Nucleolus :

It is called Nucleus of nucleus.

• It is a store house of R.N.A., nucleolus is the factory of Ribosomes.
• Calcium uses and cell for maintenance of nucleolus.

NOTE - Ribosome is the protein factor and nucleolus is the factory of ribosomes.

Chromatin fibre :

• D.N.A. + Histone protein are intermingled with each other to form chromatin fibre.
• Chromatin is essentially composed of DNA and basic protein called HISTONE PROTEIN.
• Histone protein or packaging protein, it means negative charged DNA wrapped around positively charged Histone protein.

I M P O R T A N T - histone protein is absent in in prokaryotes. Dinoflagellate contain nucleus is surrounded by a nuclear membrane but, in their nucleus, histone protein is absent,that's why dinoflagellate is connective link between prokaryote and eukaryote.