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                         NUCLEUS

1. Nucleus was discovered by Robert Brown in 1831 from the orchid root cells.

2. The word “Nucleus” was coined by Robert Brown from a Latin word ‘Nucleus’ which means Kernel.

3. Defination – Nucleus is a conspicuous, specialized double membrance bounded organelle which passess the genetic information for controling the metabolism, growth and differentiation of the cell.

4. Account to number and shape of nucleus it is divided into the following types

            i. Mononucleate / Monokaryotic Cell – most eukaryotic cells are monokaryotic, i.e. containes  single nucleus.

            ii. Binucleate Cell – found in Paramecium, cartilage cell, liver cell

            iii.Trinucleate cell – found in Aurelia

            iv. Multinucleate cell – found in Latex Vessel, mucor, rhizopus, vaucheria, striated muscle cells,    prokaryotes, bone marrows(even 100 nuclei).

5.In plant multinucleate stage is called Coenocytic while in animals it is called Syncytium.

 

 

Position

 

1. In embryonic stage it occupies a central position but later may be displaced in plant cell due to central vaccuole.

2. In adipose tissue fat globule displaces nucleus to peripheral position and in glandular cell it occupies basal position.

3. Size of nucleus varies from 5 – 25μm

 

 

Chemical Compositions

 

1. Basic histone Proteins – 15% 

2. Acidic protein, neutral protein & enzyme – 65%

3. DNA – 9 to 12%

4. RNA – 5%

5. Lipid – 3%

6. Mineral elements – traces

 

 

Structure

 

                                     

A typical nucleus has following parts

i . Nuclear Envelope

ii. Nucleoplasm

iii. Nucleolus

iv. Chromatin Thread

 

  • Nuclear Envelope / Karyotheca

1. Under electron microscope, nuclear envelope is seen to have 2 membranes, outer and inner membrane which are separated from each other by peri-nuclear space of 20nm.

2. The nuclear membrane is perforated having nuclear pore complex, which contains a ring or cylinder called as Annulus.

3. In the inner side of nuclear envelope many cell types fibrous material present called the fibrous lamina or internal dense lamella.

4. Outer nuclear envelope communicates with E.R. and has several ribosomes called as Rough Endoplasmic Reticulum.

5. Both inner and outer membrance are trilaminar unit membrance having similar structure to that of E.R, with 7-8nm thickness.

6. Peri-nuclear space filled with fluid similar to that of E.R. Cisternae and anti-bodies have been localized in perinuclear space in lymphoid cells (Produced and Stored there)

7. There are 15 to 30 millions octagonal or circular pores present per nucleus.

8. Nuclear pore complex has 120nm diameter, 50nm thickness and 8 fold symmetry. It consists of annuli a set of large protein grannules arranged in octagonal pattern.

 

  • Nucleoplasm

1. It is transparent, semi-solid, grannular and slightly acidophilic ground subtance of nucleus.

2. Nucleoplasm is the store house of all raw materials and enzymes required for synthesis of DNA, RNA, and ribosome subunits.

3. It provides turgidity to the nucleus, certain proteins present in the nucleoplasm appear to take part in spindle formation.

 

  • Chromatin thread or Nuclear reticulum

1. The long fine thread like fillamentous structure of DNA – histone protine complexes present in the nucleoplasm are known as chromatin fibres.

2. Chromatin fibres are only seen at interphase stage of cell cycle.

3. Chromatin reticulum are of 2 types – 

            i. Euchromatin – Light stained, genetically active

            ii. Heterochromatin – darkly stained condensed, metabolically and genetically inert.

4. Chromatin consists of  DNA-31%, RNA-5%, histone protein-36%, non-histone protein-28%.

 

  • Nucleolus

 

1.It is a spheroidal body situated within the nucleus either in central or peripheral position.

2. It has mainly 4 parts – amorphous matrix, nuclear chromatin, pars fibrosa, pars granulosa.

3. Many lower species like yeast and bacteria lacks nucleoli, ganglion have single nucleolus while liver cells and lymphocyte cells have 2 nucleolus.

4. Nucleosome has main function in RNA production, protein synthesis and ribosome formation.

 

 

 

Function of Nucleus

 

1. Store house of genetic Information – It stores all the genetic information in chromatin as DNA.

2. Transmission of genetic information – It is the site of transmission of genetic information from parent cell to daughter cell and from one generetion to next generation.

3. Cell Division

4. Growth of new cells – Newly formed cell grow in size by accumulation of strutural protine and other organic subtance being produced by the instruction of gene of chromatin.

5. Cell differentiation – Differentiation of cell occurs due to differential functioning of genes of chromatin.

6. Replication, transcription – Both these process are occurs inside the nucleolus as enzymes required for these process are present here.

7. Cellular Metabolism – With instruction of genes of chromatin various cellular metabollic activities are regulated.

8. Genetic Variation – Genetic variation that occur in the genes of the chromatin contribute to organic evolution and creation of new species.

9. Formation of ribosome – It is the site for synthesis of ribosomes.

 

 

PRESENTED BY –

Fanee Mohanty (Lecturer in Botany)

   

 

Fanee Mohanty