Nucleus

occurrence - structure

1. NUCLEUS By, K.ThangaMallika , I M.Sc., Microbiology

2. INTRODUCTION The nucleus was the first organelle to be discovered. It was first observed by ANTON VAN LEEUWENHOEK (1632 - 1723). In more detail in 1831 by Scottish Botanist ROBERT BROWN was observed and named it as “ aerola ” or “nucleus”.

3. OCCURENCE OCCURRENCE - Found in all eukaryotic cells of plants and animals. EXCEPTIONS - Mature sieve tubes and erythrocytes. Prokaryotes (Bacteria) lack true nucleus. POSITION - Usually at the centre but it can change its position according to the metabolic state. NUMBER - Mononucleate , Binucleate and Polynucleate cells.

4. SHAPE AND SIZE : Its shape is related with the shape of the cell. It may be spherical or ellipsoidal. Its size is related with number of the chromosomes. Eg : small in haploid cell and large in diploid cell. Its size also depends upon the volume of the cell, amount of DNA, proteins and metabolic phase of the cell.

5. ULTRA STRUCTURE Larger organelle of the cell. Approximately 6 micrometer in diameter. Occupies about 10% of total volume of cell. DIFFERENT PARTS : Nuclear Envelope Nuclear lamina Nucleoplasm Chromatin fibres Nucleolus

6. NUCLEAR ENVELOPE : Nuclear membrane, outer most covering of nucleus. It acts as a barrier to prevent macro molecules from diffusing freely between nucleoplasm and cytoplasm. It contains 2 cellular membranes: 1.Inner membrane 2.Outer membrane .

7. They are arranged parallel to one another . The space between 2 membranes – perinuclear space. The outer membrane is continuous with the membrane of golgi body, mitochondria, Endoplasmic Reticulum, also studded with ribosomes . Nuclear membrane is not continuous but broken at regular intervals, these broker areas are known as Nuclear Pores.

8. Inner nuclear membrane : 5 to 10 mm thick. It contains Proteins. It acts as a main dwelling for many inner nuclear membrane pores. Outer nuclear membrane : perinuclear space occupies 10 to 500 mm diameter. It continues with Endoplasmic reticulum, studded with ribosomes . It also contains fibres , lipid droplets, crystalline deposits.

9. a. NUCLEAR PORES: Nuclear membrane is not continuous but broke at regular intervals, these broken areas are known as Nuclear pores. They can vary in number and it depends on species and types of the cell. Eg : Mammalian cell has 3000 to 4000 pores. The pores are circular structure and it consists of Annuli.

10. 2 . NUCLEAR LAMINA: Mostly composed of lamina proteins, which synthesized in the cytoplasm and later transported into nucleus. Lamin : Fibrous protein providing structural function and for the cell nucleus. The lamin may be involved in the functional organization of the nucleus. They may play a role in assembly and disassembly before and after mitosis.

11. 3. NUCLEOPLASM: The space between nuclear envelope and nucleolus is filled by a transparent, semi solid granular substance is known as nucleoplasm . It is composed of nucleo protien and contains inorganic and organic substances. It is similar to cytosol .

12. 4. CHROMATIN FIBRES : Chromatin is a mass of DNA and proteins that condense to form chromosomes during cell division. Chromatin is an essential part of genetic makeup of eukaryotic cells, by controlling replication, cell function and storing genetic information. The basic structure for chromatin if the NUCLEOPLASM.

13. 5. NUCLEOLUS: It is composed of the main products of the rRNA genes, as well as their proteins and enzymes. It is a large spherical and acidophilic dense granule. Size depends on the synthetic activities of the cell. Malfunction can leads to several human diseases.

14. FUNCTIONS The nucleus contains most of the cell nucleus in the form of chromatin. The chromatin then organize into chromosomes during cell division. The chromosome contains a set number of genes and it controls every single trait. It controls all the activities inside the cell such as cell growth, metabolism, protein synthesis. It has instructions for making proteins and other molecules.

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