1. Ultra structure of nucleus By: Ms Trupti Marakana

2. Introduction The most prominent features of a cell when viewed under the microscope are the nucleus. Robert brown (1831) discovered for the first time a prominent body within the cell and term it nucleus. it is the Greek word Karyon.

3. Conti.. Location: Every eukaryotic cell (at interphase) contain at least one, almost spherical,dense,highly specialized commanding body called nucleus. Exception: mature phloem sieve tube element in plant and mature red blood cells of mammals, bacteria and cyanobacteria etc. Karyology:- all the functional activities of cell are controlled with the study of nuclei is called Karyology.

4. Conti.. Eukaryotic cell uninucleated Dikaryotic also, e.g.- in some fungi- puccinia, at certain stage if life cycle. Chemically nucleus consists of approximately 80% proteins, 20% DNA, 5% RNA and 3% lipids

5. Nuclei are conspicuous because they are the largest of cell organelles. Metabolically active cells have large nuclei in proportion to cytoplasm.

6. Shape It varies in different stage. Normally remains related with the shape of the cell. Flattened squamous epithelium cells having disc shape nucleus. Spherical, cuboidal, or polyhedral cells having spherical nucleus. Columnar cell having ovoid shape nucleus.

7. Conti.. In WBC nuclei are bi-lobed or multi-lobed. In ciliated protozoa the nucleus shows a variety of shape.

8. size The size of nucleus is variable but in general it bears some relation to that of the cytoplasm. Size is depends upon its Protein and DNA content as well as volume of the cell. Size is also varies in different cells. Haploid cell having small sized nuclei. Diploid cell having large sized nuclei.

9. Number Nucleus is present in almost in higher cells. Most plant and animal cells usually have a single nucleus and are to be mononucleate. Some cells of liver and cartilage have two nuclei called as bi-nucleate. The cell which contain 3 to 100 nuclei called as polynucleate.

10. Conti.. In plant cell it is polynucleate condition called as coenocytes e.g.- vaucheria and certain fungi. In animal cell it is known as Syncytial. E.g. - polykaryocytes bone marrow.

11. Structure (main four part) 1)- nuclear envelope 2)- nucleoplasm 3)- chromatin 4)- nucleolus

12. Structure of nucleus

13. 1- Nuclear envelope or Nuclear membrane (NM)

14. It is a porous double membrane surrounding the nucleus. It consists of two concentric unit membranes with a narrow (200-400 angstrom wide) fluid- filled inter membrane. The perinuclear space which is continuous with the lumen of rough endoplasmic reticulum(RER) because of the attachment outer layer with endoplasmic reticulum.

15. Conti. The outer membrane’s outer surface is studded with ribosome. NM is perforated by minute circular nuclear pores (1,000 – 10,000 pores per nucleus). A mammalian cell contains 3,000 – 4,000 pores per nucleus. Each pore is surrounded by a large disc like structure known as the nuclear pore complex.

16. Conti. The continuity of inner and outer membrane enables the flow of lipid soluble materials from endoplasmic reticulum to inner nuclear membrane. The hole in the centre of the pore complex provides the main channel (90 to 100 angstrom) through which water soluble molecules shuttle between the nucleus and cytoplasm. This channel is contains a protein – nucleoplasmin which facilitates the nucleocytoplasmic traffic through the pore.

17. Conti. Definition and function:  Nuclear lamina:- A fibrous protein network called nuclear lamina. Which lines the inside of inner nuclear membrane. It helps to shape the nucleus, organize its chromosomes and holds nuclear pores in place.

18. 2- Nucleoplasm Definition : the space between the nuclear envelope and the nucleolus is filled by a transparent, semi- solid, granular and slightly acidophilic ground substance or the matrix is called as nucleoplasm.

19. Conti.. Nucleoplasm is clear, gel like ground matrix containing a variety of chemicals including ions, proteins(including enzymes) and nucleotides in colloidal solution. The most common nucleic acids of nucleoplasm are DNA and RNA. Both may occur in the macromolecular.

20. Conti. The nucleoplasm contain many type of complex protein (basic protein or acidic protein). The nucleoplasm also contains many enzymes for synthesis of DNA and RNA.

21. 3- Chromatin Definition: “it is a material which comprises in the thread like bodies forming a network composes of coils of DNA bound to basic protein histones.” Histones are found only in the nucleus and being basic proteins interact strongly with deoxyribonucleic acid.

22. Conti.. Histones occupy the major grooves of DNA at the angle of 30 degree. The histone proteins are rich in Lysine and Arginine amino acids.  Function of histone: (I) Provide structural proteins for stabilizing chromosome structure (II)To neutralize anionic charge of inter nucleotide phosphate in DNA.

23. Conti.. Kornberg and Thomas (1974) showed that each nucleosome bead consists a set of eight histone molecules, which form a octamer around which the double stranded DNA is wound. Such chromatin fibres are observed only in the interphase nucleus. During cell division(mitosis and meiosis) chromatin fibres become thick ribbon like structure which is known as chromosomes.

24. Conti.. During interphase chromatin remains tightly coiled and called heterochromatin while the remaining loosely coiled called euchromatin. Heterochromatin occurs near the nuclear envelop, while the euchromatin lies towards the centre of the nucleus.

25. 4- Nucleolus Definition: “the nucleus contains a large, spherical and acidophilic dense granule known as the nucleolus.” it is discovered by Fontana in 1781. It was well established in 19 th century that the size of the nucleolus is relates with synthetic activity of the cell.

26. Conti.. One to three conspicuous spherical structures, called nucleolus are closely associated with the inner nuclear envelope. The number of the nucleus depends on the species and the number of chromosomes. It contains large amount of RNA and DNA also. Its chief function is the synthesis of ribosomal RNA. During cell division nucleolus and NM disappear.

27. Conti. Why nucleolus is called as Ribosome producing machines ? Ans. Nucleolus has dense fibrillar region in which portion called secondary constriction organizing regions of different chromosome meet. These portions contain many copy of DNA which direct the synthesis of rRNA.

28. Conti.. Therefore in this region rRNA is synthesized at very fast rate. The protein of ribosomes are synthesized in cytoplasm which diffuse into the nucleus and reach nucleolus. Here rRNA and ribosomal proteins are packed into ribosomal units or precursors or nuclear ribosomes. That is why nucleoli(nucleolus) called ribosome producing machines.

30. Function 1)It contains the genetic information for reproduction, development, metabolism as well as behavior of organisms. It can duplicate this information and also pass it on to the daughter cells. Thus nucleus is the vehicle of heredity. 2)It contains directions for the control of cellular activities (e.g. what enzymes are to be formed and when) through the formation of messenger RNA.

31. Conti.. 3) The nucleolus takes part in the production of ribosomes. 4) It stores all the proteins of ribosome and also rRNA.