● NUCLEUS
1. The nucleus is the most important component of the cell and it controls all functional activities of the cell.
2. The nucleus is also known as karyon and its study is known as karyology,
3. The cell nucleus was discovered by an English botanist Robert Brown in 1831.
4. The nucleus is the primary carrier of hereditary material in the cell.
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6. Hämmerling conducted nucleo - cytoplasmic experiments in two species namely A. crenulata and A. mediterranea which differ in the shape of the cap.
7. Hämmerling's experiments on Acetabularia involved exchanging nucleus.
8. Experiments on Acetabularia by Hämmerling proved the role of nucleus in heredity.
9. The nucleus can be divided into four parts: nuclear membrane, nucleoplasm, chromatin and nucleolus.
1. Nuclear Membrane
10. Nucleus is separated from surrounding cytoplasm by a nuclear envelope (karyotheca) which is double and porous.
11. Perinuclear space is found between outer and inner nuclear membranes.
12. The outer membrane is connected with endoplasmicSYN reticulum and its outer surface may contain ribosomes while inner surface is smooth.
13. The nuclear membrane contains a large number of pores which may be circular or polygonal having a diameter of about 40–100 nm.
14. The nuclear pores are enclosed by circular structures called annuli.
15. The pores and annuli together are called pore complex.
16. Nucleus communicates with cytoplasm through nuclear pores.
17. Structure of nuclear envelope facilitates nucleo - cytoplasmic exchange of materials.
18. Cellular structure which always disappears during mitosis or meiosis is nuclear envelope.
19. Nuclear membrane disappears during mitosis at late prophase.
2. Nucleoplasm
20. The nucleus contains a viscous fluid the nucleoplasm (nuclear sap or karyolymph) which keeps nucleus turgid,
21. Nuclear sap contains enzymes of nucleic acid synthesis like DNA or RNA polymerase.
22. Nucleoplasm does not contain cytochrome oxidase and succinic dehydrogenase. T.
23. Underlying the inner nuclear membrane is the nuclear lamina, a fibrous meshwork that provides, structural sup port to the nucleus.
24. The nuclear lamina is composed of one or more related proteins called lamins.
25. In addition to providing structural support to the nucleus, The nuclear lamina is thought to serve as a site of chromatin attachment.
3. Chromatin
26. Suspended in the nucleoplasm is the chromatin material. In nucleus the hereditary material is contained in chro natin.
27. Chromatin is the interphase chromosomal material, a complex between eukaryotic DNA and protein.
28. The major proteins of chromatin are the histones - small proteins containing high proportion of basic amino acids ( arginine and lysine) that facilitated binding with negatively charged DNA molecule.
4. Nucleolus
29. nucleolus was discovered by Fontana in 1781 and the term 'nucleolus' was coined by Bowman in 1840.
30. Nucleolus is characterized by the absence of limiting membrane, presence of chromatin and granules and fibrils of RNA and protein.
31. There is one nuclcolus for each haploid set of chromo somes.
32. Nucleolus is largely composed of RNA and it stains more darkly than the nucleus. 33. Inside nucleus, the nucleolus is found attached to NOR (Nucleolus Organizer Region).
34. Nucleolus consists of DNA + RNA + Protein.
35. The configuration of nucleolus is maintained by calcium.
36. Nucleolus disorganises itself during late prophase and reappears during telophase.
37. The messenger RNA is formed inside the nucleus but outside nucleolus.
38. Nucleoli are very important since they are the sites for ribosomal RNA (r - RNA) synthesis.
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