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Can anyone say about nucleus and its components

Can anyone say about nucleus and its components

Grade:9

1 Answers

deapan
131 Points
8 years ago
NUCLEUS
 
                                        Nucleus is double membrane bound dense protoplasmic body that controls cellular metabolism, enclose all the genetic information and is able to transmit it to the next generation. Nucleus is the largest organelle by occupying 20% of cell mass. Nucleus is the control centre and largest organelle of the cell.
                                        It stains deeply, mostly spherical. Normally a cell contains one nucleus this condition is called Uninucleate , Mononucleate or monokaryotic. Sometimes a cell contains two nucleus this condition is called Binucleate /Dikaryotic.
                                        The nucleus of bacteria is not developed like multicellular organisms. The cells which have nucleus without nuclear membrane is called Prokaryotic cells. Prokaryotes have incipient nucleus devoid of nuclear membrane, nucleolus and histone. Such type of nucleus is called nucleoid. Nucleus is rounded in young plants, polygonal in animal cells, oval or elliptical in matured plant cells.  
                                        The liquid protoplasm in the nucleus is called nucleoplasm  which consist of nucleolus and chromatin reticulam bounded by a double membrane called nuclear membrane. DNA and RNA are found in nucleus. In a growing or differentiating cell, the nucleus is metabolically active, producing DNA and RNA. The RNA is exported through the nuclear pores to the cytoplasm for use in  protein synthesis. In ‘resting cell’ the nucleus is inactive or dormant and minimal synthesis of DNA and RNA takes place.
                                        Nucleus of undividing cell is called interphase nuleus. WBC have lobedd nuclei. Except mature mammalian RBC and sieve cells of phloem others contain nucleus, brain cells contain single nucleus and paramoecium contains 2 nuclei. Blue green algae does not possess nuclear membrane The only plant cells without nucleus is xylem vessels.
NUCLEAR MEMBRANE
                                        The nucleus has a double layered covering called nuclear membrane which is interrupted by large number of pores. Each one is a phospholipid bilayer containing many different types of proteins. The inner nuclear membrane defines the nucleus itself. In many cells the outer nuclear membrane is continuous with the rough ER and the space between the inner and outer nuclear membrane is continuous with the lumen of the rough ER.
                                        The two nuclear membranes appear to fuse at the nuclear pores. These ring like pores are constructed of a specific set of membrane proteins and these act like channels that regulate the movement of substances between nucleus and cytosol.
                                        The nuclear membrane has pores which allow the transfer of material from inside the nucleus to its outside, that is, to the cytoplasm. Membrane is made up of lipids and proteins and has ribosomes attached on the outer membrane that makes them rough. It keeps then hereditary material in contact with the rest of cell
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                                        A sub g of the nucleus, the nucleolus is easily recognized under light microscope. These are membrane less, spheroidal bodies present in all eukaryotic cells except in sperm cells and some algae. It stains uniformly and deeply. Most of the ribosomal RNA of a cell is synthesized in the nucleolus so it is called as Ribosome factory. The finished or partly finished ribosomal sub units pass through a nuclear pore into the cytosol. It has DNA, RNA and proteins. It regulates synthetic activity of the nucleus. It disappears during cell division and reappears in the daughter cells.
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                The non nucleolar regions of the nucleus is called nucleoplasm. It has very high DNA concentration. Fibrous proteins called lamins form a two dimensional network along the inner surface of the inner membrane giving it shape and apparently binding DNA to it. During the early stages of cell division breakdown of this network occurs  
CHROMATIN
In the nucleo plasm or karyolymph, fibrillar structures form a network called chromatin fibrils, which gets condensed to form distinct bodies called chromosomes during cell division. On staining the chromosomes, two regions can be identified in the chromatin material heterochromatin dark and autromaticn (light). Heterochromatin has less DNA and genetically less active than euchromatin which has more DNA and genetically more active. Number of chromosomes is fixed in an organism. During cell division chromosomes divide in a manner that the daughter cells receive identical amounts of hereditary matter.

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