draw the nucleus of a cell and name the two components of chromosomes mention the role of nucleus pore
Answers
The following points highlight the five main components of the nucleus. The components are: 1. Nuclear envelope 2. Nuclear Sap or Nucleoplasm 3. Nucleolus 4. Chromatic Reticulum 5. Chromosomes.
Nucleus: Component # 1. Nuclear Envelope:
The nuclear membrane or karyotheca is the outer boundary of the nucleus. It is found in the nuclei of all the eukaryotic cells. Electron microscopy has revealed that it is composed of two concentric unit membranes, an outer membrane and an inner membrane of lipoproteins (Fig. 8.2). According to Du Praw, each membrane is about 80-100 Å thick. The outer and inner membranes are separated by a clear space of 100 to 150 Å.
Nucleus: Component # 2. Nuclear Sap or Nucleoplasm:
The undifferentiated protoplasm or ground substance present inside the nuclear envelope is called nuclear sap or nucleoplasm or karyolymph. The nucleoplasm seems to contain granules of various sizes and densities and is yet of unknown composition and function.
Nucleus: Component # 3. Nucleolus:
It is an intranuclear organelle of eukaryotes. The term nucleolus was coined by Bowman (1840). It occurs as a spherical, acidophilous structure suspended in the nucleoplasm either in central or eccentric position. The nucleolus is found in close association of a specific chromosome at a fixed point called nucleolus-organising region.
Nucleus: Component # 4. Chromatic Reticulum:
In the nucleoplasm a dark staining network is seen which is termed nuclear reticulum or chromatic reticulum. The threads of reticulum are formed of chromatin. The chromatin network can easily be seen in the interphase nucleus under compound microscope. During the cell divisions chromatin fibres become thick ribbon-like structures and are called chromosomes.
Nucleus: Component # 5. Chromosomes:
The term chromosome refers only to the deeply staining DNA containing bodies observed in dividing cell of nucleate organisms. Chromosomes are nuclear components possessing a special organization, individuality and function. They are capable of reproducing themselves without change of morphology and physiologic behaviour in successive generations.
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