Nucleus and Its Chromosomes

NUCLEUS AND ITS CHROMOSOMES

Structure

1. It is a spherical structure (10 μm dia meter) surrounded by a relatively permeable membrane called nuclear membrane (or envelope). This is composed of two unit membranes and show large pores of 1000 Å diameter which are closed by thin homogenous membrane. Therefore, passage of macromolecules like RNA can take place through these pores. The space between the two folds is 300 Å and is called Perinuclear Cistern.

2. It is made up of chromosomes (each chromosome is made up of supporting protein plus giant molecule of Deoxyribonucleic Acid DNA), on which genes are present. Gene is a portion of DNA molecule which carries a complete blue print for all the heritable species and individual characteristics of an animal. During cell division, the pairs of chromosomes become visible, but between cell divisions the irregular clumps of dark material called chromatin are the only evidence of their presence.

3. It contains a nucleolus which is densest of all the nuclear material i.e. a patch work of granules rich in Ribonucleic Acid (RNA). Nucleoli are most prominent and numerous in growing cells. It synthesizes the RNA for the ribosomes.

FUNCTIONS

1. DNA in nucleus serves as a 'template' (block) for synthesis of RNA, which then moves to the cytoplasm where it regulates the synthesis of protein by the cells. The information coded into the DNA molecules are conveyed from the nucleus to the cytoplasm by messenger RNA where actually the synthetic work of the cell takes place. 

2. Genes are units of hereditary characteristics.

3. It is concerned with cellular reproduction and multiplication; the development of chromosomal threads form the network, being the first step towards cell division.