Describe in detail about Nucleus of the cell, its inclusions and functions
Nucleus is
specialized protoplasmic body much denser than the cytoplasm and is commonly
spherical or oval in shape. It always lies embedded in the cytoplasm. Nucleus
is universally present in all living cells. In the higher plants there is
single nucleus in each cell, while in many algae and fungi numerous nuclei may
be present. In lower organisms like bacteria and blue green algae true nuclei
are absent but there is a corresponding nuclear material. Nuclei may vary
widely in sizes from 1 to 500 microns. A nucleus can never be newly formed but
it multiplies in number by division of the pre existing one.
STRUCTURE
Each nucleus is
surrounded by a thin transparent membrane known as the nuclear membrane which
separates the nucleus from the surrounding cytoplasm within the membrane,
completely filling up the space. There is a dense but clear mass of protoplasm
known as the nuclear sap or nucleoplasm.
Suspended in the
nucleoplasm there are numerous fine crooked threads loosely connected here and
there forming a sort of network called the nuclear reticulum or chromatin
network. The threads are made of a substance known as chromatin or nuclein
which is strongly stainable.
The chromatin or
nuclein is a nucleoprotein. One or more highly refractive relatively large and
usually spherical bodies may be seen in the nucleoplasm. These are known as the
nuclei.
CHEMICAL
POSITION
Chemical
position of nucleus is more or less similar to that of the cytoplasm. The
nucleus however is predominantly composed of nucleoprotein which is made of
phosphorus containing nucleic acids and certain specific types of proteins. All
plant proteins contain C, H, O, N and S and sometimes P. Two important nucleic
acids are DNA (Deoxyribo nucleic acid) and RNA (ribo nucleic acid). DAN occurs
in the nuclear reticulum and RNA in the nucleolus, chromosome and cytoplasm.
Nucleus also contains some amount of lipids, particularly phospholipids.
Inorganic salts such as those of Ca, Mg, Fe and Zn are also present in the
nucleus.
Nucleic acids
are universally present in the nucleus and in the cytoplasm of all living cells
and form the chemical basis of life. They are very complex organic compounds
made of phosphate, 5 carbon (pentose) sugar (ribose in RNA) or (Deoxyribose in
DNA) and nitrogen bases.
DNA AND RNA
DNA and RNA
particularly the former are now known to be most important constituents of
living cells. RNA occurs in the nucleoli chromosomes are cytoplasm (about 90%
of the cells RNA occur in the cytoplasm) while DNA occurs in the chromosomes
(nuclear reticulum). They are related chemically, consisting of 5 carbon ribose
sugar and phosphate but DNA has deoxyribose with one less oxygen atom in its
molecule. Both are large molecules or macromolecules but DNA is a double
stranded molecule while RNA is singled stranded one. All secrets of life are
embodied in DNA or in other words it is the chemical basis of life. DNA is the
controlling centre of all the vital activities of the cell. DNA is sole genetic
(hereditary) material (migrating intact from generation to generation through
the reproductive units or gametes and is responsible for the development of
specific characters of a plant. It also controls the biosynthetic processes of
the cell including protein synthesis. RNA is a chemical messenger and plays a
key role in the process of protein synthesis.
FUNCTIONS
Nucleus is
controlling centre of vital activities of the cell in many ways.
(1) Nucleus takes
direct part in reproduction.
(2) Nucleus
takes initiative in cell division.
(3) Nucleus is
the bearer of hereditary characters.
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