Nucleus of Animal Cell
The presence of the cell nucleus was first reported in 1838 by Robert Brown. Its early Discovery was due to its prominence in many cells where it stands out as slightly darker than the surrounding cytoplasm. They are typically about 10 micrometres and diameter it is one of the most important organically because it controls all the metabolic activities and has the genetic information in the form of chromosome and DNA. They may be irregular or spherical in shape generally the cells having one nucleus mononuclear, those having two nuclei are binucleate and those having more than two nuclei are considered to be multinucleated organism. There are different types of nucleus the parts of the nucleus include nuclear membrane, nucleolus nucleoplasm and last but not the least the most important structure chromosomes.
The outermost membrane of the nucleus is the nuclear membrane which separates the nucleus from the cytoplasm of the eukaryotic cell. The nuclear membrane is actually the nuclear envelope composed of two membranes. The outer membrane is continuous with endoplasmic reticulum why the inner membrane encloses the nuclear contents. These membranes are not continuous living certain pores at the points in nuclear pores. Nuclear force allowed exchange of material between the nucleus and cytoplasm.
Another most important part of the nucleus is that of the nucleolus. It is dark structure body within the nucleus and it is without any membrane-bound to separate it from the rest of the material gear may be one or more nucleoli in the nucleus. It is composed of two regions the peripheral granular area and composed of precursor of ribosomal subunit and Central fibrillar area consisting of large molecular weight RNA and DNA.
Nucleoplasm is the colloidal mixture of organic and inorganic surds and ions. It serves as a matrix in which the nuclear protein complex known as chromatin is suspended. It also serves a storage place for enzyme material needed for DNA replication and synthesis of RNA.
During cell division chromatin material is stained as dark thread-like structure known as chromosomes. Under the compound microscope, the chromosomes appear to be made up of arms and centromere. Centromere is the place on which the chromosome where the spindle fibres are attached during the cell division each chromosome consists of two identical chromatids held together by a joint known as centromere which contain kinetochore proteins.
A chromosome is composed of DNA and protein all the information necessary to control the cell activities is located on the chromosome in the form of Jin which are transferred from one generation to another. The number of chromosome in all individuals of the same species remains constant generation after generation. The full number of chromosomes in the normal body cell is diploid where is haploid is the half number of chromosomes present in the germ are gamete cell. For human sperm and egg contain 23 chromosome each and that of drosophila contain 4 chromosome each in sperm and egg. So this week after fertilization the number of chromosomes remains constant in the next generation.