Every eukaryotic cell has two main parts, the nucleus and the cytoplasm. The nucleus guides the life processes of the cell by issuing three types ofinstructions. First, the nucleus directs cellular reproduction, where a cell divides into two new cells. Second, the nucleus controls a cell's differentiation during the development of the organism. Third, the nucleus,regulates the metabolic activities of the cell. The nucleus is the largest, most prominent structure within a cell and its presence within a cell distinguishes the cell as being eukaryotic, meaning "possessing a true nucleus," versus being prokaryotic, meaning "lacking a true nucleus."Whereas eukaryotic nuclear materials are bounded by a membrane, called thenuclear membrane, prokaryotic nuclear materials are not.
The nucleus is the brain of the cell. It contains the DNA and RNA of thecell, which work together to build and control the cell. It produces proteins, which are carried by the endoplasmic reticulum to the various parts of the cell. These protiens are messages which give the cell orders. Like the mitochondria and organelles, the nucleus' protiens and DNA direct the rest of the cell.The membrane surrounding the nucleus is called the nuclear [Nucleus: detail] membrane. The "stuff" inside of the nucleus (besides the nucleolus) is called the nucleoplasm. Inside of the nucleus is is a round shape called the nucleoulus. Made up of protiens and RNA, the nucleolus helps in the formation of ribosomes.
One of the major components of the nucleus is the chromatin. This is where the genetic information of the cell is encoded. It is apparent through both light, and electron scanning, microscopes as a diffuse mass. As a cell begins to divide, this chromatin condenses. It becomes thick enough to be discenerned as separate structures. These structures are called chromosomes.
Chromosomes are an assembly of DNA and proteins which have functions in addition to the expression of genes. They are part of the machinery by which the cell ensures that its genetic information is both copied and delivered accurately to the daughter cells at cell division. Failures in this process can lead to aneuploidy (an abnormal chromosome number in the nucleus of a cell) which is probably the largest single cause of genetic disease in the new-born.
We understand the processes by which DNA replication is controlled in some detail but we have a poorer understanding of the chromosomal components involved in generating the functions necessary for a metaphase chromosome. Conceptually these components are defined - telomeres for protection of the chromosome ends, origins of DNA replication and centromeres which control the partition of the replicated chromosomes to the daughter cells.
The nucleus controls protein synthesis in the cytoplasm, by sending out moklecular messengers in the form of ribonucleic acids. These are called mRNA. They are synthesized in accordance to the DNA found along the chromatin material of the nucleus. The mRNA then conveys the genetic code to teh cytoplasm via nuclear pores. Once it reaches the cytoplasm, the mRNA attaches to ribosomes. This is where the genetic message is translated into the primary structure of a specific protein.
The ribosome, where this translation occurs, is also manufactured within the nucleus. It is made inside the organelle called the nucleolus. The nucleolus is the largest non-dividing part of the nucleus. It will be covered to a greater extent by a later presentation.