If a living being's body is a machine, then the brain is the processing unit or the control center of this machine. We know that the smallest unit of life is the cell, which has to be a machine as well. So, what is the processing unit of the cell? The control center of a cell is the nucleus, also known as kernel of the cell. Let us see the nucleus function and structure, and understand the working of nature's smallest processing unit.
All the genetic contents of the cell are enclosed in the nucleus, organized as multiple long chains of linear Deoxyribonucleic acid (DNA) molecules along with many kind of proteins, like histones, which form chromosomes. Within these chromosomes, there are genes enclosed, which are nothing but the cell's nuclear genome. In brief, nucleus function can be stated as to preserve the integrity of these genes and to preside over the activities in the cell by regulating gene processing or functionality.
Nucleus Function and Description
We will first understand the structure of a cell, and the nucleus in particular, then we can proceed to understand the nucleus functions. A nucleus is generally present only in all eukaryotic (membrane bound) cells. Most cells have just one nucleus and are called uninucleate, while some can have two or even more nuclei and such cells are known as binucleate and multinucleate respectively. However, there exists some matured cells where nucleus may be completely absent, such cells are called enucleate. The Red Blood Cells (RBC) in mammals and the sieve tube cells in plants are enucleate.
There's no fixed shape to the nucleus. Although, in most cases, they're round or elliptical; oval shaped or disc like nucleus have also been observed. Nucleus is enveloped by a double layered membrane, known as the nuclear membrane. A clear fluid called nucleoplasm or karyolymph is enclosed in the membrane. There is a network of fine thread-like matter, called chromatin network, which contains the DNA molecules and histones arranged in a particular manner. At the time of cell division, condensation of chromatin takes place in the nucleus, resulting in formation of distinct structures called chromosomes. Inside the nucleus, there also exists a round spherical body called nucleolus, amidst the chromatin mesh, and it has Ribonucleic Acid (RNA) and ribosomes in abundance, which is involved in protein synthesis. In plants, nucleus also controls the process of photosynthesis which is the main nucleus function in plant cells.
Now, with a clear structure in mind, let us take a glance at all the functions of the nucleus:
• Nucleus stores the genetic entropy necessary for reproduction, growth and metabolism of not only the cell it controls, but also of the organism on the whole. It controls the transfer and replication of hereditary molecules (DNA and RNA) between the parent cell and the child cell. Nucleus ensures equal distribution and exact copying of the genetic content during the process of cell replication. This is the main nucleus function in animal cells.
• The nucleus sustains and controls the cell growth by orchestrating the synthesis of structural proteins in the cell.
• Nucleus is the place for DNA transcription in which messenger RNA (mRNA) are produced which synthesize protein. The nucleus contains various types of proteins which can either directly control transcription or are indirectly involved in regulating the process.
• The process of energy and nutrient metabolism in the cell is regulated by the nucleus, by directing the synthesis and functioning of enzymes, which is a type of protein.
• The selective diffusion of cell's regulatory and energy molecules through the pores in the nuclear membrane is presided by the nucleus.
• Nucleus is responsible for the secretion of ribosomes. The ribosomes, in turn gets the credit for synthesizing all types of proteins.
So we can conclude that the cell nucleus stores all the chromosomal DNA of an organism, upon which the entire behavior and appearance of the organism depends. It is also responsible for the growth patterns of the body and controls correct replication of cells, which leads to the growth of that species. Looking at how vital the nucleus functions are, it can be understood why it is referred to as the control center of the cell.