Introduction
As we all know a cell is a structural unit of organisms. Each cell carries all the biological functions like respiration, nutrition, excretion, reproduction, growth, etc. That is why cells are also called functional units of the organisms. Different plant and animal cells have different structures and components. Each living cell is made up of a single-membrane protoplasm. The protoplasm is composed of two parts called the nucleus and the cytoplasm. The nucleus is the main part of a cell. Below is some information about the nucleus structure and function (3) & (4).
Definition
The double membrane part in the protoplasm of the eukaryotic cell that contains the protoplasmic juice and chromatin lattice also regulates all the biological processes of the cell, called the nucleus. The nucleus is the densest, membranous, and almost spherical part of the protoplasm. The nucleus is the life of a cell. In 1831, Robert Brown first discovered and named the nucleus in an orchid leaf cell (5) & (6).
Location
The nucleus is found in the protoplasm of all types of eukaryotic cells. The nucleus is located near the cell wall of plant cells and usually in the center of the cell in animal cells. Prokaryotic cells do not have a well-formed nucleus. In a mature plant cell, the nucleus is on one side when the vacuole is large (Agarwal & Agarwal).
Facts about Nucleus
There are some facts about the nucleus.
1. The shape of the nucleus is round, oval, cylindrical, elliptical, spiral-shaped, disc-shaped, crown-shaped, radish-shaped, or branched.
2. Each cell usually has a nucleus.
3. The prokaryotic cell does not have a well-formed nucleus.
4. A number of cells, such as SIV cells, human blood cells, etc. do not have a nucleus.
5. Some algae and fungi cells have a large number of nuclei, such as Vaucheria, Mucor, Botrydium, etc.
6. The size of the nucleus can vary in different cells. Its diameter is usually one micrometer or less.
7. The nucleus occupies 10- 15% of the volume of a cell.
8. The number of chromosomes in the nucleus of a human body cell is 46.
9. The size of the nucleus is relatively large in mature cells and in the cells of the growing part (1) & (7).
Structure of the nucleus
The four main parts of the nucleus are found at the interface stage before the cell division begins. These four parts are the nuclear membrane, the nucleoplasm, the nucleolus, and the nuclear reticulum, or chromatin fiber (Agarwal & Agarwal).
1. Nuclear membrane
The two-layered membranes that surround the nucleus are called the nuclear membrane. This membrane is made up of proteins and lipids. The layer adjacent to the cytoplasm of the nuclear membrane is called the outer membrane and the layer adjacent to the nucleoplasm is called the inner membrane.
The nuclear membrane has a number of holes called nuclear holes. The space between the two layers of the membrane is called the perinuclear cisternae. This part connects the nucleoplasm to the cytoplasm.
Properties
1. A nuclear membrane is a living and transparent membrane.
2. This membrane covers the nucleus and separates the nucleus from the cytoplasm.
3. The nuclear membrane has two layers. Each layer is about 80Å thick and the thickness between the two layers is about 100 to 150Å.
4. The upper layer of the nuclear membrane has numerous holes. And the lower layer has no holes.
5. There are eight round and small particles located inside each nuclear hole. The presence of these particles can cause the pores to shrink and expand (6).
Function
The function of the nuclear membrane is to separate and store nuclear material from the cytoplasm. Nuclear pores located in the nuclear membrane protect the interaction with nucleoplasm and cytoplasm. This membrane attaches to the endoplasmic reticulum and strengthens the position of the nucleus (Agarwal & Agarwal) & (5).
2. Nucleoplasm
The nucleoplasm is a semi-liquid, transparent, and granular fluid located between the nuclear membrane and nucleolus called nucleus sap or karyolymph. Nucleoplasm is a more granular and dense jelly-type part than the cytoplasm. Chromatin fibers are floating in the nucleoplasm. It also contains DNA, RNA, phosphor-proteins, histones, enzymes, mineral salts, etc.
Function
The function of the nucleoplasm is to hold the chromatin lattice, to support the various biological functions of the nucleus, and to hold the nucleolus. The nucleoplasm stores food during cell division (6) & 7).
3. Nucleolus
The nucleolus is a small, dense spherical part located inside the nucleolus. Each nucleus usually has one nucleolus. The nucleolus consists of three parts such as fibrous, granular, and matrix. In 1781, the scientist Fontana first described the nucleolus, which consisted mainly of phosphor-proteins (80%) and RNA (15%). The nucleolus also contains some amount of DNA (5%). It contains numerous small granular, threaded, and irregular parts. The nucleolus is usually attached to a specific location on a specific chromosome called SAT or satellite. The nucleolus is not present in the nucleus of cells that do not normally synthesize proteins (1).
Function
1. The nucleolus acts as a reservoir of nucleic acids.
2. The function of nucleolus is to synthesize and store proteins.
3. The nucleolus plays a special role in the chromosomal movement.
4. The nucleolus located in the nucleus also synthesizes different types of RNA (Ribonucleic acid).
5. This part of the nucleus forms the ribosome (6).
4. Nuclear reticulum or chromatin fiber
The nucleoplasm consists of numerous long and spiral-threaded fibers made up of nucleic acids (DNA and RNA) and proteins called chromatin fibers. When chromatin fibers are scattered in the nucleoplasm and joined together to form a reticulum, it is called a nuclear reticulum. In 1879, scientist Fleming first discovered the nuclear reticulum. The nuclear reticulum consists of a combination of DNA and histone proteins. Chromatin fibers are formed in the interphase of cell division. The fibers are transformed into a rod-shaped structure in the prophase stage known as the chromosome. The part with more DNA in the nuclear reticulum is called euchromatin and the part with less DNA is called heterochromatin (Agarwal & Agarwal) & (7).
Function
1. The chromosomes located inside the nuclear reticulum contain and carry the characteristics of heredity.
2. Nuclear reticulum plays a major role in cell division.
3. This part of the nucleus also plays a significant role in mutations, variations, etc.
4. The nuclear reticulum or chromatin fiber assists in the transfer of protein through mRNA synthesis (1) & (3).
Role of the nucleus in heredity
Characteristics of the parents are passed on to the offspring is called heredity. The substances through which the traits of the parents are passed onto the offspring are called the heredity objects. The chromosome is located in the nucleus. Part of the DNA in the chromosome is the gene, which carries the parental traits directly to the offspring. Therefore, the genes in the DNA of the nucleus act as heredity objects. Genes contain different characteristics of an organism like body color, size, eye color, and variations which are passed from parents to offspring. This is because such functions are usually performed through the chromosome. These chromosomes are present in the nucleus. Therefore, it can be said that the nucleus is the main carrier and bearer of the heredity of the organism (3) & (6).
Chemical composition of the nucleus
The nucleus consists of nucleic acid (Deoxyribonucleic acid and Ribonucleic acid), proteins (nucleo-protein, nucleo-histone, non-histone, nuclear enzyme, etc.), and various mineral salts such as phosphorus, potassium, sodium, calcium, magnesium. The enzymes found in the nucleus are Diphosphopyridine nucleotide, nucleoside phosphorylase, nucleotide triphosphates, adenosine deaminase, guanase, pyruvate kinase, ribonuclease, etc. Of all these enzymes, the Diphosphopyridine nucleotide acts as a coenzyme for protein synthesis. The nucleus also contains some amount of plain water, lipids, protamine-type proteins, some cofactors, acetyl-CoA, and other elements (Agarwal & Agarwal) & (3).
Why is the nucleus called the brain of the cell?
The nucleus is the most visible substance in the cytoplasm of a cell that has a specific membrane, carrying chromosomes. It controls all the activities of the cell, just as the human brain controls all the activities of the human body. The nucleus controls all activities, including metabolic functions in the cell, regulates the heredity of the organism through chromosomes, and actively participates in meiosis and mitosis. That is why the nucleus is called the “brain of the cell” (Agarwal & Agarwal).
Nucleus structure and function
The nucleus controls all the functions of the cell.
1. The nucleus acts as a reservoir of nucleic acids.
2. DNA of chromatin located in the nucleus controls all metabolic functions of the cell.
3. The RNA produced by the nucleus binds to the ribosomal proteins formed in the cytoplasm and produces ribosomes.
4. It helps in cell division.
5. Proteins and RNA synthesis in cells occur in the nucleus.
6. The nucleus plays an active role in the formation of chromosomes during cell division.
7. The nucleus controls all the biological activities of the cell.
8. The bearer and carrier of the genetic trait of an organism is the chromosome or chromatin, which is located in the nucleus.
9. The role of the nucleus in mutation, variation, etc. is very important.
10. The nucleus contains chromosomes. These chromosomes participate in DNA synthesis (6) & (7).
