The nucleus is essential to the functioning of every cell because it controls virtually every cellular process. The presence or absence of a nucleus within a cell is the primary criterion for classifying the type of cell (categorized either as a prokaryotic or eukaryotic cell). Lets learn more about structure and function of nucleus in eukaryotes.
What is the Nucleus?
The nucleus, which has the shape of a sphere, is an organelle found in every type of eukaryotic cell. A eukaryotic cell’s nucleus is its central hub. Gene regulation, expression and regulation are also under its domain. Nucleus components include the nuclear membrane, chromosomes, nucleoplasm, and nucleolus. Comparatively, the nucleus occupies just around 10% of the total volume of the cell, making it the most noticeable organelle.
In most cases, the nucleus is the primary organelle in a eukaryotic cell. However, some eukaryotic cells, including red blood cells, are enucleate (nucleus-free). Some, like slime mould, have several nuclei, or are multinucleate. A nuclear membrane separates the nucleus from the rest of the cell, or cytoplasm. The first organelle to be found or found out about was the nucleus. Antonie van Leeuwenhoek notices a “lumen” in the nucleus of salmon red blood cells. Unlike the red blood cells of mammals, the red blood cells of other vertebrates still have nuclei.
Structure of the Nucleus
Figure 1: Labelled Diagram of Nucleus explains structure and function of nucleus in eukaryotes.
The nucleus of a cell is made up of chromosomes, nucleoplasm, the nucleolus, and the nuclear envelope (Figure 1). The matrix inside the nucleus is called nucleoplasm or karyoplasm. The cytoplasm and the parts of the nucleus are separated by the nuclear membrane. The nuclear envelope is made up of phospholipids that form a lipid bilayer, just like the cell membrane.
The envelope helps the nucleus keep its shape and helps control how molecules move in and out of the nucleus through nuclear pores. DNA is in the nucleus of the cell. The DNA tells the cell how to look, work, and grow. The nucleus is like the brain in that it coordinates all the other parts of the cell. Here, we’ll talk about the main parts of the nuclear structure.
a. Nuclear Membrane
The components of the nucleus are enclosed by a double-layered membrane. The endoplasmic reticulum and the outer membrane are fused into a single structure. The nuclear envelope is connected with the endoplasmic reticulum in such a way that the internal compartment of the nuclear envelope continuous with the lumen of the endoplasmic reticulum.
Between the two layers of a nuclear membrane is a space called the perinuclear space, which is filled with liquid. The nucleus gets through the remaining of the cell or the cytoplasm through several openings called nuclear pores. Such nuclear pores are the sites for the exchange of large molecules between the nucleus and cytoplasm. The nuclear membrane is made up of lipoproteins, perinuclear space, pores, annuli material, an inner dense lamella.
Chromatin is a string of DNA and protein molecules that make up chromosomes. Based on what they do, heterochromatin and euchromatin are two more types of chromatin. Heterochromatin is a tightly packed, transcriptionally inactive form that is usually found close to the nuclear membrane. On the other hand, a transcribing cell has a lot of euchromatin, which is a milder, less dense form of chromatin.
During the process of cell division, the chromatin filaments that have been segregated from one another become thicker, more dense, and smaller, and are now referred to as chromosomes. It is essentially a nucleoprotein composed of nucleic acid and histone, a basic protein. Nucleic acid is a highly complex organic acid including sugar, nitrogenous bases, and phosphate.
DNA (Deoxyribonucleic acid) especially found in the cytoplasm in soluble form and is called soluble RNA. It is also present in some amounts in the ribosomes of nucleus, chromatin, and nucleolus. It is synthesized from DNA and is piled up in the nucleolus. It travels to the cytoplasm and gets attached to the ribosome.
c. Nuclear Sap
The clear, homogeneous, transparent, colloidal, and sometimes thick liquid is surrounded by the nuclear membrane. It is mostly made up of nucleoproteins and a small amount of inorganic and organic substances like nucleic acids, proteins with dissolved phosphorus, ribose sugars, minerals, enzymes, and nucleotides.
The nucleolus is a solid structure in the nucleus that looks like a sphere. Some eukaryotic organisms have nuclei that are made up of as many as four nucleoli. By making ribosomes, the nucleolus plays an indirect role in protein synthesis. These ribosomes are organelles in the cell that are made of RNA and proteins. They are moved to the cytoplasm and attached to the endoplasmic reticulum. The organelles in a cell that make proteins are called ribosomes. The nucleolus goes away when a cell divides, but it comes back when the cell division is done.
Characteristics of Nucleolus
The following is a brief overview of some of the more salient points. A nucleus may have anywhere from one to many nucleoli. In the later stages of prophase, the nucleolus is no longer present. Appears again in the telophase phase. It acts as a repository for RNA.
Figure 2: Structure and Function of Nucleus in Eukaryotes
Functions of the Cell Nucleus
The cell nucleus controls the traits that are passed down from generation to generation. This organelle is also in charge of making proteins, growing, dividing cells, and changing into different types of cells. The important job is done by the nucleus of a cell. Here are some of the most important things that the nucleus does.
Chromatin is referred to as the storage of hereditary material, the genes in the form of long and thin DNA strands. The Nucleolus is referred to as the storage of proteins and RNA in the nucleolus (Figure 2). The Nucleus is a site for transcription in which messenger RNA is produced for protein synthesis. The nucleus functions as the exchange of hereditary molecules that is RNA and DNA between the nucleus and the rest of the cell. During cell division, chromatins are arranged into chromosomes in the nucleus. It functions in the production of ribosomes in the nucleolus. The nucleus functions the selective transportation of regulatory factors and energy molecules through nuclear pores.
Distribution of Nucleus
On the basis of the cell’s presence or absence, several cell types are categorised. The many varieties are described below:
Uninucleate cell: Uninucleate cell also referred to as monokaryotic cells, mostly plant cells which contain a single nucleus.
Bi-nucleate cell: It is also called a dikaryotic cell. It contains two nuclei at a time. The examples are one paramecium (have mega and micronucleus), balantidium, and liver cells and cartilage cells.
Multinucleate cells: It is also known as the polynucleated cell which contains more than 2 nuclei at a time. For example, plants latex cells and latex vessels. In animals, striated muscle cells and bone marrow cells.
Enucleate cells: Cells without a nucleus are called enucleate cells. However, some living cells like mature sieve tubes of phloem and RBC’s of mature mammals lack nuclei.
FAQs on Structure and Function of Nucleus in Eukaryotes
The fundamental biological building block that may be traced from one generation to the next. The DNA sequences that make up genes are ordered sequentially on chromosomes in the nucleus of each cell.
Chromatin is referred to as the storage of genetic material, the DNA strands containing the genes.
RNA and proteins are stored in the nucleolus, which is referred to as the nucleolus.
The nucleus is the location of transcription, where messenger RNA for protein synthesis is created.
The nucleus is responsible for the exchange of RNA and DNA between the nucleus.