Hello, guys. In today’s article, we will study the Nucleus. What is a nucleus? Why is it called the control center of the cell? We will know the answers to many such questions today, so let’s start.
Why is the nucleus called the control center of the cell? and
What is the nucleus?
The nucleus is described as the ‘control room‘ of the cell. It directs and controls all cellular activities. It was discovered by Robert Brown in 1931. During the life span of a cell, the nucleus exists in two phases.
- The Interphase or Metabolic phaseÂ
- Division phase
In this article, we will study the Interphase or Metabolic phase.
Who discovered the nucleus?
The nucleus was discovered by Robert Brown in 1931.
What is the shape and size of the Nucleus?
The interphase nucleus, also known as the metabolic nucleus, controls the cell’s metabolic activities. It may be spherical, rounded, spheroidal, cylindrical, prismatic, branched, or lobed.
The size of the nucleus is different in the cells of other organisms, in various cells of an organism, and even in various stages in the same cell. The size is also related to the number of chromosomes.
What is the nucleo-cytoplasmic ratio?
There is a definite proportion in the size of the nucleus and the amount of cytoplasm. This can be represented by the nucleocytoplasmic index (NP).
NP = Vn/Vc – Vn
Where Vn = Volume of the nucleus
Vc = Volume of cytoplasm
Nuclear components of cell –
The interphase nucleus can be separated into the following parts.
- Nuclear envelopeÂ
- Nucleoplasm or ground substance
- Nuclear reticulum or chromatin net
- Nucleolus
- Chromocentres
What is the nuclear envelope or karyotheca?
The nuclear envelope is a double membranous sheath. It separates the nuclear material from the cytoplasm. It acts as a dynamic gateway between the nucleus and cytoplasm and regulates nucleocytoplasmic interaction.
Nuclear membranes –
A perinuclear space separates the two nuclear membranes of the nuclear envelope. This space is 20 nm in width. The nuclear membranes are 7-8 nm thick. The outer membrane has attached ribosomes. In places, it is continuous with the membranes of the ER. The atomic surface of the inner membrane is coated with filaments and fibers. These form a fibrous lamina or nuclear cortex.
What are nuclear pores?Â
Pores perforate the nuclear envelope. The outer and inner nuclear membranes are continuous at the margin of these pores.
The nuclear pores are 100 nm wide circular channels. Some electron-dense material occludes these. This projects outward in the cytoplasm and inward into the nucleoplasm. These structures are called annuli. The two together form a pore complex.
Each pore complex has an outer diameter of 90 nm, an Inner diameter of 25 nm, and a wall thickness of 30 nm. The electron-dense material consists of fibrous and particulate structures. These are present along the margin of the nuclear pore and form an annulus.
What is annulus?
The annulus appears as a ring or cylinder of electron-dense material of nuclear pore. It is formed of two sets of eight evenly spaced annular granules. And a central granule. One set is arranged on the outer surface, and the other set is on the inner surface of the annulus.
The granules may be formed of compact material or fibrillar material. Fine fibers extend from the central annule to peripheral annular granules. Annuli around the pores regulate the exchange of macromolecules about their size.
Fibrous or Nuclear laminar –
The inner surface of the nuclear envelope is plastered with a fibrous coating called nuclear cortex. Its fibers are proteinaceous and similar to actin polymers. The fibers form funnel-shaped whorls. These funnels communicate with the nuclear pores, and the direct material cortex functions as a funnel to come out of the nucleus.
The nuclear cortex functions as a funnel to direct materials toward pore channels. It also provides a supporting lamella.
What is the function of the nuclear envelope?
- The nuclear envelope separates the genetic components of the cell (Chromosomes) from the protein synthesis machinery.
- Nuclear pores serve for the transfer of macromolecules.
- The nuclear envelope provides a surface for the attachment of structural elements of cytoplasm, such as myofilament, microtubules, and microfilaments.Â
- Interphase chromatin remains attached to the inner nuclear membrane.
- The nuclear envelope gives rise to membranes of ER and Golgi and participates in membrane flow.
- The nuclear envelope carries electron transport system enzymes similar to endoplasmic reticulum enzymes.
What is nucleoplasm? Or What is nuclear sap?
It is a transparent ground substance. The Chromatin network remains suspended in it. It is a mixture of proteins, large amounts of phosphorus, and some nucleic acids (RNA). Several hydrolytic enzymes, such as ribonuclease, alkaline phostophosphatase, and dipeptidase, are also found in the nucleoplasm.
What is the function of the nucleoplasm?
- Nucleoplasm is associated with the processing of newly synthesized RNA and its transport from the nucleus to the cytoplasm.
- Nucleoplasm acts as a skeleton of the nucleus and maintains the nucleus.
- It contains enzymes and proteins needed to replicate DNA and synthesize RNA and ribosomes.
What is the nucleolus?
Nuclear Reticulum or Chromatin Net –
Embedded in the nuclear sap is the network of twisted filaments or threads known as chromonemata, and their network is called the atomic reticulum or chromatin net. It contracts and organizes into a distinct chromosome during cell division.
Euchromatin and heterochromatin –
The cell chromatin can be differentiated into two types. The fine thread-like linen of the chromatin, which stains lightly with basic dyes, is called euchromatin. At certain regions, the chromatin is condensed and darkly stained. This is known as heterochromatin.
The heterochromatin regions can be seen in the interphase and prophase. It does not unravel in telophase like the remaining euchromatin.
The euchromatin also exhibits different affinities to the dyes. The linen of the chromatin, in the form of lightly stained threads, is composed of chromatin (Stains with acidic dyes), and the darkly stained granules (chromomeres) present on the linen are formed of basic rotation or chromatin proper.
In some cases, the most significant regions of the nucleus take dark stains with basic fuchsin. These are known as chromocentres of karyosomes.
Unique sex chromatin bodies or bare bodies are found in the periphery of the nucleus. These are more common in mammalian cells, especially in females. Their number usually depends upon the number of sets of X -chromosomes. Usually, there is one sex chromatin body for a diploid set of chromosomes.
What is chromocenter?
In the interphase nucleus of specific cells, some areas of considerable size take darker stains than the rest of the chromatin. These darkly stained areas are heterochromatic regions of the chromosomes that are prone to premature condensation.
There can be only one or many heterochromatic regions of several or all the nucleus chromosomes. The chromocenter is well-marked in the nuclei of salivary gland cells of Drosophila.
What is the function of the nucleus?
The nucleus is the controlling center of the cell. It controls all the cell’s metabolic activities by regulating the synthesis of enzymes required therein. The nucleus controls the inheritance of characters from parents to offspring. It is responsible for the development of characters.
What we are and how we look are determined by genes inherited from our parents. These genes are present in the chromosomes of the nucleus. Several experiments conducted by scientists illustrate the role of the nucleus.
Hammer Ling’s Experiment to demonstrate the Importance of nucleus –
A German biologist. J. Hammerling 1934 demonstrated that the nucleus controls the functioning of cells and, ultimately, the characters of the individuals by conducting experiments on Acetabularia, a green alga. Two species of Acetabularia, A. crenulata, and A. mediterranea, differ in the shape of their caps.In A. crenulata, the cap is digitateddigitated having loose rays, whereas in A. Mediterranean Mediterranean, the cap is umbrella-like. In both species, the nucleus lies at the bottom of the stalk in the rhizoid. Acetabularia possesses the power of regeneration. If its cap is cut off, it is regenerated again. However, after removing the caps, the stalk of one species is grafted on the rhizoid of the other (note that rhizoid).
As the carrier of the nucleus) The shape of the cap on the grafted Acetabularia is determined by the nucleus in the rhizoid (not by the rhizoid). If the nucleus belongs to A. crenulata, the cap is digitate or crenulate type, and if it belongs to A. mediterranea, the cap developed is mediterranean type. When both nuclei are present, the shape of the cap is found to be intermediate.
This indicates that the nucleus controls the characteristics of an individual.
What is the nucleolar cycle?
The nucleolus, as an organized body, lacks continuity. During mitosis, it undergoes cyclic changes. It disappears at the beginning of cell division (prophase, and is formed again at the end of cell division in telophase.
The nucleolus is formed at a definite region by one or more chromosomes of a haploid set. Such chromosomes are known as nucleolar chromosomes. Most diploid species possess two nucleolar chromosomes in each diploid or somatic cell.
But in man, chromosomes numbering 13, 14, 15, 21, and 22 participate in nucleolus formation. The specific region of these chromosomes active in nucleolar formation is known as the nucleolar organizer zone or nucleolar zone. Very often, but not always, it is marked by secondary constriction. The nucleolar organizer carries genes for 18S and 28S ribosomal RNA.
During prophase, the amorphous part of the nucleolus disappears, and the chromatin loop is withdrawn into the nucleolar organizer region of the corresponding chromosome. During telophase, the nucleolus is reorganized in the following two steps.
- The convoluted chromatin loop uncoils from the nucleolar organizer and gets surrounded by fibrillar and granular material. These are produced from the chromocentre of the interphase nucleus.
- The nucleolus matrix and its essential proteins and RNA (the nucleolar substances) are produced within the chromocenter and are liberated in small perinucleolar bodies. These fuse to form the mature interphase nucleolus.
What are nucleoproteins?
Nucleoproteins are the major and the most critical component of the nucleus. These are compounds of nucleic acids and proteins. The proteins present in the nucleus’s proteins are specific categories.
- Basic proteins
- Nonhistone acid proteins.
What are essential proteins?
These are low molecular weight proteins having a molecular weight ranging from 1000 to 12000. These are basic. The amount of essential proteins is proportional to the amount of DNA with which they are intimately associated.
The chief essential proteins found in the nucleus are protamines and histones. The histones are more widely distributed and are composed of lysine and arginine. These are about 55% of the total chromatin material. The protamines are restricted in their distribution and are found mainly in fish spermatozoa. These are rich in arginine.
What are nonhistone or acid proteins?
Nonhistone proteins are acidic and usually equated with the residual proteins of the chromosomes. They contain tryptophan and tyrosine. Nonhistone proteins differ from histones because they contain a higher concentration of tryptophan.
Their amount chiefly depends upon the physiological activity of the cell. The nonhistone or residual proteins are said to perform the special metabolic functions of the nucleus.
The nucleoproteins in the chromatin material or the chromosomes serve as a framework to which the different nucleic acids are attached. In addition, nucleohistones are concerned with the maintenance and reproduction of chromosomes, and nucleononhistones are concerned with the special metabolic function of the nucleus.
What is euchromatin and heterochromatin?
What is heteropyknosis?
Heteropyknosis (Gr. Differential staining) is the property of specific chromosomes or their parts to remain condensed and stain more intensely than other chromosomes or their parts during the nuclear cycle.
Conclusion –
So, friends, in today’s article, we studied why the nucleus is called the cell’s control center. Friends, if you like this article, please comment, share, and tell us your suggestions and our mistakes.
Thank you so much
