Let us draw an analogy at a grand scale of the entire human body. We, as animals or organisms, cannot function without our brain, can we? It is the command and control center of our whole body. Now, if we take this down to the cellular level, the same organizational arrangement can be found there too. In the individual cells of our body, we have a command and control center and several other organelles that work together to perform several vital functions. This command and control center of the cell is known as the Cell Nucleus. In this article on Cell Nucleus facts, we are going to learn about this important cell organelle in details. Our listicle and the factual article will span over the structure and functions of the Cell Nucleus. So, without further ado, let us begin.
Interesting Cell Nucleus Facts: 1-5 | What is Cell Nucleus?
1. Cell Nucleus is a cell organelle. Yes, it is just a small cellular organ that is found inside a cell. It is found only in Eukaryotic cells.
2. Just like a brain, the Cell Nucleus is considered to be the brain of a cell. This brings us to a vital conclusion straight away. There is only one Cell Nucleus in a single cell.
3. Well, it is true. Every cell has a single nucleus. But there are a few exceptions. For example, the matured red blood cells found in the human body do not have any nucleus at all.
4. Paramecium (which is a single-celled organism found in freshwater) is known to have two Cell Nuclei (singular is the nucleus; the plural is nuclei). Slime mold, on the other hand, can have millions of nuclei.
5. Those Eukaryotic cells that do not have any nuclei are referred to as enucleate. Those that have two or more nuclei are known as multinucleate.
Interesting Cell Nucleus Facts: 6-10 | Discovery of Cell Nucleus
6. Cell Nucleus was originally identified by the Father of Microbiology – Antoine Philips van Leeuwenhoek. Sadly though, Antoine is not really credited for the discovery of this important cell organelle.
7. Antoine Philips van Leeuwenhoek (1632 to 1723) was once studying the red blood cells of a salmon. That is when he found the ‘lumen’ or the nucleus. It must be noted that red blood cells of mammals do not have nucleus but other vertebrates do have a nucleus in their red blood cells.
8. Then came Franz Bauer. In 1804, this person came up with a description of the Cell Nucleus. However, the description was not a detailed one.
9. The credit for the discovery of the Cell Nucleus is given to a botanist from Scotland. His name was Robert Brown. In 1831, he gave a highly detailed description of the Cell Nucleus while talking at Linnean Society of London.
10. Robert Brown spotted an opaque area in the cells while studying orchids using a microscope. He called the opaque area as ‘areola’ or ‘nucleus.’ He spotted the areola in the cells found in the outer layer of the flower.
Interesting Cell Nucleus Facts: 11-15 | A Bit of Fighting Over Cell Nucleus
11. Robert Brown only described the Cell Nucleus. He didn’t provide any potential function that the Cell Nucleus may play in a cell. Matthias Schleiden in 1838 came up with the proposal that Cell Nucleus plays a very important role in cell generation.
12. It was Matthias Schleiden who introduced the name Cytoblast (which means Cell Builder). The reason why came up with such a proposal was that he saw new cells getting assembled around the Cytoblasts.
13. This didn’t resonate well with Franz Meyen, and he vehemently opposed the view presented by Matthias Schleiden. The reason why Meyen opposed Schleiden was that Meyen had already proposed a theory in which said that cells multiply by division. Meyen also said that many cells would simply have no nuclei in them.
14. Schleiden’s proposal that cells were generated from the beginning by Cytoblasts. This is proposal given by Schleiden directly contradicted all the work that Rudolf Virchow (1855) and Robert Remark (1852) did.
15. The two people – Virchow and Remark – said and of course, propagated that cells were generated only by cells. However, Virchow and Remark never clarified anything about the function of the nucleus.
Interesting Cell Nucleus Facts: 16-20 | A Bit of Fighting Over Cell Nucleus
16. Oscar Hertwig published various studies somewhere between 1877 and 1878. He was studying sea urchin eggs’ fertilization. In his studies, he revealed that sperm’s nucleus entered oocyte (a female germ cell involved in reproduction) and ended up fusing with the nucleus of the sperm.
17. This finding of Oscar Hertwig was the reason why for the first time it was suggested that individuals develop from a nucleated cell. Hertwig’s finding was totally against the theory given by Ernst Haeckel where it was proposed that a species’ complete phylogeny is repeated during the development of the embryo.
18. According to Haeckel’s theory, even the first nucleated cell is generated during the embryonic development and that it happens from a structureless mass of a primordial mucus. This structureless mass was known as Monerula while the primordial mucus was known as Urschleim.
19. Because of this disagreement between Hertwig’s theory and Haeckel’s theory, scientists of that period had quite a long discussion over the necessity of the sperm cell for fertilization of the egg. This resulted in Hertwig searching for further proofs and ended up confirming his findings in other groups of animals like mollusks and amphibians.
20. Hertwig’s findings were further confirmed in 1884 by Eduard Strasburger. As a result of this, it was unanimously accepted that nucleus played a major role in heredity. August Weismann took it even further in 1873 when he proposed that germ cells from both parents play an equal role in heredity.
In later years Mitosis was discovered along with rediscovery of Mendelian rules towards early 20th century. It was only after this that the Chromosome Theory of heredity was eventually developed.
In case you are wondering what Mendelian rules are, here is what you need to know for now (as we will be discussing Mendelian rules sometime later): Gregor Mendel gave a theory of biological inheritance in years 1865 and 1866. The laws were initially discarded but later in the early 20th century, Mendel’s laws were integrated with Boveri–Sutton chromosome theory. This integration was made by Thomas Hunt Morgan in the year 1915. The combination of the two eventually became the core of Classical Genetics and Gregor Mendel is today considered as the founder of modern genetics.
Interesting Cell Nucleus Facts: 21-25 | Position and Size of Cell Nucleus
21. The Cell Nucleus is a very specialized cell organelle, and in animal cells, it is the largest cell organelle. In plant cells, the largest cell organelle is the vacuole and not the Cell Nucleus.
22. In cells of the mammals, the nucleus is as big as 6 micrometers (µm) in diameter. So, in mammalian cells, the nucleus alone occupies around 10% of the entire volume of the cell.
23. The size of the Cell Nucleus can vary from one organism to another. Also, its size is dependent on the stage of the cell cycle. So, not every organism (plants or animals) will have a Cell Nucleus measuring 6 µm in diameter.
24. In animal cells, the Cell Nucleus is located more or less towards the center of the cell. However, this is not the case during cell reproduction or cell division. During cell division, the nucleus sits in an off-center position.
25. In plant cells, the Cell Nucleus is more or less towards the border of the cell. This happens because the large vacuole occupies the near-central position.
Interesting Cell Nucleus Facts: 26-90 | Structure of Cell Nucleus
26. The Cell Nucleus is roughly spherical. However, that may not necessarily be the case. The Cell Nucleus may also have an irregular shape.
27. The Cell Nucleus has different parts. They are:
- Nuclear Envelope (which is further divided into):
- Outer Membrane.
- Inner Membrane.
- Nuclear Pores.
- Nuclear Lamina.
- Nucleolus (present inside the nucleus).
- Nucleoplasm (sometimes known as Karyolymph), which has a composition similar to the cytosol, which is present outside the Cell Nucleus.
- Chromatin (which is further divided into):
Cell Nucleus Facts | Nuclear Envelope
28. THE NUCLEAR ENVELOPE: This is also known as the Nuclear Membrane. It is composed of two layers of cellular membranes. The inner layer is known as the Inner Membrane while the outer layer is known as the Outer Membrane.
29. There is a space between the Inner Membrane and the Outer Membrane. This space between the two layers of membranes is known as the Perinuclear Space.
30. So essentially, the Inner Membrane and the Outer Membrane are arranged parallelly. The space or distance between them is 10 nm to 50 nm (nm stands for nanometers and is equal to 1 x 10-9 meters).
32. It is interesting to note that the perinuclear space is continuous with the lumen of the Rough Endoplasmic Reticulum.
33. The job of the Nuclear Envelope or Nuclear Membrane is to enclose the entire nucleus and, in the process, separate the genetic material of the cell (present inside the nucleus) from the cytoplasm or cytosol that surrounds the nucleus.
34. The Nuclear Membrane also has small pores or holes that are known as the Nuclear Pores. The whole purpose of these pores is to provide an aqueous channel right through the Nuclear Envelope.
35. The inner surface of the Nuclear Envelope, that is, the inner face of the Inner Membrane (that is, the side of the Inner Membrane that faces the Nucleoplasm) has a lining of what is known as Nuclear Lamina.
Cell Nucleus Facts | Nuclear Pores
37. The molecular weight of these pores is around 125 million daltons. In vertebrates, there are several hundred proteins that make up a single Nuclear Pore. In yeasts, around 50 proteins make up a single pore.
38. The diameter of the Nuclear Pores is around 100 nm. It is however interesting to note that the gap in the pores through which particles diffuse in and out of the Cell Nucleus is just 9 nm wide. The reason for this is that these pores have regulatory systems right at their center.
39. Because the gap is just 9 nm wide, not every molecule can diffuse in and out of the Cell Nucleus. Only small molecules that are water-soluble can diffuse while those that are big molecules such as large proteins and nucleic acids etc. fail to move in and out of the Cell Nucleus through the Nuclear Pores.
40. Around 3,000 to 4,000 Nuclear Pores are present on the Nuclear Envelope of a typical mammalian cell’s Cell Nucleus. Each of these Nuclear Pores has an eightfold-symmetric structure of the shape of a ring. These structures are located where the Outer Membrane and Inner Membrane of the Nuclear Envelope fuse.
41. This ring-like structure has yet another structure attached to it. This other structure is known as the Nuclear Basket. The Nuclear Basket extends all the way into the Nucleoplasm.
42. The ring-like structures also have some filamentous extensions that reach directly into the Cytoplasm surrounding the Cell Nucleus.
43. Both the Nuclear Basket and the filamentous extensions have one common function. That function is none other than mediating binding of what we know as nuclear transport proteins.
Cell Nucleus Facts | Nuclear Lamina
44. THE NUCLEAR LAMINA: When we say Nuclear Lamina, we say it about animal cells. However, Nuclear Lamina has also been found in plant cells but with very different composition. A new term was proposed for Nuclear Lamina in plants. The term was Plamina. The term is however not widely used because Nuclear Lamina in plants has structural similarities with that of Nuclear Lamina of animal cells. There are compositional differences between the two. Source
45. What is Nuclear Lamina? To simplify things for you, we will restrict our discussion to animal cells only. Well, Nuclear Lamina is a wire mesh-like structure that is responsible for providing mechanical support to the Cell Nucleus.
46. The Nuclear Lamina is found on the Nuclear Envelope’s internal face. Putting it in layman terms, it is found on the face of the Inner Membrane that faces the Nucleoplasm.
47. While the primary function of the Nuclear Lamina is to provide structural support to the Nuclear Membrane, it also works as an anchoring site for the Chromosomes.
48. Lamin proteins are the primary components that make up the Nuclear Lamina. Cytoplasm is the site for the synthesis of Lamin proteins. Once synthesized, these proteins are then transported to the interior of the Cell Nucleus.
49. Once inside the Cell Nucleus, the Lamin proteins are assembled and then added to the existing Nuclear Lamina network.
50. Here is something interesting to note. The Lamin proteins are also found on the Cytoplasmic face of the Nuclear Membrane. That is, it is also found on the face of the Outer Membrane that faces the Cytoplasm.
51. Lamin proteins such as Nesprin and Emerin that are found on the Cytoplasmic face of the Nuclear Membrane are also known for providing mechanical support to the Nuclear Membrane.
52. Lamin proteins found on the Cytoplasmic face of the Nuclear Envelope also work as anchoring sites for Nuclear Pores.
Cell Nucleus Facts | Nucleolus53. THE NUCLEOLUS: The Nucleolus is present inside the Cell Nucleus. Sometimes referred to as suborganelle, it is not bounded by any membrane.
54. It is known as Ribosomal factory. What are Ribosomes? Ribosomes are those structures within the cells that are responsible for producing proteins. So basically, Nucleolus is where the Ribosomes are manufactured.
55. It is quite easy to recognize this substructure that can be found in the Cell Nucleus of the Eukaryotic Cells. Phase Contrast Microscopy is one of the several methods that is used for identifying this suborganelle. Using a variety of dyes is yet another method.
56. Found both in animal and plant cells, the Nucleolus is also an important place where Ribosomal RNA synthesis takes place.
57. The number of Nucleoli (plural for Nucleolus) present in the Cell Nucleus can vary from organism to organism. Some animals and plants have more than one Nucleolus in the Cell Nucleus.
58. The nucleolus is just one of the several structures that are found inside the Cell Nucleus. This suborganelle is formed around tandem repeats of rDNA. rDNA is the DNA coding for rRNA or Ribosomal RNA. These regions of tandem repeats or rDNA are called NORs or Nucleolus Organizer Regions.
59. NOR is a chromosomal region in a cell. However, this chromosomal region is a specific part of chromosomes that contain the Ribosomal DNA or rDNA coding that is repeated again and again (tandem repeats of rDNA).
60. The Nucleolus Organizer Region contains the genes for pre-rRNA. The NOR is the foundation of the Nucleolus.
61. The Nucleolus is the largest structure that is found inside the Cell Nucleus. It is located near the center (not exactly at the center) of the Cell Nucleus.
62. Three things make up a Nucleolus – RNA (Ribonucleic Acid), DNA (Deoxyribonucleic Acid) and various proteins.
63. As far as the structure of the Nucleolus is concerned, it has three parts or components (in higher Eukaryotes):
- DFC or Dense Fibrillar Component
- FC or Fibrillar Center
- GC or Granular Component
64. FC or Fibrillar Center forms the innermost region. DFC or Dense Fibrillar Component forms the second layer, which surrounds the FC. Finally, the GC or the Granular Component borders the whole thing.
65. rDNA transcription takes place in the FC region or the boundary of FC and DFC. This explains why more of FCs are observed when the rDNA transcription in cells increases.
66. DFC or Dense Fibrillar Component contains a protein known as the fibrillarin. This particular protein is important for the processing of rRNA.
67. Granular Component contains a protein known as the nucleophosmin. Nucleophosmin is also involved in the biogenesis of ribosomes.
68. Formation of Ribosomes takes place in three distinct regions of the Nucleolus. As we mentioned earlier, the Nucleolus Organizer Region of chromosomes contains the genes of the rRNA. Transcription of these genes is initiated in the Fibrillar Center.
69. Dense Fibrillar Component is the region where the RNA synthesis further progresses. 70 types of ribosomal proteins, which are a part of the Nucleolus bind to the transcripts (that take place in FC) in DFC.
70. GC is the region where the pre-ribosomal particles are processed, and they mature.
Cell Nucleus Facts | Nucleoplasm
71. Inside the nucleus, the space that is present between the Nuclear Membrane or the Nuclear Envelope and the Nucleolus is filled with a substance or matrix that is known as the Nucleoplasm.
72. The Nucleoplasm is also known by two other names – Karyolymph or Nuclear Sap.
73. The Nucleoplasm is semi-solid and transparent. It is also granular and slightly acidophilic (that is, it can be stained with acidic dyes).
74. The chemical composition of the Nucleoplasm is very complex. The main component of the matrix is nucleoproteins. However, it also consists of various organic substances and inorganic substances such as minerals, enzymes, proteins, nucleic acids, etc.
Cell Nucleus Facts | Chromatin
75. The Nucleoplasm consists of many elongated and coiled thread-like structures. Basic stains like the basic fuchsin can readily stain these structures.
76. These thread-like structures are known as Chromatins or Chromatin Fibers or Chromatin Structure.
77. Chromatin Fibers are visible only in interphase Nucleus.
78. Chromatin Fibers turn into thick ribbon-like structures during cell division (both mitosis and meiosis).
79. These thick ribbon-like structures are what we know as Chromosomes.
80. Chromatin is composed of proteins and DNA.
81. RNA, in very small quantities, can be present in Chromatin Fibers. Of the total Chromatin present in a cell Nucleus, RNA accounts for nearly 5% only.
82. The proteins that are present in the Chromatin Fibers are mostly histone proteins or basic proteins. Some acidic or non-histone proteins are also present in Chromatin Fibers.
83. If we look at the weight ratio of DNA to protein in Chromatin Fibers, the ratio stands at 1:1.
84. Histones or histone proteins or basic proteins are constituents of all known eukaryotic cells except fungi. So, fungi, at least in terms of Chromatin Fibers, resemble prokaryotes.
85. The Chromatin Fibers are uniformly distributed in the Nucleoplasm. They are twisted but finely anastomosed.
Anastomosis (plural anastomoses) is the opening or connection between two things like passages or cavities that are branching or diverging.
86. Two different types of Chromatin material have been identified so far. They are:
87. Heterochromatin gets darkly stained. It is a condensed region of Chromatin Fibers. These condensed regions are referred to as false nucleoli or karyosomes or chromocenters.
88. Heterochromatin can be seen around the Nucleolus as well as its periphery.
89. Scientists think that Heterochromatin is genetically and metabolically inactive or inert. The reason for this belief is that Heterochromatin contains large amounts of RNA and very less amounts of DNA.
90. Euchromatin is Chromatin Fibers’ diffused region. It is lightly stained. Compared to Heterochromatin, Euchromatin has large amounts of DNA.
Interesting Cell Nucleus Facts: 91-95 | Functions of Cell Nucleus
91. Cell Nucleus is responsible for controlling the metabolic activities of the cell.
92. The Nucleus controls these metabolic activities by controlling enzyme synthesis. These enzymes are required during a cell’s metabolic activities.
93. The Cell Nucleus also controls character inheritance to the off-springs from the parents.
94. The Cell Nucleus is responsible for character development.
95. The genes that off-springs inherit from our parents determine our phenotype (phenotype is the observable physical properties of an organism). The genes that off-springs inherit from our parents are present in chromosomes present in the Nucleus.
Offline: Cell Biology – Cytology, Biomolecules and Molecular Biology by P.S. Verma and V. K. Agarwal | Pages: 631 to 647.