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Can you believe the cell nucleus is the largest organelle of the cell and holds approximately 2 meters of DNA? Read this BiologyWise article for more such interesting facts about this structure.

The cell nucleus is a compact organelle found in every eukaryotic cell. In fact, its presence is used as a differentiating point between eukaryotes and prokaryotes. As the nucleus houses the primary components of a eukaryotic cell, you can imagine its importance in the overall functioning of the cell. Functionally, one of the interesting cell nucleus activities is its active participation in protein synthesis. Continue reading to know some of the most interesting facts about this structure.

Interesting Facts About Cell Nuclei

Cell nucleus is an organized organelle, which is responsible for major cellular activities of a eukaryotic organism. Even though majority of the eukaryotic cells have a single nucleus, there are some modifications. For example; a matured human red blood cell lacks nucleus (enucleate), a paramecium contains two nuclei, and a smile mold contains millions of nuclei (multinucleate). Detailed information about cell nucleus has been presented below.

Discovery

In a biology report, the cell nucleus was observed for the first time by Antonie Philips van Leeuwenhoek, the father of microbiology. But the actual credit for discovery of this structure goes to Robert Brown, a Scottish botanist. In his 1831 paper publication, he mentioned the presence of opaque spots in plant tissues. He assumed the spots as significant constituents of cells and termed them as nucleus.

Location

The cell nucleus is located in the middle of the cell, which is surrounded by the cytoplasm. However, this is not always true for all types of eukaryotic cells. In some, it is present towards the border of the cell. This is applicable in case of plant cells, in which a large vacuole is present in the near center of the cells. Also, during cell division, the location of the cell nucleus deviates and holds an off-center position.

Size

It is the largest and most prominent organelle in a cell. The actual size of the cell nucleus varies from one organism to another. Also, the dimension of the nucleus changes with respect to the particular stage in the cell cycle. On an average, the nucleus of a mammalian cell is about 6 micrometers in diameter.

Structure

Coming to the structure, a double membrane separates it from the remaining parts of the cell. Structurally, this nuclear membrane maintains continuity with the membrane of rough endoplasmic reticulum. This is crucial for transportation of nuclear materials from inside to the outside during the process of protein synthesis. The nuclear membrane is also responsible for maintaining a near-circular shape of the nucleus.

Composition

The cell nucleus is made up of a double layered nuclear membrane, nucleolus (origin of ribosomes and RNA), chromatin (makes up chromosomes), chromosomes (hereditary material), nucleosome (made up of proteins and DNA), and histone proteins (bind DNA in a compact form). To be more precise, the cell nucleus contains a maximum amount of hereditary material for a cell.

Functions

The main functions of a cell nucleus include regulating cell metabolism, cell division, and gene expression, in addition to controlling protein synthesis. Hence, it won't be wrong to say that the cell nucleus is functionally the most important organelle. It regulates all cellular activities, either directly or indirectly. It is for this reason that the nucleus of a cell is considered as the 'brain' or 'control center' of a eukaryotic cell.

So, aren't these facts interesting to note? As far as synthesis of proteins is concerned, the transcription phase is carried out in the cell nucleus, while the later translation phase occurs outside the nucleus, in the cell cytoplasm. Other than this structure, some amount of the hereditary material is present in the mitochondrion organelle.

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Can you believe the cell nucleus is the largest organelle of the cell and holds approximately 2 meters of DNA? Read this BiologyWise article for more such interesting facts about this structure. The cell nucleus is a compact organelle found in every eukaryotic cell.

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“Nucleus.” Encyclopædia Britannica. Encyclopædia Britannica, inc. Accessed October 9, 2021. https://www.britannica.com/science/nucleus-biology.
“Nucleus Structure Crucial to Understanding Diseases Discovered.” ScienceDaily. ScienceDaily, February 8, 2013. https://www.sciencedaily.com/releases/2013/02/130208110255.htm.
“Translation.” Encyclopædia Britannica. Encyclopædia Britannica, inc. Accessed October 9, 2021. https://www.britannica.com/science/translation-genetics.
Shaziya Allarakha, MD. “What Are the 3 Functions of the Nucleus?” MedicineNet. MedicineNet, February 12, 2021. https://www.medicinenet.com/what_are_the_3_functions_of_the_nucleus/article.htm.
“The Nuclear Envelope.” Encyclopædia Britannica.
Bailey, Regina. “What Is the Nucleus?” ThoughtCo. ThoughtCo, November 6, 2019. https://www.thoughtco.com/the-cell-nucleus-373362. Encyclopædia Britannica, inc. Accessed October 9, 2021. https://www.britannica.com/science/cell-biology/The-nuclear-envelope#ref37405.

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The Agency for Science, Technology and Research (A*STAR), based in Singapore, discovered in 2013 that the deviation of genes from their correct position can have dire consequences for the human body, emphasizing the importance of proteins lamin A (Lmna) and lamin B receptor (Lbr) in holding genes in the form of heterochromatin. The slightest relocation of these genes will snowball, causing major bodily harm. Beginning with the malfunction of these genes, heart failure, vascular disease and muscle wasting will follow.

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Nuclear pores: Abundant across the nuclear envelope's phospholipid bilayer, nuclear pores allow materials to enter and exit the nucleus, moving from the cytoplasm to the nucleoplasm.

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Chromatin: Chromatin is comprised of subunits known as nucleosomes, sections of DNA which are looped around histone "anchors". These nucleosomes are then packed into solenoids, a spiral-like structure in which more histones are added to support the chromatin structure. DNA in eukaryotic cells, unlike prokaryotic cells is extremely condensed. 23 pairs of chromosomes condense further out of chromatin prior to cell division.

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Nucleoplasm: A semi-aqueous substance similar to cytoplasm. The nucleoplasm cushions and protects the contents of the nucleus, holding it’s structure.

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Nuclear Envelope: A double membrane that separates the organelle from cytoplasm, encompassing the contents of the nucleus. Similar to the cell membrane, the nuclear envelope is composed of a phospholipid bilayer, which allows the envelope to regulate the transfer of materials and contributes to the structure of the nucleus.

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Nucleolus: A dense structure containing RNA and proteins along with nucleolar organizers, the nucleolus' main function is the formation of ribosomal RNA and ribosome biogenesis. The nucleolus transcribes and assembles rRNA subunits, which combine during protein synthesis, creating ribosomes.

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Controlling cell growth and division - The storage of DNA in the form of chromatin within the nucleus, packed and wound tightly with the help of histones, prevents it from spilling out during cell division. DNA is unwinded prior to division, forming chromosomes which are then split.

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Directing protein and enzyme synthesis - After transportation through the nuclear pores in the nuclear envelope, the mRNA molecules attach to ribosomes in the cytoplasm and endoplasmic reticulum, where they are translated and proteins are synthesized. Proteins which are then expelled from the cell will function as enzymes, crucial to the body's chemical processes.

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Serving as a site for messenger ribonucleic acid synthesis - The genetic code is first transcribed into a range of mRNA molecules, each molecule containing the necessary information to create a protein. Although mRNA is most common, the nucleus is also responsible for the synthesis of other types of RNA involved in the process of protein synthesis. The nucleus additionally serves to regulate the amounts of mRNA supplied to the cytoplasm, a quantity that varies from cell to cell.

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The nucleus carries the genetic code of an organism - The primary function of the nucleus is actually to express the genetic information that it houses, coding which determines the amino acid chains and the construction of specific proteins. The deoxyribonucleic acid molecules present in the organelle allow the cell to maintain its unique identity throughout the processes of cell growth and division. Controls the hereditary characteristics of an organism.

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The nucleus is by far the most important eukaryotic organelle, it's one of the cell's defining characteristics and  set eukaryotic cells apart from prokaryotic cells!

Serves as the cell’s genetic library and facilitates the interpretation of these genes

The nucleus provides separation of DNA from the cytoplasm and protein synthesis, allowing eukaryotic cells to better regulate protein and RNA production.

It is the main control center of the cell, and functions similarly to a brain.

A eukaryotic cell cannot survive without a nucleus!

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Cell nuclei are approximately 5 micrometers in diameter, and are composed of 5 major components.

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The four major functions of the nucleus are outlined through the process of transcription and translation.

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The nucleus was the first organelle to be discovered by scientists.

10% of the cell’s volume is occupied by the nucleus.

Although it is not common, some cells do develop with more than a single nucleus. Double the brainpower!

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Genes relocated from their correct position in the nucleus cause them to malfunction and this may lead to the heart, blood vessels and muscles breaking down.

Scientists from Singapore and Germany have identified that the proteins lamin A ( Lmna) and lamin B receptor ( Lbr) are essential for holding silent genes in their correct position at the edge of the nucleus, in the form of heterochromatin. A deviation from their normal position will cause the genes to malfunction, leading to heart failure, vascular disease and muscle wasting.

For hundreds of years before this discovery, scientists were puzzled by why heterochromatin clustered at the edge of the nucleus and how it was relevant to normal cell function. This recent discovery will enable scientists to gain a better understanding of the diseases of the heart and muscles, and find cures for them in the future.

The findings by Audrey Wang and Colin Stewart of A*STAR's Institute of Medical Biology and Irina Solovei, Boris Joffe and Heinrich Leonhardt of the Ludwig Maximillian University in Munich, Germany, were recently published in the prestigious journal Cell.

The nucleus -- the brain of the cell -- carries all the information, in the form of chromatin necessary to help a cell grow, thrive, and reproduce, in the form of DNA packed into chromatin. Hence, understanding how chromatin is organised in the nucleus is important to understanding disease and normal processes such as ageing. The scientists showed that the two proteins lamin A and lamin B receptor are important to the organisation of chromatin in the nucleus. Using mouse models, they demonstrated that in the absence of the two proteins, heterochromatin collapsed into the nuclear centre. This disrupted gene expression and affected skeletal muscle development, resulting in muscle failure .

Professor Stewart, Research and Assistant Director of IMB, said, "These findings will provide new insights into how diseases arise and may help explain how mutations in lamin proteins result in a variety of different syndromes. In particular, we are extending these findings to explore how changes in chromatin position may contribute to heart failure. Moving forward, we will collaborate with cardiologists and vascular clinicians at SGH and NUHS to translate these findings to benefit patients."

Professor Birgitte Lane, Executive Director of IMB, said, "I would like to congratulate Colin and the team for this important piece of research. It brings us a step closer to understanding the nucleus and to developing new treatments for common diseases. It could be particularly relevant for Singapore, as we, like other developed nations, are facing an ageing population, and heart failure, vascular disease and muscle wasting all increase with age."

Journal Reference:

Irina Solovei, Audrey S. Wang, Katharina Thanisch, Christine S. Schmidt, Stefan Krebs, Monika Zwerger, Tatiana V. Cohen, Didier Devys, Roland Foisner, Leo Peichl, Harald Herrmann, Helmut Blum, Dieter Engelkamp, Colin L. Stewart, Heinrich Leonhardt, Boris Joffe. LBR and Lamin A/C Sequentially Tether Peripheral Heterochromatin and Inversely Regulate Differentiation. Cell, 2013; 152 (3): 584 DOI: 10.1016/j.cell.2013.01.009

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heart disease; stroke prevention; epigenetics; diseases and conditions; genes; human biology; nervous system; sickle cell anemia

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Nucleus structure crucial to understanding diseases discovered

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Scientists from Singapore and Germany have identified that the proteins lamin A and lamin B receptor are essential for holding silent genes in their correct position at the edge of the nucleus, in the form of heterochromatin . A deviation from their normal position will cause the genes to malfunction, leading to heart failure, vascular disease and muscle wasting.