Nucleus Definition, Structure, Diagram, and Functions

Cell biology describes the nucleus is the big organelle, with a membrane-bounded structure that holds the genetic material form of numerous linear DNA molecules arranged into chromosomes, which are the structures that make up the nucleus. In the field of cell biology, the nucleus’s function is to serve as the central point of control for the cells. This is due to the fact that it holds the genetic material that code for the essential functions of cells. 

The nucleus is the organelle that is responsible for maintaining DNA’s integrity and controlling the activities of cells like metabolism, growth and reproduction through the regulation of the expression of genes. The nucleus is by far the largest cell’s cytoplasm. In mammalian cells the average size is about 6 inches. However, there are cells which lack nuclei, namely human red blood cells. There are other cells that have a higher proportion of cells, e.g. osteoclasts.

Nucleus Definition

When it comes to biology,”nucleus” generally refers to the cell’s nucleus. It is described as the organelle within the cell that houses the chromosomes. Some cells do not contain nuclei. If a cell does not have nucleus, it is known as anucleated. In addition to this the term “nucleus” can also be employed in different biological fields. For example, in botany, the term “nucleus” could also be a reference to the central kernel in the nut, or seed, or the central point of the starch granule. The neuroanatomy Nucleus is a nerve cell bodies in the brain and the spinal cord.

In other fields of science the term “nucleus” could refer to the central part or the central area within which the other components are grouped or collected. For example in Physics the term “nucleus” is used to refer to the positively charged center of an atom which usually has neutrons and protons. In Chemistry Nucleus refers to the fundamental arrangement of atoms that occurs in chemical compounds by the substitution of atoms with changing their the structure. In Astronomy the nucleus is the central point of a comet or center or brightest area of a galaxy or nebula. In Meteorology the term “nucleus” refers to a particle in where water vapor molecules gather in the air and create water droplets or crystals of ice.

A nucleus is an enormous double-membraned organelle, which is often called”the “central cell” within the cell due to the fact that it houses the chromosomes that carry all the genes. It is not only found in eukaryotic cells but also on prokaryotic cell lines. In addition to the chromosomes there are various other structures within the nucleus. They are collectively known as nuclear bodies. The fluid part that is found in nucleus cells are known as the nucleoplasm.

Characteristics of Nucleolus

1. Structure: The nucleolus is a membrane-less organelle that is composed of DNA, RNA, and proteins. It is surrounded by chromatin and is usually visible under a microscope as a darkly stained area within the nucleus.
2. Function: The nucleolus is involved in the production of ribosomes, the molecular machines that synthesize proteins. It plays a key role in the assembly of the ribosomal subunits, which are then transported out of the nucleus and into the cytoplasm.
3. Ribosomal RNA synthesis: The nucleolus is responsible for the synthesis and processing of ribosomal RNA (rRNA). This process involves transcription of rRNA genes, modification of the rRNA molecules, and assembly of ribosomal subunits.
4. Organization: The nucleolus is organized into distinct regions, each of which is responsible for a different step in the production of ribosomes. These regions include the fibrillar center, the dense fibrillar component, and the granular component.
5. Size: The size of the nucleolus varies depending on the cell type and the stage of the cell cycle. In general, larger nucleoli are associated with more active protein synthesis.
6. Regulation: The size and activity of the nucleolus are regulated by a variety of factors, including growth signals, stress, and disease. Disruptions in nucleolar function have been linked to a number of diseases, including cancer and neurodegenerative disorders.

Structure of Nucleus/Parts of Nucleus

1. Chromatin/chromosomes

• The nucleic acid (e.g. DNA, the RNA) as well as proteins (e.g. histones) is referred to as chromatin.
• In the course of cell division, cell’s chromatin is compressed to create an it’s a chromosome.
• The fundamental structural unit of chromatin is the nucleosome.
• Each nucleosome consists of a DNA segment wrapped around the histone protein’s cores.
• The primary role of chromatin is pack DNA into a smaller size that fits into the cell.
• There are two main forms of chromatin, the heterochromatin and the euchromatin.
• The structure of euchromatin is loose, allowing replication and transcription, while the heterochromatin is less condensed and, consequently, less active.

Functions of Chromatin/chromosomes

1. DNA Packaging: One of the primary functions of chromatin is to compact DNA into a small enough volume to fit inside the nucleus of a cell. This packaging also helps to protect DNA from damage and allows for efficient storage and transport of genetic information.
2. Gene Expression Regulation: Chromatin structure plays a key role in regulating gene expression. The way in which DNA is packaged within chromatin can affect the accessibility of genes to the cellular machinery that reads and transcribes DNA, thus influencing the expression of genes.
3. DNA Replication and Repair: During cell division, chromosomes must be replicated and distributed to each daughter cell. Chromatin structure and organization play a critical role in the timing and accuracy of DNA replication and repair.
4. Chromosome Segregation: Chromosomes must be properly segregated during cell division to ensure that each daughter cell receives the correct number of chromosomes. Chromatin structure and organization help to ensure that chromosomes are properly aligned and segregated during mitosis and meiosis.
5. Epigenetic Inheritance: Chromatin modifications, such as methylation and acetylation, can be passed on from one generation of cells to the next. These epigenetic modifications can influence gene expression and cellular differentiation.

2. Nuclear DNA

• The nuclear DNA is significant proportions of the genome of a cell (the tiny portion comes from extranuclear DNA that is found in mitochondria or the chloroplasts).
• The DNA outside of the nucleus is known as extranuclear DNA. This extranuclear DNA like cpDNA found in mitochondria, and chloroplasts in is present in multiple copies as there are multiple chloroplasts as well as mitochondria, while there is generally only one nucleus in cells.
• Cells, then have multiple copies of mtDNA as well as cpDNA typically in the thousands.
• Nuclear DNAs are compressed into chromatin-like structures via histones, whereas cpDNA and mtDNA aren’t.

Functions of Nuclear DNA

1. Genetic Information Storage: Nuclear DNA stores all of the genetic information that is required for the development, growth, and function of an organism. This information is organized into discrete units called genes, which contain the instructions for building and maintaining the organism.
2. Gene Expression: Nuclear DNA provides the blueprint for the synthesis of all the proteins and RNA molecules that are required for cellular function. The expression of genes is regulated by various mechanisms, including chromatin structure, transcription factors, and epigenetic modifications.
3. DNA Replication: Nuclear DNA is replicated prior to cell division to ensure that each daughter cell receives a complete copy of the genome. This process is tightly regulated to ensure the fidelity and accuracy of DNA replication.
4. DNA Repair: Nuclear DNA is constantly subjected to damage from various environmental factors such as radiation, chemicals, and free radicals. Cells have a variety of mechanisms for repairing DNA damage to maintain the integrity of the genome.
5. Genetic Variation: Nuclear DNA is subject to genetic mutations that can arise spontaneously or be induced by environmental factors. This variation can provide the raw material for evolutionary change and can also contribute to genetic disorders and disease.
6. Inheritance: Nuclear DNA is passed on from generation to generation through the process of sexual reproduction. The combination of genetic information from two parents leads to genetic diversity among offspring.

3. Nuclear bodies

• A nuclear body is described as a non-membraned mostly proteinsaceous body in the nucleus. As mentioned earlier the nucleolus is considered to be one of nuclear body, and is the most popular.
• It is distinguished by its granular round appearance.
• It is used for the production of ribosomes which are in turn one of the main components of protein synthesis.
• Other nuclear body types are Cajal gems and cajal (Gemini in Cajal bodies) Polymorphic interphase karyosomal connection (PIKA) domains promyelocytic leukemia protein (PML) bodies paraspeckles, splicing speckles as well as perichromatin fibrils and Clastosomes.
• Nuclear bodies are classified as straightforward (type I as well as type II) and more complex (type III Type IVa, type IVa as well as type V).

Functions

• Ribosome biogenesis: Nuclear bodies such as the nucleolus are involved in the synthesis and assembly of ribosomes, the cellular machinery responsible for protein synthesis.
• RNA processing: Some nuclear bodies, such as the Cajal body, are involved in the processing and modification of RNA molecules, including splicing, editing, and transport.
• DNA repair: Nuclear bodies such as the PML nuclear bodies play a role in DNA repair and maintenance of genome stability.
• Transcriptional regulation: Some nuclear bodies, such as the promyelocytic leukemia (PML) nuclear bodies and the Polycomb bodies, are involved in the regulation of gene expression by modulating chromatin structure and epigenetic modifications.
• Stress response: Nuclear bodies such as the nuclear stress bodies and the paraspeckles are formed in response to various types of cellular stress and are involved in the sequestration of proteins and RNA molecules.
• Signaling: Some nuclear bodies, such as the nuclear speckles, are involved in signaling and communication between the nucleus and cytoplasm.

4. Nuclear matrix

• Nuclear matrix functions comparable to the cytoskeleton found in the cell’s cytoplasm.
• The fibrillary structure which provides structural support for the shape and size of the nucleus.
• It is much more dynamic even when compared to the cytoskeleton.
• It is comprised of it’s nuclear layer. The latter is the fibrous and dense network that encircles to the nucleus envelope.

Functions of Nuclear matrix

• Nuclear Architecture: The nuclear matrix provides a framework for the organization of the nucleus and helps to maintain its shape and structure. It also helps to organize and compartmentalize various nuclear components, including chromatin and nuclear bodies.
• DNA Replication and Transcription: The nuclear matrix plays an important role in DNA replication and transcription by providing a scaffold for the assembly of the machinery required for these processes.
• Gene Expression Regulation: The nuclear matrix can influence gene expression by providing a platform for the assembly of transcription factors and other regulatory proteins.
• Chromatin Organization: The nuclear matrix helps to organize and maintain the structure of chromatin, which is essential for proper gene expression and cellular function.
• Nuclear Transport: The nuclear matrix can act as a barrier or filter for the movement of molecules between the nucleus and cytoplasm, contributing to the regulation of nuclear transport.
• Cell Cycle Progression: The nuclear matrix is involved in the regulation of cell cycle progression, particularly during mitosis and cytokinesis, by providing a structural framework for the organization and segregation of chromosomes.

5. Nucleoplasm

• The term “nucleoplasm” refers to the nucleus’ protoplasm like the cytoplasm found is found in the other parts of the cell.
• The nucleoplasm is made up of different components (e.g. the nuclear body, chromosomes the nuclear matrix) that are contained within an envelope called the nuclear.
• The liquid component of the nucleoplasm is referred to as the nucleosol (just as the cytosol is to it’s cytoplasm).
• Nucleoplasm is the substance that forms a gelatinous layer inside the nuclear envelope.
• Also known as karyoplasm, this semi-aqueous substance is similar to the cytoplasm . It is made up of mainly water, dissolved enzymes, salts, and organic molecules suspended in.
• The nucleolus as well as chromosomes are protected by nucleoplasm which serves to cushion and protect content of nucleus.
• Nucleoplasm can also support the nucleus, helping it keep its shape. Furthermore, it provides the medium through which various substances like enzymes and nucleotides (DNA and subunits of RNA) are transported through the nucleus. Substances exchange between nucleoplasm and the cytoplasm through nucleoplasmic pores.

Functions of Nucleoplasm

1. Gene Expression: Nucleoplasm plays a critical role in gene expression by providing a platform for the assembly of the transcriptional machinery required for the transcription of DNA into RNA.
2. RNA Processing: The nucleoplasm contains various enzymes and proteins that are required for the processing of RNA, including splicing, capping, and polyadenylation.
3. Nuclear Transport: Nucleoplasm is involved in the transport of molecules between the nucleus and the cytoplasm. It contains nuclear pores, which allow for the regulated exchange of molecules between the two compartments.
4. DNA Replication and Repair: Nucleoplasm provides the environment and molecular components required for DNA replication and repair. It contains various enzymes and proteins that are involved in these processes.
5. Chromatin Organization: Nucleoplasm helps to organize and maintain the structure of chromatin, which is essential for proper gene expression and cellular function.
6. Signaling: Nucleoplasm contains various signaling molecules, including transcription factors and enzymes that can activate or inhibit gene expression in response to various stimuli.

In summary, the nucleoplasm plays a critical role in gene expression, RNA processing, nuclear transport, DNA replication and repair, chromatin organization, and cellular signaling. It is a complex and dynamic environment that is essential for the proper functioning of the nucleus and the cell as a whole.

6. Nuclear envelope

• The nucleus’s envelope (also known as the nucleus membrane) is a type of biological membrane that surrounds the nucleus.
• As with cell membranes, the nuclear membrane is a bilipid layer. So, the nuclear membrane functions in a similar way to a cell membrane for regulating the flow and exit of substances.
• The nuclear envelope is a cellular structure with pores that control the flow of molecules between the nucleoplasm as well as the celluplasm. It is inaccessible to large molecules. This is why it is able to separate the contents of the nucleus from the cell tissue and allows for the passage of specific molecules.
• Nuclear transport for large molecules (e.g. proteins or RNAs) takes place via active transport system that contains carrier proteins, whereas the transport of smaller molecules and ions is done by passively passing through these pores in the nucleus.

Functions of Nuclear envelope

1. Nuclear Organization: The nuclear envelope provides a physical barrier between the nucleus and the cytoplasm, allowing for the organization and segregation of nuclear components, including chromatin, nucleoli, and nuclear bodies.
2. Nuclear Transport: The nuclear envelope regulates the transport of molecules between the nucleus and the cytoplasm. It contains nuclear pores, which allow for the selective exchange of molecules between the two compartments.
3. Gene Expression Regulation: The nuclear envelope can influence gene expression by regulating the movement of transcription factors and other regulatory proteins between the nucleus and the cytoplasm.
4. Chromatin Organization: The nuclear envelope helps to organize and maintain the structure of chromatin, which is essential for proper gene expression and cellular function.
5. DNA Replication and Repair: The nuclear envelope is involved in the regulation of DNA replication and repair by providing a scaffold for the assembly of the machinery required for these processes.
6. Cell Cycle Progression: The nuclear envelope is involved in the regulation of cell cycle progression, particularly during mitosis and cytokinesis, by providing a structural framework for the organization and segregation of chromosomes.

In summary, the nuclear envelope plays a critical role in maintaining the organization and function of the nucleus, regulating gene expression, and supporting essential cellular processes such as nuclear transport, DNA replication and repair, and cell cycle progression.

7. Lobes

• The nucleus could be described as bilobed multi-lobed or tri-lobed based on the amount of lobes.
• White blood cells are an illustration one with lobed nucleus.

Functions of Lobes

• Nuclear Organization: The lobes in the nucleus can provide a degree of organization by separating different nuclear components, such as chromatin, nucleoli, and nuclear bodies, into discrete regions.
• Gene Expression Regulation: Some studies suggest that the lobes in the nucleus may play a role in the regulation of gene expression by separating active and inactive chromatin domains into different lobes.
• Nuclear Envelope Interaction: The lobes in the nucleus can interact with the nuclear envelope, allowing for the selective exchange of molecules between the nucleus and cytoplasm in a region-specific manner.
• Cell Differentiation: The presence of lobes in the nucleus has been associated with certain stages of cell differentiation in certain types of white blood cells.

8. Nucleolus

• In the nucleus, there is a thick, non-membrane structure that is made up of RNA as well as proteins referred to as the nucleolus.
• A few eukaryotic organisms have nuclei that contain as many as four nucleoli.
• The nucleolus is home to organizers for nucleolar RNA that are part of chromosomes that have genes for ribosome synthesizing on them. The nucleolus assists in the production of Ribosomes by transcribing and joining subunits of ribosomal DNA. These subunits join and form a “ribosome” the process of protein synthesis.
• The nucleolus vanishes after cells divide and is rebuilt following the cell division has ended.

Functions of Nucleolus

1. Ribosome Biogenesis: The nucleolus is the site of ribosome biogenesis, which involves the assembly of ribosomal RNA (rRNA) and ribosomal proteins into functional ribosomes. The nucleolus contains multiple sub-compartments that are specialized for different stages of ribosome biogenesis.
2. rRNA Transcription: The nucleolus is the site of rRNA transcription, which is carried out by RNA polymerase I. The transcription of rRNA is an essential step in ribosome biogenesis.
3. rRNA Processing: The nucleolus contains various enzymes and factors that are required for the processing and modification of rRNA. These processes include cleavage, folding, and chemical modification of rRNA.
4. Assembly of Ribosomal Subunits: The nucleolus is involved in the assembly of ribosomal subunits, which are the functional components of ribosomes. The assembly of ribosomal subunits involves the incorporation of rRNA and ribosomal proteins into pre-ribosomal particles.
5. Cell Cycle Regulation: The nucleolus can play a role in the regulation of the cell cycle by sensing and responding to various signals, including DNA damage and nutrient availability. These signals can affect the activity of ribosome biogenesis and protein synthesis.

In summary, the nucleolus is a critical structure within the nucleus that plays a central role in ribosome biogenesis, rRNA transcription and processing, ribosomal subunit assembly, and cell cycle regulation. Defects in nucleolar function have been linked to a variety of diseases, including cancer and developmental disorders.

How Nucleus are fomed within cell, step by step Explain or Procedure?

The formation of the nucleus within a cell occurs during the process of cell division, which involves the replication and segregation of the genetic material. Here are the step-by-step procedures for the formation of the nucleus within a cell:

1. Interphase: During interphase, the cell grows, replicates its DNA, and prepares for cell division. The genetic material is packaged into chromatin, which is dispersed throughout the nucleus.
2. Prophase: During prophase, the chromatin condenses into visible chromosomes, which become visible under a microscope. The nuclear envelope breaks down, and the nucleolus disappears.
3. Metaphase: During metaphase, the chromosomes align at the equator of the cell, known as the metaphase plate, and the spindle fibers attach to the kinetochores, which are protein structures on the chromosomes.
4. Anaphase: During anaphase, the spindle fibers pull the sister chromatids apart, separating them into two sets of chromosomes. The cell elongates as the spindle fibers push the poles of the cell apart.
5. Telophase: During telophase, the chromosomes arrive at the opposite poles of the cell, and a new nuclear envelope begins to form around each set of chromosomes. The chromatin begins to decondense, and the nucleolus reappears.
6. Cytokinesis: In animal cells, cytokinesis involves the formation of a cleavage furrow, which divides the cytoplasm into two daughter cells. In plant cells, cytokinesis involves the formation of a cell plate, which eventually becomes a new cell wall.
7. Interphase: After cell division is complete, the two daughter cells enter interphase, and the process of cell growth and DNA replication begins again.

In summary, the formation of the nucleus within a cell involves the condensation of chromatin into chromosomes, the breakdown and reformation of the nuclear envelope, and the segregation of the genetic material into two daughter cells. These processes are tightly regulated and are essential for the proper functioning of the cell.

How to study Nucleus?

Studying the nucleus within a cell can be done using various techniques and approaches, depending on the specific question being addressed. Here are some common methods used to study the nucleus:

1. Microscopy: The structure of the nucleus can be visualized using various forms of microscopy, including light microscopy, fluorescence microscopy, and electron microscopy. These techniques can reveal the morphology, organization, and composition of the nucleus, as well as the localization of specific molecules within the nucleus.
2. Biochemical analysis: The components of the nucleus can be extracted and analyzed using biochemical techniques, such as protein purification and DNA sequencing. These approaches can provide insights into the molecular composition and function of the nucleus.
3. Genetic manipulation: The function of the nucleus can be studied by genetically manipulating the cells to alter the expression or activity of specific genes or proteins. This can be done using techniques such as gene knockdown or knockout, overexpression, or gene editing using CRISPR/Cas9.
4. Live-cell imaging: The behavior of the nucleus within a living cell can be studied using live-cell imaging techniques. This allows for the observation of dynamic processes, such as nuclear transport, DNA replication, and chromatin remodeling, in real-time.
5. Computational modeling: The behavior of the nucleus can be simulated using computational models that incorporate biophysical and biochemical principles. These models can provide insights into the underlying mechanisms that govern the behavior of the nucleus.

In summary, studying the nucleus within a cell can be achieved using a range of techniques, including microscopy, biochemical analysis, genetic manipulation, live-cell imaging, and computational modeling. The choice of method will depend on the specific question being addressed and the level of detail required to answer it.

Functions of Nucleus

The nucleus serves as a location for gene transcription, which is separated from the place of transcription in the cytoplasm. This allows levels of gene control that are not accessible to prokaryotes. The primary purpose of the cell’s nucleus is to regulate gene expression as well as to facilitate reproduction of DNA in the cycle of cell growth.

1. Control of Gene Expression: The nucleus controls the expression of genes by regulating the transcription and translation of DNA into RNA and proteins. This is achieved through a variety of mechanisms, including chromatin remodeling and the binding of transcription factors to DNA.
2. Storage of Genetic Material: The nucleus stores the genetic material of the cell in the form of DNA. This DNA is organized into chromosomes and is protected by a double membrane called the nuclear envelope.
3. DNA Replication: The nucleus is responsible for DNA replication, which is necessary for cell division and the transmission of genetic information from one generation to the next.
4. RNA Synthesis: The nucleus is also responsible for the synthesis of RNA, which is essential for protein synthesis. This process occurs through the transcription of DNA into RNA, which then moves out of the nucleus and into the cytoplasm for translation.
5. Cell Division: The nucleus plays a key role in cell division by controlling the replication and distribution of chromosomes. It is responsible for the organization of chromosomes during mitosis and meiosis.
6. Maintenance of Cellular Homeostasis: The nucleus helps to maintain cellular homeostasis by regulating the expression of genes involved in cellular processes such as metabolism, growth, and differentiation.

In summary, the nucleus is a critical organelle that plays a central role in the control of gene expression, storage of genetic material, DNA replication, RNA synthesis, cell division, and maintenance of cellular homeostasis.

• It regulates the genetic characteristics of an animal.
• Organelles are also involved in the synthesis of proteins as well as development, cell division and differentiation.
• Storage of hereditary material the genes that are made up of thin and long DNA (deoxyribonucleic acid) strings, known as Chromin.
• Protein storage and the storage of RNA (ribonucleic acid) within the nucleolus.
• The nucleus is the site for transcription, where messenger (mRNA) (mRNA) are made to enable protein production.
• In the process of cell division the chromatins are placed in chromosomes within the nucleus.
• Production of Ribosomes (protein factories) within the nucleolus.
• Transport of regulatory factors or energy molecules by nuclear pores.

Diseases are associated with defects in the nucleus

Defects in the nucleus can lead to various diseases. Here are some examples:

1. Cancer: Cancer is often caused by mutations in genes that regulate cell growth and division. These mutations can occur in the nucleus, leading to uncontrolled cell growth and the formation of tumors.
2. Genetic disorders: Many genetic disorders are caused by mutations in genes that are located in the nucleus. These mutations can affect the structure or function of proteins, leading to a wide range of symptoms depending on the affected gene.
3. Neurodegenerative diseases: Several neurodegenerative diseases, such as Alzheimer’s disease and Huntington’s disease, are caused by the accumulation of abnormal proteins in the nucleus and cytoplasm of neurons.
4. Immunodeficiency disorders: Some immunodeficiency disorders, such as severe combined immunodeficiency (SCID), are caused by mutations in genes that regulate the development and function of immune cells in the nucleus.
5. Progeria: Progeria is a rare genetic disorder that causes premature aging. It is caused by a mutation in the LMNA gene, which is located in the nucleus and encodes a protein that helps maintain the shape of the nucleus.
6. Muscular dystrophy: Muscular dystrophy is a group of genetic disorders that cause progressive muscle weakness and degeneration. Many forms of muscular dystrophy are caused by mutations in genes that are located in the nucleus and are involved in muscle function and development.

Biological Importance of Nucleus

The nucleus is the biggest cell’s cytoplasmic organelle in mammals. In mammalian cells the average size is about 6um. There are some cells deficient in nuclei, for instance human red blood cell, there are certain cells with more nuclei e.g. osteoclasts. This implies that the osteoclasts have a greater degree of activity in the sense of regulation of genes than Red blood cells. After maturation, red blood cells shed their nucleus and provide more affinity to gasses, e.g. oxygen.

Distribution of Nucleus

On the basis of the cell’s presence or absence, several cell types are categorized. The many varieties are described below:

1. Uninucleate cell: It is also known as monokaryotic cells, which are predominantly plant cells with a single nucleus.
2. Bi-nucleate cell: Also known as a dikaryotic cell. It includes two nuclei simultaneously. One paramecium (with mega and micronuclei), balantidium, liver cells, and cartilage cells are examples.
3. Multinucleate cells: It is also referred to as a polynucleated cell since it has more than two nuclei simultaneously. For example, plants latex cells and latex tubes. striated muscle cells and bone marrow cells in mammals.
4. Enucleate cells: Cells lacking a nucleus are known as enucleate cells. Yet, some live cells, such as mature phloem sieve tubes and mature mammalian RBCs, lack nuclei.

In conclusion, we have learned about the structure and functions of the nucleus. Also, we have learned about distinct cell types based on the presence or lack of the nucleus.

FAQ

References

• Cooper GM. The Cell: A Molecular Approach. 2nd edition. Sunderland (MA): Sinauer Associates; 2000. Chapter 8, The Nucleus. Available from: https://www.ncbi.nlm.nih.gov/books/NBK9845/
• https://www.biologyonline.com/dictionary/nucleus
• https://micro.magnet.fsu.edu/cells/nucleus/nucleus.html