Nucleoplasm

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The protoplasmic material of the nucleus including the nucleolus labelled as nucleoplasm. Diagram human cell nucleus.svg
The protoplasmic material of the nucleus including the nucleolus labelled as nucleoplasm.

The nucleoplasm, also known as karyoplasm, [1] is the type of protoplasm that makes up the cell nucleus, the most prominent organelle of the eukaryotic cell. It is enclosed by the nuclear envelope, also known as the nuclear membrane. [2] The nucleoplasm resembles the cytoplasm of a eukaryotic cell in that it is a gel-like substance found within a membrane, although the nucleoplasm only fills out the space in the nucleus and has its own unique functions. The nucleoplasm suspends structures within the nucleus that are not membrane-bound and is responsible for maintaining the shape of the nucleus. [2] The structures suspended in the nucleoplasm include chromosomes, various proteins, nuclear bodies, the nucleolus, nucleoporins, nucleotides, and nuclear speckles. [2]

Contents

The soluble, liquid portion of the nucleoplasm is called the karyolymph [3] nucleosol, [4] or nuclear hyaloplasm.

History

Polish-German botanist and namer of nucleoplasm, Eduard Strasburger. Plate 03 Professor E. Strassburger, Photograph album of German and Austrian scientists (cropped).png
Polish-German botanist and namer of nucleoplasm, Eduard Strasburger.

The existence of the nucleus, including the nucleoplasm, was first documented as early as 1682 by the Dutch microscopist Leeuwenhoek and was later described and drawn by Franz Bauer. [5] However, the cell nucleus was not named and described in detail until Robert Brown's presentation to the Linnean Society in 1831. [6] The nucleoplasm, while described by Bauer and Brown, was not specifically isolated as a separate entity until its naming in 1882 by Polish-German scientist Eduard Strasburger, one of the most famous botanists of the 19th century, and the first person to discover mitosis in plants. [7]

Role

Many important cell functions take place in the nucleus, more specifically in the nucleoplasm. The main function of the nucleoplasm is to provide the proper environment for essential processes that take place in the nucleus, serving as the suspension substance for all organelles inside the nucleus, and storing the structures that are used in these processes. [2] 34% of proteins encoded in the human genome are ones that localize to the nucleoplasm. [2] These proteins take part in RNA transcription and gene regulation in the nucleoplasm. [2] Proteins located in the nucleoplasm are involved in the activation of genes that are used in the cell cycle. [8] Some nucleoporins which typically make up the nuclear pore, can be mobile and participate in the regulation of gene expression in the nucleoplasm. [8] [9] The nuclear pore is where molecules travel from inside the nucleoplasm to the cytoplasm and vice versa. [9] The nucleoplasm is also a route for many molecules to travel through. [9] Smaller molecules are able to pass freely through the nuclear pore to get into and out of the nucleoplasm, while larger proteins need the help of receptors on the surface of the nuclear envelope. [9] The nuclear matrix is also believed to be contained in the nucleoplasm where it functions to maintain the size and shape of the nucleus, in a role similar to that of the cytoskeleton found in the cytoplasm. [10] However, the existence and the exact function of the nuclear matrix remain unclear and heavily debated.

Composition

The nucleoplasm is a highly viscous liquid that is enveloped by the nuclear membrane and consists mainly of water, proteins, dissolved ions, and a variety of other substances including nucleic acids and minerals.

Proteins

Nearly a third of the human protein-coding genes (6784 genes) [2] have been found to localize to the nucleoplasm via targeting by a nuclear localization sequence (NLS). Cytosolic proteins, known as importins, act as receptors for the NLS, escorting the protein to a nuclear pore complex to be transported into the nucleoplasm. [11] Proteins in the nucleoplasm are mainly tasked with participating in and regulating cellular functions that are DNA-dependent, including transcription, RNA splicing, DNA repair, DNA replication, and a variety of metabolic processes. [2] These proteins are divided into histone proteins, a class of proteins that bind to DNA and give chromosomes their shape and regulate gene activity, [12] and non-histone proteins.

The nucleoplasm contains many enzymes that are instrumental in the synthesis of DNA and RNA, including DNA polymerase and RNA polymerase which function in DNA replication and RNA transcription, respectively. Additionally, the nucleoplasm is host to many of the enzymes that play essential roles in cellular metabolism. NAD+ synthase is stored in the nucleoplasm and functions in electron transport and redox reactions involved with the electron transport chain and synthesis of adenosine triphosphate (ATP). [13] Pyruvate kinase is also found in the nucleoplasm in significant quantities; this enzyme is involved in the final step of glycolysis, catalyzing the conversion of phosphoenolpyruvate (PEP) to pyruvate along with the phosphorylation of adenosine diphosphate (ADP) to ATP. [14] Importantly, the nucleoplasm contains co-factors and co-enzymes, including acetyl-CoA, which plays a vital role in the citric acid cycle, [15] and ATP, which is involved in energy storage and transfer.

Ions

An example of the sodium-potassium pump, a P-type ATPase, which controls the ionic gradient across the cell membrane and the nuclear envelope as well as the ionic makeup of the nucleoplasm through the selective pumping of sodium and potassium ions. NaKpompe2.jpg
An example of the sodium-potassium pump, a P-type ATPase, which controls the ionic gradient across the cell membrane and the nuclear envelope as well as the ionic makeup of the nucleoplasm through the selective pumping of sodium and potassium ions.

The ionic composition of the nucleoplasm is crucial in maintaining homeostasis within the cell and the organism as a whole. Ions that have been documented in the nucleoplasm include sodium, potassium, calcium, phosphorus, and magnesium. These ions are key players in a variety of biological functions. Sodium and potassium play key roles in the sodium-potassium pump, a transmembrane ATPase that pumps three sodium ions out of the cell for every two potassium ions it pumps into the cell, creating an ionic gradient. [16] While this pump is generally considered to be a plasma membrane protein, its presence has been recorded in the nuclear envelope, controlling the ionic gradient between the cytoplasm and nucleoplasm of the cell and contributing to the homeostasis of calcium within the cell. [17] These ions also determine the concentration gradient that exists between the cytoplasm and nucleoplasm, serving to control the flow of ions across the nuclear envelope. [18] They are important in maintaining the osmolarity of the nucleoplasm which in turn provides structural integrity to the nuclear envelope as well as the organelles suspended in the dense nucleoplasm.

Similarity to cytoplasm

Nucleoplasm is quite similar to the cytoplasm, with the main difference being that nucleoplasm is found inside the nucleus while the cytoplasm is located inside the cell, outside of the nucleus. Their ionic compositions are nearly identical due to the ion pumps and permeability of the nuclear envelope, however, the proteins in these two fluids differ greatly. Proteins in the cytoplasm are termed cytosolic proteins which are produced by free ribosomes while proteins that localize to the nucleoplasm must undergo processing in the endoplasmic reticulum and golgi apparatus before being delivered to the nucleoplasm as part of the secretory pathway. These proteins also differ in function, as proteins that localize to the nucleoplasm are largely involved in DNA-dependent processes including cell division and gene regulation, while cytosolic proteins are mainly involved in protein modification, mRNA degradation, metabolic processes, signal transduction, and cell death. [19]

The cytoplasm and the nucleoplasm are both highly gelatinous structures enclosed by membranous structures- the plasma membrane and the nuclear envelope, respectively. However, while the cytoplasm is contained by a single lipid bilayer membrane, the nuclear envelope that compartmentalizes the nucleoplasm consists of two separate lipid bilayers- an outer membrane and an inner membrane. [20] The cytoplasm is also found in all known cells while nucleoplasm is only found in eukaryotic cells, as prokaryotic cells lack a well-defined nucleus and membrane-bound organelles. Additionally, during cell division, the cytoplasm divides during cytokinesis, while the nucleoplasm is released with the dissolution of the nuclear envelope, refilling only after the nuclear envelope reforms.

The organelles and other structures within the cytoplasm and nucleoplasm are organized by protein filaments within their respective compartments. The cytoplasm contains the cytoskeleton, a network of protein filaments found in all cells, while the nucleoplasm is believed to contain the nuclear matrix, a hypothetically analogous network of filaments that organizes the organelles and genetic information within the nucleus. While the structure and function of the cytoskeleton have been well documented, the exact function, and even the presence, of the nuclear matrix is disputed. [21] While the exact composition of the nuclear matrix has not been confirmed, type V intermediate filaments, known as nuclear lamins, have been documented in the nucleoplasm, functioning in the structural support of the nucleus as well as the regulation of DNA replication, transcription, and chromatin organization. [22] Cytoplasmic streaming, the circular flow of cytoplasm driven by the cytoskeleton, has been well documented in the cytoplasm, aiding in intracellular transport, but this process has not been documented in the nucleoplasm.

Related Research Articles

<span class="mw-page-title-main">Cell (biology)</span> Basic unit of many life forms

The cell is the basic structural and functional unit of all forms of life. Every cell consists of cytoplasm enclosed within a membrane; many cells contain organelles, each with a specific function. The term comes from the Latin word cellula meaning 'small room'. Most cells are only visible under a microscope. Cells emerged on Earth about 4 billion years ago. All cells are capable of replication, protein synthesis, and motility.

<span class="mw-page-title-main">Cytoplasm</span> All of the contents of a eukaryotic cell except the nucleus.

In cell biology, the cytoplasm describes all material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The main components of the cytoplasm are the cytosol, the organelles, and various cytoplasmic inclusions. The cytoplasm is about 80% water and is usually colorless.

<span class="mw-page-title-main">Cell nucleus</span> Eukaryotic membrane-bounded organelle containing DNA

The cell nucleus is a membrane-bound organelle found in eukaryotic cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, and a few others including osteoclasts have many. The main structures making up the nucleus are the nuclear envelope, a double membrane that encloses the entire organelle and isolates its contents from the cellular cytoplasm; and the nuclear matrix, a network within the nucleus that adds mechanical support.

Cell biology is a branch of biology that studies the structure, function, and behavior of cells. All living organisms are made of cells. A cell is the basic unit of life that is responsible for the living and functioning of organisms. Cell biology is the study of the structural and functional units of cells. Cell biology encompasses both prokaryotic and eukaryotic cells and has many subtopics which may include the study of cell metabolism, cell communication, cell cycle, biochemistry, and cell composition. The study of cells is performed using several microscopy techniques, cell culture, and cell fractionation. These have allowed for and are currently being used for discoveries and research pertaining to how cells function, ultimately giving insight into understanding larger organisms. Knowing the components of cells and how cells work is fundamental to all biological sciences while also being essential for research in biomedical fields such as cancer, and other diseases. Research in cell biology is interconnected to other fields such as genetics, molecular genetics, molecular biology, medical microbiology, immunology, and cytochemistry.

<span class="mw-page-title-main">Cytosol</span> Liquid found in cells

The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells. It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondrion into many compartments.

<span class="mw-page-title-main">Endomembrane system</span> Membranes in the cytoplasm of a eukaryotic cell

The endomembrane system is composed of the different membranes (endomembranes) that are suspended in the cytoplasm within a eukaryotic cell. These membranes divide the cell into functional and structural compartments, or organelles. In eukaryotes the organelles of the endomembrane system include: the nuclear membrane, the endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, endosomes, and plasma (cell) membrane among others. The system is defined more accurately as the set of membranes that forms a single functional and developmental unit, either being connected directly, or exchanging material through vesicle transport. Importantly, the endomembrane system does not include the membranes of plastids or mitochondria, but might have evolved partially from the actions of the latter.

<span class="mw-page-title-main">Nuclear pore</span> Openings in nuclear envelope of eukaryotic cells

A nuclear pore is a channel as part of the nuclear pore complex (NPC), a large protein complex found in the nuclear envelope of eukaryotic cells. The nuclear envelope (NE) surrounds the cell nucleus containing DNA and facilitates the selective membrane transport of various molecules.

<span class="mw-page-title-main">Symbiogenesis</span> Evolutionary theory holding that eukaryotic organelles evolved through symbiosis with prokaryotes

Symbiogenesis is the leading evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms. The theory holds that mitochondria, plastids such as chloroplasts, and possibly other organelles of eukaryotic cells are descended from formerly free-living prokaryotes taken one inside the other in endosymbiosis. Mitochondria appear to be phylogenetically related to Rickettsiales bacteria, while chloroplasts are thought to be related to cyanobacteria.

<span class="mw-page-title-main">Cytoskeleton</span> Network of filamentous proteins that forms the internal framework of cells

The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is composed of similar proteins in the various organisms. It is composed of three main components: microfilaments, intermediate filaments, and microtubules, and these are all capable of rapid growth or disassembly depending on the cell's requirements.

A nuclear localization signalorsequence (NLS) is an amino acid sequence that 'tags' a protein for import into the cell nucleus by nuclear transport. Typically, this signal consists of one or more short sequences of positively charged lysines or arginines exposed on the protein surface. Different nuclear localized proteins may share the same NLS. An NLS has the opposite function of a nuclear export signal (NES), which targets proteins out of the nucleus.

<span class="mw-page-title-main">Intermembrane space</span>

The intermembrane space (IMS) is the space occurring between or involving two or more membranes. In cell biology, it is most commonly described as the region between the inner membrane and the outer membrane of a mitochondrion or a chloroplast. It also refers to the space between the inner and outer nuclear membranes of the nuclear envelope, but is often called the perinuclear space. The IMS of mitochondria plays a crucial role in coordinating a variety of cellular activities, such as regulation of respiration and metabolic functions. Unlike the IMS of the mitochondria, the IMS of the chloroplast does not seem to have any obvious function.

Cell physiology is the biological study of the activities that take place in a cell to keep it alive. The term physiology refers to normal functions in a living organism. Animal cells, plant cells and microorganism cells show similarities in their functions even though they vary in structure.

<span class="mw-page-title-main">Nuclear envelope</span> Nuclear membrane surrounding the nucleus in eukaryotic cells

The nuclear envelope, also known as the nuclear membrane, is made up of two lipid bilayer membranes that in eukaryotic cells surround the nucleus, which encloses the genetic material.

<span class="mw-page-title-main">Nucleoporin</span> Family of proteins that form the nuclear pore complex

Nucleoporins are a family of proteins which are the constituent building blocks of the nuclear pore complex (NPC). The nuclear pore complex is a massive structure embedded in the nuclear envelope at sites where the inner and outer nuclear membranes fuse, forming a gateway that regulates the flow of macromolecules between the cell nucleus and the cytoplasm. Nuclear pores enable the passive and facilitated transport of molecules across the nuclear envelope. Nucleoporins, a family of around 30 proteins, are the main components of the nuclear pore complex in eukaryotic cells. Nucleoporin 62 is the most abundant member of this family. Nucleoporins are able to transport molecules across the nuclear envelope at a very high rate. A single NPC is able to transport 60,000 protein molecules across the nuclear envelope every minute.

<span class="mw-page-title-main">Nucleoporin 88</span> Protein-coding gene in the species Homo sapiens

Nucleoporin 88 (Nup88) is a protein that in humans is encoded by the NUP88 gene.

<span class="mw-page-title-main">Nucleoporin 54</span> Protein-coding gene in the species Homo sapiens

Nucleoporin 54 (Nup54) is a protein that in humans is encoded by the NUP54 gene.

<span class="mw-page-title-main">Nuclear pore complex protein Nup133</span> Protein-coding gene in the species Homo sapiens

Nuclear pore complex protein Nup133, or Nucleoporin Nup133, is a protein that in humans is encoded by the NUP133 gene.

<span class="mw-page-title-main">Inner nuclear membrane protein</span> Protein embedded in inner membrane of nuclear envelope

Inner nuclear membrane proteins are membrane proteins that are embedded in or associated with the inner membrane of the nuclear envelope. There are about 60 INM proteins, most of which are poorly characterized with respect to structure and function. Among the few well-characterized INM proteins are lamin B receptor (LBR), lamina-associated polypeptide 1 (LAP1), lamina-associated polypeptide-2 (LAP2), emerin and MAN1.

<span class="mw-page-title-main">Cell membrane</span> Biological membrane that separates the interior of a cell from its outside environment

The cell membrane is a biological membrane that separates and protects the interior of a cell from the outside environment. The cell membrane consists of a lipid bilayer, made up of two layers of phospholipids with cholesterols interspersed between them, maintaining appropriate membrane fluidity at various temperatures. The membrane also contains membrane proteins, including integral proteins that span the membrane and serve as membrane transporters, and peripheral proteins that loosely attach to the outer (peripheral) side of the cell membrane, acting as enzymes to facilitate interaction with the cell's environment. Glycolipids embedded in the outer lipid layer serve a similar purpose. The cell membrane controls the movement of substances in and out of a cell, being selectively permeable to ions and organic molecules. In addition, cell membranes are involved in a variety of cellular processes such as cell adhesion, ion conductivity, and cell signalling and serve as the attachment surface for several extracellular structures, including the cell wall and the carbohydrate layer called the glycocalyx, as well as the intracellular network of protein fibers called the cytoskeleton. In the field of synthetic biology, cell membranes can be artificially reassembled.

Gene gating is a phenomenon by which transcriptionally active genes are brought next to nuclear pore complexes (NPCs) so that nascent transcripts can quickly form mature mRNA associated with export factors. Gene gating was first hypothesised by Günter Blobel in 1985. It has been shown to occur in Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster as well as mammalian model systems.

References

  1. ↑ "karyoplasm". Collins English Dictionary. Retrieved 2 December 2022.
  2. 1 2 3 4 5 6 7 8 "The human cell in nucleoplasm". Human Protein Atlas .
  3. ↑ "karyolymph". Collins English Dictionary. Retrieved 2 December 2022.
  4. ↑ Kühn, T; Ihalainen, TO; Hyväluoma, J; Dross, N; Willman, SF; Langowski, J; Vihinen-Ranta, M; Timonen, J (2011). "Protein diffusion in mammalian cell cytoplasm". PLOS ONE. 6 (8): e22962. doi: 10.1371/journal.pone.0022962 . PMC   3158749 . PMID   21886771.
  5. ↑ Harris H (1999). The Birth of the Cell . New Haven: Yale University Press. ISBN   978-0-300-07384-3.
  6. ↑ Brown R (1866). "On the Organs and Mode of Fecundation of Orchidex and Asclepiadea". Miscellaneous Botanical Works I: 511–514.
  7. ↑ "Strasburger, Eduard Adolf". Universalium. 2010. Retrieved October 31, 2022.
  8. 1 2 Kalverda, Bernike; Pickersgill, Helen; Shloma, Victor V.; Fornerod, Maarten (2010). "Nucleoporins Directly Stimulate Expression of Developmental and Cell-Cycle Genes Inside the Nucleoplasm". Cell. 140 (3): 306–383. doi: 10.1016/j.cell.2010.01.011 . PMID   20144760. S2CID   17260209.
  9. 1 2 3 4 Khan, Asmat Ullah; Qu, Rongmei; Ouyang, Jun; Dai, Jingxing (2020-04-03). "Role of Nucleoporins and Transport Receptors in Cell Differentiation". Frontiers in Physiology. 11: 239. doi: 10.3389/fphys.2020.00239 . PMC   7145948 . PMID   32308628.
  10. ↑ Hed, Greer (October 6, 2022). "What is Nucleoplasm?". wisegeek. Retrieved October 28, 2022.
  11. ↑ Casem, Merri Lynn (2016). Case Studies in Cell Biology. Elsevier. pp. 73–103. ISBN   978-0-12-801394-6.
  12. ↑ Stein; Thrall, C.L. (1973). "Evidence for the presence of nonhistone chromosomal proteins in the nucleoplasm of HeLa S3 cells". FEBS Letters. 32 (1): 41–45. doi: 10.1016/0014-5793(73)80732-X . PMID   4715686. S2CID   20285491.
  13. ↑ Houtkooper; Cantó, C.; Wanders, R.J.; Auwerx, J. (2010). "The Secret Life of NAD+: An Old Metabolite Controlling New Metabolic Signaling Pathways". Endocrine Reviews. 31 (2): 194–223. doi:10.1210/er.2009-0026. PMC   2852209 . PMID   20007326.
  14. ↑ Israelsen; Vander Heiden, M.G. (2015). "Pyruvate kinase: Function, regulation and role in cancer". Seminars in Cell & Developmental Biology. 43: 43–51. doi:10.1016/j.semcdb.2015.08.004. PMC   4662905 . PMID   26277545.
  15. ↑ Falcón; Chen, S.; Wood, M.S.; Aris, J.P. (2010). "Acetyl-coenzyme A synthetase 2 is a nuclear protein required for replicative longevity in Saccharomyces cerevisiae". Molecular and Cellular Biochemistry. 333 (1–2): 99–108. doi:10.1007/s11010-009-0209-z. PMC   3618671 . PMID   19618123.
  16. ↑ Goodsell, David (October 2009). "Molecule of the Month: Sodium-Potassium Pump". PDB-101. doi:10.2210/rcsb_pdb/mom_2009_10 . Retrieved October 30, 2022.
  17. ↑ Galva, Charitha; Artigas, Pablo; Gatto, Craig (December 2012). "Nuclear Na+/K+-ATPase plays an active role in nucleoplasmic Ca2+ homeostasis". Journal of Cell Science. 125 (24): 6137–6147. doi:10.1242/jcs.114959. PMC   3585523 . PMID   23077175.
  18. ↑ Wu, Yufei; Pegoraro, Adrian; Weitz, David; Janmey, Paul; Sun, Sean (February 2022). "The correlation between cell and nucleus size is explained by an eukaryotic cell growth model". PLOS Computational Biology. 18 (2): e1009400. doi: 10.1371/journal.pcbi.1009400 . PMC   8893647 . PMID   35180215.
  19. ↑ "The human cell in cytoplasm". Human Protein Atlas .
  20. ↑ "Nuclear Membrane". National Human Genome Research Institute .
  21. ↑ Pederson, Thoru (March 2000). "Half a Century of "The Nuclear Matrix"". Molecular Biology of the Cell. 11 (3): 799–805. doi:10.1091/mbc.11.3.799. PMC   14811 . PMID   10712500.
  22. ↑ Dechat, Thomas; Adam, Stephen A.; Taimen, Pekka; Shimi, Takeshi; Goldman, Robert D. (November 2010). "Nuclear Lamins". Cold Spring Harbor Perspectives in Biology. 2 (11): a000547. doi:10.1101/cshperspect.a000547. PMC   2964183 . PMID   20826548.
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