Cytoplasm

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Cell biology
Animal cell diagram
Animal Cell.svg
Components of a typical animal cell:
  1. Nucleolus
  2. Nucleus
  3. Ribosome (dots as part of 5)
  4. Vesicle
  5. Rough endoplasmic reticulum
  6. Golgi apparatus (or, Golgi body)
  7. Cytoskeleton
  8. Smooth endoplasmic reticulum
  9. Mitochondrion
  10. Vacuole
  11. Cytosol (fluid that contains organelles; with which, comprises cytoplasm)
  12. Lysosome
  13. Centrosome
  14. Cell membrane

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 (a gel-like substance), the organelles (the cell's internal sub-structures), and various cytoplasmic inclusions. The cytoplasm is about 80% water and is usually colorless. [1]

Contents

The submicroscopic ground cell substance, or cytoplasmic matrix, that remains after the exclusion of the cell organelles and particles is groundplasm. It is the hyaloplasm of light microscopy, a highly complex, polyphasic system in which all resolvable cytoplasmic elements are suspended, including the larger organelles such as the ribosomes, mitochondria, plant plastids, lipid droplets, and vacuoles.

Many cellular activities take place within the cytoplasm, such as many metabolic pathways, including glycolysis, photosynthesis, and processes such as cell division. The concentrated inner area is called the endoplasm and the outer layer is called the cell cortex, or ectoplasm.

Movement of calcium ions in and out of the cytoplasm is a signaling activity for metabolic processes. [2]

In plants, movement of the cytoplasm around vacuoles is known as cytoplasmic streaming.

History

The term was introduced by Rudolf von Kölliker in 1863, originally as a synonym for protoplasm, but later it has come to mean the cell substance and organelles outside the nucleus. [3] [4]

There has been certain disagreement on the definition of cytoplasm, as some authors prefer to exclude from it some organelles, especially the vacuoles [5] and sometimes the plastids. [6]

Physical nature

It remains uncertain how the various components of the cytoplasm interact to allow movement of organelles while maintaining the cell's structure. The flow of cytoplasmic components plays an important role in many cellular functions which are dependent on the permeability of the cytoplasm. [7] An example of such function is cell signalling, a process which is dependent on the manner in which signaling molecules are allowed to diffuse across the cell. [8] While small signaling molecules like calcium ions are able to diffuse with ease, larger molecules and subcellular structures often require aid in moving through the cytoplasm. [9] The irregular dynamics of such particles have given rise to various theories on the nature of the cytoplasm.

As a sol-gel

There has long been evidence that the cytoplasm behaves like a sol-gel. [10] It is thought that the component molecules and structures of the cytoplasm behave at times like a disordered colloidal solution (sol) and at other times like an integrated network, forming a solid mass (gel). This theory thus proposes that the cytoplasm exists in distinct fluid and solid phases depending on the level of interaction between cytoplasmic components, which may explain the differential dynamics of different particles observed moving through the cytoplasm. A papers suggested that at length scale smaller than 100  nm, the cytoplasm acts like a liquid, while in a larger length scale, it acts like a gel. [11]

As a glass

It has been proposed that the cytoplasm behaves like a glass-forming liquid approaching the glass transition. [9] In this theory, the greater the concentration of cytoplasmic components, the less the cytoplasm behaves like a liquid and the more it behaves as a solid glass, freezing more significant cytoplasmic components in place (it is thought that the cell's metabolic activity can fluidize the cytoplasm to allow the movement of such more significant cytoplasmic components). [9] A cell's ability to vitrify in the absence of metabolic activity, as in dormant periods, may be beneficial as a defense strategy. A solid glass cytoplasm would freeze subcellular structures in place, preventing damage, while allowing the transmission of tiny proteins and metabolites, helping to kickstart growth upon the cell's revival from dormancy. [9]

Other perspectives

Research has examined the motion of cytoplasmic particles independent of the nature of the cytoplasm. In such an alternative approach, the aggregate random forces within the cell caused by motor proteins explain the non-Brownian motion of cytoplasmic constituents. [12]

Constituents

The three major elements of the cytoplasm are the cytosol, organelles and inclusions.

Cytosol

The cytosol is the portion of the cytoplasm not contained within membrane-bound organelles. Cytosol makes up about 70% of the cell volume and is a complex mixture of cytoskeleton filaments, dissolved molecules, and water. The cytosol's filaments include the protein filaments such as actin filaments and microtubules that make up the cytoskeleton, as well as soluble proteins and small structures such as ribosomes, proteasomes, and the mysterious vault complexes. [13] The inner, granular and more fluid portion of the cytoplasm is referred to as endoplasm.

Proteins in different cellular compartments and structures tagged with green fluorescent protein Localisations02eng.jpg
Proteins in different cellular compartments and structures tagged with green fluorescent protein

Due to this network of fibres and high concentrations of dissolved macromolecules, such as proteins, an effect called macromolecular crowding occurs and the cytosol does not act as an ideal solution. This crowding effect alters how the components of the cytosol interact with each other.

Organelles

Organelles (literally "little organs") are usually membrane-bound structures inside the cell that have specific functions. Some major organelles that are suspended in the cytosol are the mitochondria, the endoplasmic reticulum, the Golgi apparatus, vacuoles, lysosomes, and in plant cells, chloroplasts.

Cytoplasmic inclusions

The inclusions are small particles of insoluble substances suspended in the cytosol. A huge range of inclusions exist in different cell types, and range from crystals of calcium oxalate or silicon dioxide in plants, [14] [15] to granules of energy-storage materials such as starch, [16] glycogen, [17] or polyhydroxybutyrate. [18] A particularly widespread example are lipid droplets, which are spherical droplets composed of lipids and proteins that are used in both prokaryotes and eukaryotes as a way of storing lipids such as fatty acids and sterols. [19] Lipid droplets make up much of the volume of adipocytes, which are specialized lipid-storage cells, but they are also found in a range of other cell types.

Controversy and research

The cytoplasm, mitochondria, and most organelles are contributions to the cell from the maternal gamete. Contrary to the older information that disregards any notion of the cytoplasm being active, new research has shown it to be in control of movement and flow of nutrients in and out of the cell by viscoplastic behavior and a measure of the reciprocal rate of bond breakage within the cytoplasmic network. [20]

The material properties of the cytoplasm remain an ongoing investigation. A method of determining the mechanical behaviour of living cell mammalian cytoplasm with the aid of optical tweezers has been described. [21]

See also

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">Biological membrane</span> Enclosing or separating membrane in organisms acting as selective semi-permeable barrier

A biological membrane, biomembrane or cell membrane is a selectively permeable membrane that separates the interior of a cell from the external environment or creates intracellular compartments by serving as a boundary between one part of the cell and another. Biological membranes, in the form of eukaryotic cell membranes, consist of a phospholipid bilayer with embedded, integral and peripheral proteins used in communication and transportation of chemicals and ions. The bulk of lipids in a cell membrane provides a fluid matrix for proteins to rotate and laterally diffuse for physiological functioning. Proteins are adapted to high membrane fluidity environment of the lipid bilayer with the presence of an annular lipid shell, consisting of lipid molecules bound tightly to the surface of integral membrane proteins. The cell membranes are different from the isolating tissues formed by layers of cells, such as mucous membranes, basement membranes, and serous membranes.

<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">Endoplasmic reticulum</span> Cell organelle that synthesizes, folds and processes proteins

The endoplasmic reticulum (ER) is a part of a transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum (RER), and smooth endoplasmic reticulum (SER). The endoplasmic reticulum is found in most eukaryotic cells and forms an interconnected network of flattened, membrane-enclosed sacs known as cisternae, and tubular structures in the SER. The membranes of the ER are continuous with the outer nuclear membrane. The endoplasmic reticulum is not found in red blood cells, or spermatozoa.

<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">Lysosome</span> Cell membrane organelle

A lysosome is a single membrane-bound organelle found in many animal cells. They are spherical vesicles that contain hydrolytic enzymes that digest many kinds of biomolecules. A lysosome has a specific composition, of both its membrane proteins and its lumenal proteins. The lumen's pH (~4.5–5.0) is optimal for the enzymes involved in hydrolysis, analogous to the activity of the stomach. Besides degradation of polymers, the lysosome is involved in cell processes of secretion, plasma membrane repair, apoptosis, cell signaling, and energy metabolism.

<span class="mw-page-title-main">Peroxisome</span> Type of organelle

A peroxisome (IPA:[pɛɜˈɹɒksɪˌsoʊm]) is a membrane-bound organelle, a type of microbody, found in the cytoplasm of virtually all eukaryotic cells. Peroxisomes are oxidative organelles. Frequently, molecular oxygen serves as a co-substrate, from which hydrogen peroxide (H2O2) is then formed. Peroxisomes owe their name to hydrogen peroxide generating and scavenging activities. They perform key roles in lipid metabolism and the reduction of reactive oxygen species.

<span class="mw-page-title-main">Vacuole</span> Membrane-bound organelle in cells containing fluid

A vacuole is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes in solution, though in certain cases they may contain solids which have been engulfed. Vacuoles are formed by the fusion of multiple membrane vesicles and are effectively just larger forms of these. The organelle has no basic shape or size; its structure varies according to the requirements of the cell.

<span class="mw-page-title-main">Vesicle (biology and chemistry)</span> Any small, fluid-filled, spherical organelle enclosed by a membrane

In cell biology, a vesicle is a structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer. Vesicles form naturally during the processes of secretion (exocytosis), uptake (endocytosis), and the transport of materials within the plasma membrane. Alternatively, they may be prepared artificially, in which case they are called liposomes. If there is only one phospholipid bilayer, the vesicles are called unilamellar liposomes; otherwise they are called multilamellar liposomes. The membrane enclosing the vesicle is also a lamellar phase, similar to that of the plasma membrane, and intracellular vesicles can fuse with the plasma membrane to release their contents outside the cell. Vesicles can also fuse with other organelles within the cell. A vesicle released from the cell is known as an extracellular vesicle.

<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.

Protoplasm is the part of a cell that is surrounded by a plasma membrane. It is a mixture of small molecules such as ions, monosaccharides, amino acids, and macromolecules such as proteins, polysaccharides, lipids, etc.

<span class="mw-page-title-main">Nucleoplasm</span> Protoplasm that permeates a cells nucleus

The nucleoplasm, also known as karyoplasm, 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. 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. The structures suspended in the nucleoplasm include chromosomes, various proteins, nuclear bodies, the nucleolus, nucleoporins, nucleotides, and nuclear speckles.

<span class="mw-page-title-main">Autophagy</span> Process of cells digesting parts of themselves

Autophagy is the natural, conserved degradation of the cell that removes unnecessary or dysfunctional components through a lysosome-dependent regulated mechanism. It allows the orderly degradation and recycling of cellular components. Although initially characterized as a primordial degradation pathway induced to protect against starvation, it has become increasingly clear that autophagy also plays a major role in the homeostasis of non-starved cells. Defects in autophagy have been linked to various human diseases, including neurodegeneration and cancer, and interest in modulating autophagy as a potential treatment for these diseases has grown rapidly.

<span class="mw-page-title-main">Cytoplasmic streaming</span> Flow of the cytoplasm inside the cell

Cytoplasmic streaming, also called protoplasmic streaming and cyclosis, is the flow of the cytoplasm inside the cell, driven by forces from the cytoskeleton. It is likely that its function is, at least in part, to speed up the transport of molecules and organelles around the cell. It is usually observed in large plant and animal cells, greater than approximately 0.1 mm. In smaller cells, the diffusion of molecules is more rapid, but diffusion slows as the size of the cell increases, so larger cells may need cytoplasmic streaming for efficient function.

<span class="mw-page-title-main">Endoplasm</span> Also known as entoplasm

Endoplasm generally refers to the inner, dense part of a cell's cytoplasm. This is opposed to the ectoplasm which is the outer (non-granulated) layer of the cytoplasm, which is typically watery and immediately adjacent to the plasma membrane. The nucleus is separated from the endoplasm by the nuclear envelope. The different makeups/viscosities of the endoplasm and ectoplasm contribute to the amoeba's locomotion through the formation of a pseudopod. However, other types of cells have cytoplasm divided into endo- and ectoplasm. The endoplasm, along with its granules, contains water, nucleic acids, amino acids, carbohydrates, inorganic ions, lipids, enzymes, and other molecular compounds. It is the site of most cellular processes as it houses the organelles that make up the endomembrane system, as well as those that stand alone. The endoplasm is necessary for most metabolic activities, including cell division.

A bacterium, despite its simplicity, contains a well-developed cell structure which is responsible for some of its unique biological structures and pathogenicity. Many structural features are unique to bacteria and are not found among archaea or eukaryotes. Because of the simplicity of bacteria relative to larger organisms and the ease with which they can be manipulated experimentally, the cell structure of bacteria has been well studied, revealing many biochemical principles that have been subsequently applied to other organisms.

<span class="mw-page-title-main">Outline of cell biology</span> Overview of and topical guide to cell biology

The following outline is provided as an overview of and topical guide to cell biology:

<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.

<span class="mw-page-title-main">Intracellular transport</span> Directed movement of vesicles and substances within a cell

Intracellular transport is the movement of vesicles and substances within a cell. Intracellular transport is required for maintaining homeostasis within the cell by responding to physiological signals. Proteins synthesized in the cytosol are distributed to their respective organelles, according to their specific amino acid’s sorting sequence. Eukaryotic cells transport packets of components to particular intracellular locations by attaching them to molecular motors that haul them along microtubules and actin filaments. Since intracellular transport heavily relies on microtubules for movement, the components of the cytoskeleton play a vital role in trafficking vesicles between organelles and the plasma membrane by providing mechanical support. Through this pathway, it is possible to facilitate the movement of essential molecules such as membrane‐bounded vesicles and organelles, mRNA, and chromosomes.

<span class="mw-page-title-main">Biomolecular condensate</span> Class of membrane-less organelles within biological cells

In biochemistry, biomolecular condensates are a class of membrane-less organelles and organelle subdomains, which carry out specialized functions within the cell. Unlike many organelles, biomolecular condensate composition is not controlled by a bounding membrane. Instead, condensates can form and maintain organization through a range of different processes, the most well-known of which is phase separation of proteins, RNA and other biopolymers into either colloidal emulsions, gels, liquid crystals, solid crystals or aggregates within cells.

References

  1. ↑ Shepherd VA (2006). The cytomatrix as a cooperative system of macromolecular and water networks. Current Topics in Developmental Biology. Vol. 75. pp. 171–223. doi:10.1016/S0070-2153(06)75006-2. ISBN   9780121531751. PMID   16984813.
  2. ↑ Hogan CM (2010). "Calcium". In Jorgensen A, Cleveland C (eds.). Encyclopedia of Earth. National Council for Science and the Environment. Archived from the original on 12 June 2012.
  3. ↑ von Kölliker R (1863). "4. Auflage". Handbuch der Gewebelehre des Menschen. Leipzig: Wilhelm Engelmann.
  4. ↑ Bynum WF, Browne EJ, Porter R (1981). Dictionary of the history of science. Princeton University Press. ISBN   9781400853410.{{cite book}}: CS1 maint: location missing publisher (link)
  5. ↑ Parker J (1972). "Protoplasmic resistance to water deficits". In Kozlowski TT (ed.). Water deficits and plant growth, Vol. III. Plant responses and control of water balance. New York: Academic Press. pp. 125–176. ISBN   9780323153010.
  6. ↑ Strasburger E (1882). "Ueber den Theilungsvorgang der Zellkerne und das Verhältnis der Kernteilung zur Zellteilung". Arch Mikr Anat. 21: 476–590. doi:10.1007/BF02952628. hdl: 2027/hvd.32044106199177 . S2CID   85233009. Archived from the original on 27 August 2017.
  7. ↑ Cowan AE, Moraru II, Schaff JC, Slepchenko BM, Loew LM (2012). "Spatial Modeling of Cell Signaling Networks". Computational Methods in Cell Biology. Vol. 110. pp. 195–221. doi:10.1016/B978-0-12-388403-9.00008-4. ISBN   9780123884039. PMC   3519356 . PMID   22482950.
  8. ↑ Holcman D, Korenbrot JI (April 2004). "Longitudinal diffusion in retinal rod and cone outer segment cytoplasm: the consequence of cell structure". Biophysical Journal. 86 (4): 2566–82. Bibcode:2004BpJ....86.2566H. doi:10.1016/S0006-3495(04)74312-X. PMC   1304104 . PMID   15041693.
  9. 1 2 3 4 Parry BR, Surovtsev IV, Cabeen MT, O'Hern CS, Dufresne ER, Jacobs-Wagner C (January 2014). "The bacterial cytoplasm has glass-like properties and is fluidized by metabolic activity". Cell. 156 (1–2): 183–94. Bibcode:2014APS..MARJ16002P. doi:10.1016/j.cell.2013.11.028. PMC   3956598 . PMID   24361104.
  10. ↑ Taylor CV (1923). "The contractile vacuole in Euplotes: An example of the sol-gel reversibility of cytoplasm". Journal of Experimental Zoology. 37 (3): 259–289. Bibcode:1923JEZ....37..259T. doi:10.1002/jez.1400370302.
  11. ↑ Kwapiszewska, Karina; et al. (31 July 2020). "Nanoscale Viscosity of Cytoplasm Is Conserved in Human Cell Lines". The Journal of Physical Chemistry Letters . 11 (16): 6914–6920. doi: 10.1021/acs.jpclett.0c01748 . PMC   7450658 . PMID   32787203.
  12. ↑ Guo M, Ehrlicher AJ, Jensen MH, Renz M, Moore JR, Goldman RD, Lippincott-Schwartz J, Mackintosh FC, Weitz DA (August 2014). "Probing the stochastic, motor-driven properties of the cytoplasm using force spectrum microscopy". Cell. 158 (4): 822–832. doi:10.1016/j.cell.2014.06.051. PMC   4183065 . PMID   25126787.
  13. ↑ van Zon A, Mossink MH, Scheper RJ, Sonneveld P, Wiemer EA (September 2003). "The vault complex". Cellular and Molecular Life Sciences. 60 (9): 1828–37. doi:10.1007/s00018-003-3030-y. PMC   11138885 . PMID   14523546. S2CID   21196262.
  14. ↑ Prychid, Christina J.; Rudall, Paula J. (1999). "Calcium Oxalate Crystals in Monocotyledons: A Review of their Structure and Systematics" (PDF). Annals of Botany. 84 (6): 725–739. doi: 10.1006/anbo.1999.0975 .
  15. ↑ Prychid CJ, Rudall PJ (2004). "Systematics and Biology of Silica Bodies in Monocotyledons". The Botanical Review. 69 (4): 377–440. doi:10.1663/0006-8101(2004)069[0377:SABOSB]2.0.CO;2. JSTOR   4354467. S2CID   24520433.
  16. ↑ Ball SG, Morell MK (2003). "From bacterial glycogen to starch: understanding the biogenesis of the plant starch granule". Annual Review of Plant Biology. 54: 207–233. doi:10.1146/annurev.arplant.54.031902.134927. PMID   14502990.
  17. ↑ Shearer J, Graham TE (April 2002). "New perspectives on the storage and organization of muscle glycogen". Canadian Journal of Applied Physiology. 27 (2): 179–203. doi:10.1139/h02-012. PMID   12179957.
  18. ↑ Anderson AJ, Dawes EA (December 1990). "Occurrence, metabolism, metabolic role, and industrial uses of bacterial polyhydroxyalkanoates". Microbiological Reviews. 54 (4): 450–472. doi:10.1128/MMBR.54.4.450-472.1990. PMC   372789 . PMID   2087222.
  19. ↑ Murphy DJ (September 2001). "The biogenesis and functions of lipid bodies in animals, plants and microorganisms". Progress in Lipid Research. 40 (5): 325–438. doi:10.1016/S0163-7827(01)00013-3. PMID   11470496.
  20. ↑ Feneberg W, Westphal M, Sackmann E (August 2001). "Dictyostelium cells' cytoplasm as an active viscoplastic body". European Biophysics Journal. 30 (4): 284–94. doi:10.1007/s002490100135. PMID   11548131. S2CID   9782043.
  21. ↑ Hu J, Jafari S, Han Y, Grodzinsky AJ, Cai S, Guo M (September 2017). "Size- and speed-dependent mechanical behavior in living mammalian cytoplasm". Proc. Natl. Acad. Sci. U.S.A. 114 (36): 9529–9534. Bibcode:2017PNAS..114.9529H. doi: 10.1073/pnas.1702488114 . PMC   5594647 . PMID   28827333.
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