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Cell biology
The animal cell
Animal Cell.svg
Components of a typical animal cell:
  1. Nucleolus
  2. Nucleus
  3. Ribosome (little dots)
  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)
  12. Lysosome
  13. Centrosome
  14. Cell membrane

The cytoplasm comprises cytosol (the gel-like substance enclosed within the cell membrane) – and the organelles – the cell's internal sub-structures. All of the contents of the cells of prokaryote organisms (such as bacteria, which lack a cell nucleus) are contained within the cytoplasm. Within the cells of eukaryote organisms the contents of the cell nucleus are separated from the cytoplasm, and are then called the nucleoplasm. The cytoplasm is about 80% water and usually colorless.[1]

It is within the cytoplasm that most cellular activities occur, such as many metabolic pathways including glycolysis, and processes such as cell division. The concentrated inner area is called the endoplasm and the outer layer is called the cell cortex or the ectoplasm.

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

In plants, movements of the cytoplasm around vacuoles are known as cytoplasmic streaming.

Physical nature of cytoplasm[edit]

The physical nature of the cytoplasm has been contested in recent years. It remains uncertain how the varied components of the cytoplasm interact to allow movement of particles and 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.[3] An obvious 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.[4] 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.[5] The irregular dynamics of such particles have given rise to various theories on the nature of the cytoplasm.

Cytoplasm as a sol-gel[edit]

There has long been evidence that the cytoplasm behaves like a sol-gel.[6] 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.

Cytoplasm as a glass[edit]

Recently is has been proposed that the cytoplasm behaves like a glass-forming liquid approaching the glass transition.[7] 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 larger cytoplasmic components in place (it is thought that the cell's metabolic activity is able to fluidize the cytoplasm to allow the movement of such larger cytoplasmic components).[8] A cell's ability to vitrifiy in the absence of metabolic activity, as in dormant periods, may be beneficial as a defence strategy. A solid glass cytoplasm would freeze subcellular structures in place, preventing damage, while allowing the transmission of very small proteins and metabolites, helping to kickstart growth upon the cell's revival from dormancy.[9]

Other perspectives[edit]

There has been research examining 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.[10]

Constituents[edit]

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

Cytosol[edit]

Main article: 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 composed of water, salts and organic molecules.[11]

The cytosol is a complex mixture of cytoskeleton filaments, dissolved molecules, and water that fills much of the volume of a cell. The cytosol's mixture of 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.[12] 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

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[edit]

Main article: Organelles

Organelles (literally "little organs"), are usually membrane-bound, and are 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[edit]

Main article: Cytoplasmic inclusion

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,[13][14] to granules of energy-storage materials such as starch,[15] glycogen,[16] or polyhydroxybutyrate.[17] 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.[18] 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[edit]

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.[19]

The material properties of the cytoplasm remain an ongoing investigation. Recent measurements using force spectrum microscopy reveal that the cytoplasm can be likened to an elastic solid, rather than a viscoelastic fluid.

See also[edit]

References[edit]

  1. ^ Franklin Institute (November 23, 2013). "Cytoplasm". fi.edu. 
  2. ^ C. Michael Hogan. 2010. Calcium. eds. A.Jorgensen, C. Cleveland. Encyclopedia of Earth. National Council for Science and the Environment.
  3. ^ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3519356/
  4. ^ http://www.sciencedirect.com/science/article/pii/S000634950474312X
  5. ^ http://www.cell.com/abstract/S0092-8674%2813%2901479-7
  6. ^ http://onlinelibrary.wiley.com/doi/10.1002/jez.1400370302/abstract
  7. ^ http://www.cell.com/abstract/S0092-8674%2813%2901479-7
  8. ^ http://www.cell.com/abstract/S0092-8674%2813%2901479-7
  9. ^ http://www.cell.com/abstract/S0092-8674%2813%2901479-7
  10. ^ http://www.cell.com/abstract/S0092-8674%2814%2900924-6
  11. ^ Cytoplasm Composition. menloschool.org
  12. ^ van Zon A, Mossink MH, Scheper RJ, Sonneveld P, Wiemer EA (September 2003). "The vault complex". Cell. Mol. Life Sci. 60 (9): 1828–37. doi:10.1007/s00018-003-3030-y. PMID 14523546. 
  13. ^ Prychid, Christina J.; Rudall, Paula J. (1999). "Calcium Oxalate Crystals in Monocotyledons: A Review of their Structure and Systematics". Annals of Botany 84 (6): 725. doi:10.1006/anbo.1999.0975. 
  14. ^ Prychid, C. J.; Rudall, P. J.; Gregory, M. (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. 
  15. ^ Ball SG, Morell MK (2003). "From bacterial glycogen to starch: understanding the biogenesis of the plant starch granule". Annu Rev Plant Biol 54: 207–33. doi:10.1146/annurev.arplant.54.031902.134927. PMID 14502990. 
  16. ^ Shearer J, Graham TE (April 2002). "New perspectives on the storage and organization of muscle glycogen". Can J Appl Physiol 27 (2): 179–203. doi:10.1139/h02-012. PMID 12179957. 
  17. ^ Anderson AJ, Dawes EA (1 December 1990). "Occurrence, metabolism, metabolic role, and industrial uses of bacterial polyhydroxyalkanoates". Microbiol. Rev. 54 (4): 450–72. PMC 372789. PMID 2087222. 
  18. ^ Murphy DJ (September 2001). "The biogenesis and functions of lipid bodies in animals, growth and microorganisms". Prog. Lipid Res. 40 (5): 325–438. doi:10.1016/S0163-7827(01)00013-3. PMID 11470496. 
  19. ^ Feneberg, Wolfgang; Sackmann, Erich, Westphal, Monika (2001). "Dictyostelium cells' cytoplasm as an active viscoplastic body". European Biophysics Journal 30 (4): 284–94. doi:10.1007/s002490100135. PMID 11548131. 

External links[edit]


Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Cytoplasm — Please support Wikipedia.
This page uses Creative Commons Licensed content from Wikipedia. A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.

2201 news items

Science Now

Science Now
Mon, 30 Mar 2015 15:41:15 -0700

In 2001, it stopped physicians from squirting cytoplasm, which contains mitochondria, from a healthy woman's egg into the egg of a woman who had been unable to conceive. But before FDA stepped in, 17 babies were born, most healthy, but not all.

io9

io9
Mon, 30 Mar 2015 13:37:30 -0700

By accessing a cell's cytoplasm directly, the researchers were able to efficiently reprogram it. And because the nanoneedles are made from biodegradable silicon, they can be left in the body and not leave a toxic residue; they dissolve in about two ...

Medical Xpress

Medical Xpress
Mon, 30 Mar 2015 11:56:15 -0700

BHPI spurs a number of events in the cell, including the opening of calcium channels in the endoplasmic reticulum, a special intracellular compartment. The influx of calcium into the cytoplasm sets off a cascade of events that prepare the cell to deal ...

Discovery Institute

Discovery Institute
Mon, 30 Mar 2015 05:00:00 -0700

Indeed, the proteins generated by pri-miR transcripts also have the ability to promote transcription, ensuring that these proteins stay in the cytoplasm. So add a gene-regulation function to these pri-miR sequences. The article concludes: The ...

Nature.com

Nature.com
Wed, 25 Mar 2015 11:00:00 -0700

Next, transporter proteins export the excised sequences to the cytoplasm, where they are further processed before becoming competent to guide the RNA-induced silencing complex (RISC) in repressing target genes through either cleavage or translational ...

Nature.com

Nature.com
Fri, 27 Mar 2015 03:30:00 -0700

Association with AMOT proteins sequesters YAP in the cytoplasm and also promotes its ubiquitylation and its phosphorylation by Lats, on serine residue 127. This phosphorylation promotes a stable association of YAP with 14-3-3 and thus its retention in ...

Nature.com

Nature.com
Tue, 24 Mar 2015 23:22:30 -0700

SOX2 was constitutively expressed in the cytoplasm of peripheral neutrophils from both mice and humans. To examine the role of SOX2 in neutrophils, the authors generated mice with a conditional deletion of Sox2 in these cells. These mice were more ...
 
BioOptics World
Mon, 23 Mar 2015 07:51:57 -0700

These mRNAs then migrate from the nucleus into the cytoplasm and attach to structures called ribosomes. That's where translation, the second step in protein synthesis, occurs: the mRNAs attached to ribosomes function as templates on which proteins are ...
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