cytoplasm

The protoplasm outside the nucleus of a cell.

That portion of living cells bordered externally by the plasma membrane (cell membrane) and internally by the nuclear envelope. In the terminology of classical cytology, the substance in living cells and in living organisms not compartmentalized into cells was called protoplasm. It was assumed at the time that the protoplasm of various cells was similar in structure and chemistry. Results of research on cell chemistry and ultrastructure after about 1960 showed that each cell type had a recognizably different “protoplasm.” Primarily for that reason, the term protoplasm gradually fell into disuse in contemporary biology. The terms cytoplasm and nucleoplasm have been retained and are used descriptively; they are used almost synonymously with the terms cytosome (body of cytoplasm) and nucleus, respectively.

Many cells, especially the single-celled organisms or protistans, have regional cytoplasmic differentiation. The outer region is the cortex or ectoplasm, and the inner region is the endoplasm. In many cases the cortical layer is a gel made up of a meshwork of cytoskeletal fibers.

Cytoplasm contains mostly water, from 80 to 97% in different cells, except for spores and other inactive forms of living material, in which water may be present in lesser amounts. The dry mass of cells consists mainly of macromolecules: proteins, carbohydrates, nucleic acids, and lipids associated with membranes. The small molecules present in cells are mainly metabolites or metabolic intermediates. The principal ions other than the hydrogen and hydroxyl ions of water are the cations of potassium, sodium, magnesium, and calcium, and the anions chloride and bicarbonate. Many other elements are present in cytoplasm in smaller amounts. Iron is found in cytochrome pigments in mitochondria; magnesium is present in chlorophyll in chloroplasts; copper, zinc, iodine, bromine, and several other elements are present in trace quantities. See also Cytochemistry.

Sedimentation of cells by centrifugation shows that organelles and inclusions can be separated from the ground cytoplasm, the fluid phase of the cytoplasm in which they are suspended. The ground cytoplasm in turn has been shown to consist of a cytoskeletal network and the cytosol, the fluid in which the cytoskeleton is bathed. The cytoskeleton consists of several biopolymers of wide distribution in cells. Microtubules have been observed in electron micrographs of a vast number of different cell types. They consist of the protein tubulin, and are frequently covered by a fuzzy layer of microtubule-associated proteins. See also Cytoskeleton.

In most cells the smaller particles exhibit Brownian motion due to thermal agitation. In some cells lacking extensive cytoskeletal structure, particles can be moved freely around the cell by Brownian motion. In others they are restricted by their surrounding cytoskeletal elements. Particles of various types may also undergo saltatory motions which carry them farther than Brownian motion possibly could. Such excursions result from the interaction of a particle with an element of the cytoskeleton such as one or more microtubules or microfilaments. See also Cell (biology).

For more information on cytoplasm, visit Britannica.com.

That part of a cell inside the cell surface membrane, but outside the nucleus. It consists of a watery fluid, the cytosol, in which cell organelles are suspended.

The material within a biological cell that is not contained in the nucleus or other organelles.

The protoplasm of a cell surrounding the nucleus (nucleoplasm).

Schematic showing the cytoplasm, with major components of a typical animal cell (organelles):
(1) nucleolus
(2) nucleus
(3) ribosomes (little dots)
(4) vesicle
(5) rough endoplasmic reticulum (ER)
(6) Golgi apparatus
(7) Cytoskeleton
(8) smooth ER
(9) mitochondria
(10) vacuole
(11) cytoplasm
(12) lysosome
(13) centrioles within centrosome

The cytoplasm is the part of a cell that is enclosed within the plasma membrane. In eukaryotic cells, the cytoplasm contains organelles, such as mitochondria, which are filled with liquid that is kept separate from the rest of the cytoplasm by biological membranes. The cytoplasm is the site where most cellular activities occur, such as many metabolic pathways like glycolysis, and processes such as cell division. The inner, granular mass is called the endoplasm and the outer, clear and glassy layer is called the cell cortex or the ectoplasm.

The part of the cytoplasm that is not held within organelles is called the cytosol. The cytosol is a complex mixture of cytoskeleton filaments, dissolved molecules, and water that fills much of the volume of a cell. The cytosol is a gel, with a network of fibers dispersed through water. Due to this network of pores 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.

Contents 1 Constituents 1.1 Cytosol 1.2 Organelles 1.3 Cytoplasmic inclusions 2 Notes 3 Further reading 4 External links

Constituents

The cytoplasm has three major elements; the cytosol, organelles and inclusions.

Cytosol

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

The cytosol is the portion of a cell that is not enclosed within membrane-bound organelles. The cytosol is a translucent fluid in which the other cytoplasmic elements are suspended. Cytosol makes up about 70 % of the cell volume and is composed of water, salts and organic molecules.^[1] The cytoplasm also contains the protein filaments that make up the cytoskeleton, as well as soluble proteins and large structures such as ribosomes, proteasomes, and the mysterious vault complexes.^[2] The inner, granular and more fluid portion of the cytoplasm is referred to as endoplasm.

Organelles

Organelles are membrane-bound compartments within the cell that have specific functions. Some major organelles that are suspended in the cytosol are the mitochondria, the endoplasmic reticulum, the Golgi apparatus, 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,^[3][4] to granules of energy-storage materials such as starch,^[5] glycogen,^[6] or polyhydroxybutyrate.^[7] 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.^[8] 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.

Notes

1. ^ Cytoplasm Composition
2. ^ 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. 
3. ^ 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, http://aob.oxfordjournals.org/cgi/content/abstract/84/6/725 
4. ^ Prychid, C. J.; Rudall, P. J.; Gregory, M. (2003), "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, http://www.bioone.org/perlserv/?request=get-abstract 
5. ^ 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. 
6. ^ Shearer J, Graham TE (April 2002). "New perspectives on the storage and organization of muscle glycogen". Can J Appl Physiol 27 (2): 179–203. PMID 12179957. 
7. ^ Anderson AJ, Dawes EA (01 December 1990). "Occurrence, metabolism, metabolic role, and industrial uses of bacterial polyhydroxyalkanoates". Microbiol. Rev. 54 (4): 450–72. PMID 2087222. PMC: 372789. http://mmbr.asm.org/cgi/pmidlookup?view=long&pmid=2087222. 
8. ^ Murphy DJ (September 2001). "The biogenesis and functions of lipid bodies in animals, plants and microorganisms". Prog. Lipid Res. 40 (5): 325–438. doi:10.1016/S0163-7827(01)00013-3. PMID 11470496. 

Further reading

• Alberts, Bruce et al. (2003). Essential Cell Biology, 2nd ed., Garland Science, 2003, ISBN 081533480X.
• Human Anatomy & Physiology, seventh edition By; Elain N Marieb and Latja Hoehn.

External links

• What is cytoplasm? - by Genevieve Theirs -2002
• Luby-Phelps K. Cytoarchitecture and physical properties of cytoplasm: volume, viscosity, diffusion, intracellular surface area. Int Rev Cytol. 2000;192:189-221.

v • d • e Structures of the cell Endomembrane system Cell membrane - Nucleus (and Nucleolus) - Endoplasmic reticulum - Golgi apparatus - Peroxisome - Parenthesome Vesicles (Lysosome - Endosome - Phagosome - Vacuole) Cytoplasmic granules (Melanosome - Microbody - Glyoxysome - Weibel-Palade body) Endosymbionts Mitochondrion - Plastids (Chloroplast - Chromoplast - Leucoplast) Cytoskeleton Microfilaments - Intermediate filaments - Microtubules - Prokaryotic cytoskeleton External Cell wall - Cilium/Flagellum - Acrosome Other Cytoplasm - Ribosome - MTOCs (Centrosome/Centriole - Basal body - Spindle pole body) - Vault - Proteasome

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