Editing Cytosol (section)

===Water===
Most of the cytosol is  [[water]], which makes up about 70% of the total volume of a typical cell.<ref name="Luby-Phelps-2000">{{cite journal |author=Luby-Phelps K |title=Cytoarchitecture and physical properties of cytoplasm: volume, viscosity, diffusion, intracellular surface area |journal=Int. Rev. Cytol. |volume=192 |pages=189–221 |year=2000 |pmid=10553280 |doi=10.1016/S0074-7696(08)60527-6 |url=http://webusers.physics.illinois.edu/~alek/598PNM/hw/IntRevCytol.pdf |series=International Review of Cytology |isbn=978-0-12-364596-8 |url-status=dead |archive-url=https://web.archive.org/web/20110719211202/http://webusers.physics.illinois.edu/~alek/598PNM/hw/IntRevCytol.pdf |archive-date=2011-07-19 }}</ref> The [[intracellular pH|pH]] of the intracellular fluid is 7.4.<ref>{{cite journal |vauthors=Roos A, Boron WF |title=Intracellular pH |journal=Physiol. Rev. |volume=61 |issue=2 |pages=296–434 |date=April 1981 |pmid=7012859 |doi=10.1152/physrev.1981.61.2.296 }}</ref> while mouse cell cytosolic [[pH]] ranges between 7.0 and 7.4, and is usually higher if a cell is growing.<ref>{{Cite journal| pmid = 3558476| volume = 104| issue = 4| pages = 1019–1033| last1 = Bright| first1 = G R| title = Fluorescence ratio imaging microscopy: temporal and spatial measurements of cytoplasmic pH| journal = The Journal of Cell Biology| year = 1987| doi = 10.1083/jcb.104.4.1019| last2 = Fisher| first2 = GW| last3 = Rogowska| first3 = J| last4 = Taylor| first4 = DL| pmc = 2114443}}</ref> The [[viscosity]] of cytoplasm is roughly the same as pure water, although [[diffusion]] of small molecules through this liquid is about fourfold slower than in pure water, due mostly to collisions with the large numbers of [[macromolecule]]s in the cytosol.<ref name="Verkman-2002">{{cite journal |author=Verkman AS |title=Solute and macromolecule diffusion in cellular aqueous compartments |journal=Trends Biochem. Sci. |volume=27 |issue=1 |pages=27–33 |date=January 2002 |pmid=11796221 |doi=10.1016/S0968-0004(01)02003-5}}</ref> Studies in the [[brine shrimp]] have examined how water affects cell functions; these saw that a 20% reduction in the amount of water in a cell inhibits metabolism, with metabolism decreasing progressively as the cell dries out and all metabolic activity halting when the water level reaches 70% below normal.<ref name="James-1984">{{cite journal |author=Clegg James S. |author-link = James S. Clegg|title=Properties and metabolism of the aqueous cytoplasm and its boundaries |journal=Am. J. Physiol. |volume=246 |issue=2 Pt 2 |pages=R133–51 |date=1984 |pmid=6364846 |doi=10.1152/ajpregu.1984.246.2.R133 | s2cid=30351411 |doi-access=}}</ref>

Although water is vital for life, the structure of this water in the cytosol is not well understood, mostly because methods such as [[nuclear magnetic resonance spectroscopy]] only give information on the average structure of water, and cannot measure local variations at the microscopic scale. Even the structure of pure water is poorly understood, due to the ability of water to form structures such as [[water cluster]]s through [[hydrogen bond]]s.<ref name="Wiggins-1990"/>

The classic view of water in cells is that about 5% of this water is strongly bound in by solutes or macromolecules as water of [[solvation]], while the majority has the same structure as pure water.<ref name="James-1984"/> This water of solvation is not active in [[osmosis]] and may have different solvent properties, so that some dissolved molecules are excluded, while others become concentrated.<ref>{{cite journal |author=Fulton AB |title=How crowded is the cytoplasm? |journal=Cell |volume=30 |issue=2 |pages=345–7 |date=September 1982 |pmid=6754085 |doi=10.1016/0092-8674(82)90231-8|s2cid=6370250 }}</ref><ref>{{cite journal |author=Garlid KD |title=The state of water in biological systems |journal=Int. Rev. Cytol. |volume=192 |pages=281–302 |year=2000 |pmid=10553283 |doi=10.1016/S0074-7696(08)60530-6 |series=International Review of Cytology |isbn=978-0-12-364596-8}}</ref> However, others argue that the effects of the high concentrations of macromolecules in cells extend throughout the cytosol and that water in cells behaves very differently from the water in dilute solutions.<ref>{{cite journal |author=Chaplin M |title=Do we underestimate the importance of water in cell biology? |journal=Nat. Rev. Mol. Cell Biol. |volume=7 |issue=11 |pages=861–6 |date=November 2006 |pmid=16955076 |doi=10.1038/nrm2021|s2cid=42919563 }}</ref> These ideas include the proposal that cells contain zones of low and high-density water, which could have widespread effects on the structures and functions of the other parts of the cell.<ref name="Wiggins-1990">{{cite journal|author=Wiggins PM|author-link=Philippa Wiggins|date=1 December 1990|title=Role of water in some biological processes|journal=Microbiol. Rev.|volume=54|issue=4|pages=432–49|doi=10.1128/MMBR.54.4.432-449.1990|pmc=372788|pmid=2087221}}</ref><ref>{{cite journal|author=Wiggins PM|author-link=Philippa Wiggins|date=June 1996|title=High and low density water and resting, active and transformed cells|journal=Cell Biol. Int.|volume=20|issue=6|pages=429–35|doi=10.1006/cbir.1996.0054|pmid=8963257|s2cid=42866068}}</ref> However, the use of advanced nuclear magnetic resonance methods to directly measure the mobility of water in living cells contradicts this idea, as it suggests that 85% of cell water acts like that pure water, while the remainder is less mobile and probably bound to macromolecules.<ref>{{cite journal |vauthors=Persson E, Halle B |title=Cell water dynamics on multiple time scales |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=105 |issue=17 |pages=6266–71 |date=April 2008 |pmid=18436650 |pmc=2359779 |doi=10.1073/pnas.0709585105|bibcode=2008PNAS..105.6266P |doi-access=free }}</ref>