Editing Cytoplasm (section)

==Physical nature==
It remains uncertain how the various components of the cytoplasm interact to allow movement of [[organelle]]s while maintaining the cell's structure. The flow of cytoplasmic components plays an important role in many cellular functions which are dependent on the [[Semipermeable membrane|permeability]] of the cytoplasm.<ref>{{Cite book |title=Computational Methods in Cell Biology |vauthors=Cowan AE, Moraru II, Schaff JC, Slepchenko BM, Loew LM |year=2012 |isbn=9780123884039 |volume=110 |pages=195–221 |chapter=Spatial Modeling of Cell Signaling Networks |doi=10.1016/B978-0-12-388403-9.00008-4 |pmc=3519356 |pmid=22482950}}</ref> 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.<ref>{{Cite journal |vauthors=Holcman D, Korenbrot JI |date=April 2004 |title=Longitudinal diffusion in retinal rod and cone outer segment cytoplasm: the consequence of cell structure |journal=Biophysical Journal |volume=86 |issue=4 |pages=2566–82 |bibcode=2004BpJ....86.2566H |doi=10.1016/S0006-3495(04)74312-X |pmc=1304104 |pmid=15041693}}</ref> 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.<ref name="autogenerated1">{{Cite journal |vauthors=Parry BR, Surovtsev IV, Cabeen MT, O'Hern CS, Dufresne ER, Jacobs-Wagner C |date=January 2014 |title=The bacterial cytoplasm has glass-like properties and is fluidized by metabolic activity |journal=Cell |volume=156 |issue=1–2 |pages=183–94 |bibcode=2014APS..MARJ16002P |doi=10.1016/j.cell.2013.11.028 |pmc=3956598 |pmid=24361104}}</ref> 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]].<ref>{{Cite journal |vauthors=Taylor CV |year=1923 |title=The contractile vacuole in Euplotes: An example of the sol-gel reversibility of cytoplasm |journal=Journal of Experimental Zoology |volume=37 |issue=3 |pages=259–289 |bibcode=1923JEZ....37..259T |doi=10.1002/jez.1400370302}}</ref> 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&nbsp;[[nanometer|nm]], the cytoplasm acts like a liquid, while in a larger length scale, it acts like a gel.<ref>{{Cite journal |last=Kwapiszewska |first=Karina |last2=Szczepański |first2=Krzysztof |display-authors=1 |date=31 July 2020 |title=Nanoscale Viscosity of Cytoplasm Is Conserved in Human Cell Lines |journal=[[The Journal of Physical Chemistry Letters]] |volume=11 |issue=16 |pages=6914–6920 |doi=10.1021/acs.jpclett.0c01748 |pmc=7450658 |pmid=32787203 |doi-access=free}}</ref>

===As a glass===

It has been proposed that the cytoplasm behaves like a [[glass]]-forming liquid approaching the [[glass transition]].<ref name="autogenerated1" /> 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).<ref name="autogenerated1" /> 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]].<ref name="autogenerated1" />

===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.<ref>{{Cite journal |vauthors=Guo M, Ehrlicher AJ, Jensen MH, Renz M, Moore JR, Goldman RD, Lippincott-Schwartz J, Mackintosh FC, Weitz DA |date=August 2014 |title=Probing the stochastic, motor-driven properties of the cytoplasm using force spectrum microscopy |journal=Cell |volume=158 |issue=4 |pages=822–832 |doi=10.1016/j.cell.2014.06.051 |pmc=4183065 |pmid=25126787}}</ref>