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Imagine you somehow got a cup of pure cytosol. What would be its consistency? That is, how thick, how sticky, and how viscous would it be?

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  • $\begingroup$ pure cytosol - you just want the aqueous phase of the cytosol only? so wouldn't it have to be pretty much like water with some salt in it? the really sticky stuff is in vesicles and/or it would be excluded from the aqueous phase with whatever filtration you apply. the cell as a whole, however, does not behave like salty water, but rather like a gel $\endgroup$
    – dblyons
    Feb 4, 2017 at 0:10

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Cytosol is actually about as viscous as water (i.e. ~1 cP or 1 mPa/s).

From the Introduction of Bicknese et al. 1993

In fibroblasts and several types of epithelial cells, fluid-phase viscosity was 1.1-1.5 cP, not much higher than that of water (1 cP) (Periasamy et al., 1992). Recent measurements of cytoplasmic viscosity in CV1 and PtK1 cells by a novel ratiometric method supported the conclusion that fluid-phase viscosity in bulk cytoplasm is similar to that of water (Luby-Phelps et al., 1993).

And from the conclusion:

Apparent fluid-phase viscosity near the cell plasma membrane was 1.1 ± 0.2 cP (fibroblast) and 1.0 ± 0.2 cP (MDCK), not significantly different from the viscosity measured in bulk cytoplasm far from the plasma membrane.

Interestingly, the paper cites the following studies:

In fibroblasts, fluid-phase viscosity was weakly temperature-dependent (Arrhenius activation energy 3-5 kcal/mol) and nearly independent of cell volume (Fushimi and Verkman, 1991).


Note:

cP = centipoise

  • A centipoise (cP) is a non-SI (non-System International) measurement unit of dynamic viscosity in the centimeter gram second (CGS) system of units. It is multiple of the CGS base viscosity unit named poise (P)

  • 1 cP = 0.01 g/cm/s

  • 1 cP = 1 mPa/s

Source:

Bicknese S., N. Periasamy, S. B. Shohet, and A. S. Verkman. 1993. Cytoplasmic Viscosity Near the Cell Plasma Membrane: Measurement by Evanescent Field Frequency-Domain Microfluorimetry. Biophysical Journal 65: 1272:1282


Further Reading:

  1. Beals et al 1999

  2. Gyurov & Token 2011

  3. Guthrie & Nettesheim 2012

  4. Kalwarczyk 2011

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  • $\begingroup$ I can't comment about the consistency of this viscosity between all cell types or between taxa. I welcome suggestions to edit if anyone finds additional or more recent info. $\endgroup$ Feb 3, 2017 at 21:11
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    $\begingroup$ Nice answer - I'm not an expert in plant physiology but that's one example where I might expect to see a higher viscosity, at least in some plant tissues (I don't mean that as a criticism of your answer but just a suggestion in case no one comes along to add on). $\endgroup$
    – Bryan Krause
    Feb 3, 2017 at 21:49
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    $\begingroup$ I do not agree, all your other sources report (slightly) higher viscosities. Based on those measurements I'd say it's more comparible with blood (3-4 cP). Still fluid, just a bit less than water. However, that's only for small molecules. If you're looking at bigger probes (>5 nm) the viscosity is 20-40 cP, comparable to vegetable oil (numbers according to your Kalwarczyk source). Also, based on the protein content alone you'd also have to assume a viscosity of 5-15 cP. $\endgroup$
    – VonBeche
    Feb 4, 2017 at 23:10

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