Editing Cytosol (section)

===Macromolecules===
Protein molecules that do not bind to [[cell membrane]]s or the [[cytoskeleton]] are dissolved in the cytosol. The amount of protein in cells is extremely high, and approaches 200&nbsp;mg/ml, occupying about 20–30% of the volume of the cytosol.<ref name="Ellis-2001">{{cite journal |author=Ellis RJ |title=Macromolecular crowding: obvious but underappreciated |journal=Trends Biochem. Sci. |volume=26 |issue=10 |pages=597–604 |date=October 2001 |pmid=11590012 |doi=10.1016/S0968-0004(01)01938-7}}</ref> However, measuring precisely how much protein is dissolved in cytosol in intact cells is difficult, since some proteins appear to be weakly associated with membranes or organelles in whole cells and are released into solution upon [[cell lysis]].<ref name="James-1984"/> Indeed, in experiments where the plasma membrane of cells were carefully disrupted using [[saponin]], without damaging the other cell membranes, only about one quarter of cell protein was released. These cells were also able to synthesize proteins if given ATP and amino acids, implying that many of the enzymes in cytosol are bound to the cytoskeleton.<ref>{{cite journal |vauthors=Hudder A, Nathanson L, Deutscher MP |title=Organization of Mammalian Cytoplasm |journal=Mol. Cell. Biol. |volume=23 |issue=24 |pages=9318–26 |date=December 2003 |pmid=14645541 |pmc=309675 |doi=10.1128/MCB.23.24.9318-9326.2003}}</ref> However, the idea that the majority of the proteins in cells are tightly bound in a network called the [[microtrabecular lattice]] is now seen as unlikely.<ref>{{cite journal |author=Heuser J |title=Whatever happened to the 'microtrabecular concept'? |journal=Biol Cell |year=2002 |volume=94 |issue=9| pages=561–96  |doi=10.1016/S0248-4900(02)00013-8 |pmid=12732437|s2cid=45792524 }}</ref>

In prokaryotes the cytosol contains the cell's [[genome]], within a structure known as a [[nucleoid]].<ref>{{cite journal |vauthors=Thanbichler M, Wang S, Shapiro L |title=The bacterial nucleoid: a highly organized and dynamic structure |journal=J Cell Biochem |volume=96 |issue=3 |pages=506–21 |year=2005 |pmid=15988757 |doi=10.1002/jcb.20519|s2cid=25355087 |doi-access=free }}</ref> This is an irregular mass of [[DNA]] and associated proteins that control the [[transcription (genetics)|transcription]] and [[DNA replication|replication]] of the bacterial [[chromosome]] and [[plasmid]]s. In eukaryotes the genome is held within the [[cell nucleus]], which is separated from the cytosol by [[nuclear pore]]s that block the free diffusion of any molecule larger than about 10&nbsp;[[nanometre]]s in diameter.<ref>{{cite book |author=Peters R |chapter=Introduction to Nucleocytoplasmic Transport |title=Xenopus Protocols |volume=322 |pages=235–58 |year=2006 |pmid=16739728 |doi=10.1007/978-1-59745-000-3_17 |series=Methods in Molecular Biology |isbn=978-1-58829-362-6}}</ref>

This high concentration of macromolecules in cytosol causes an effect called [[macromolecular crowding]], which is when the [[activity (chemistry)|effective concentration]] of other macromolecules is increased, since they have less volume to move in. This crowding effect can produce large changes in both the [[reaction rate|rates]] and the position of [[chemical equilibrium]] of reactions in the cytosol.<ref name="Ellis-2001"/> It is particularly important in its ability to alter [[dissociation constant]]s by favoring the association of macromolecules, such as when multiple proteins come together to form [[protein complex]]es, or when [[DNA-binding protein]]s bind to their targets in the [[genome]].<ref>{{cite journal |vauthors=Zhou HX, Rivas G, Minton AP |title=Macromolecular crowding and confinement: biochemical, biophysical, and potential physiological consequences |journal=[[Annu Rev Biophys]] |volume=37 |pages=375–97 |year=2008 |pmid=18573087 |doi=10.1146/annurev.biophys.37.032807.125817 |pmc=2826134}}</ref>