Editing Protein (section)

=== Abundance in cells ===

A typical [[bacteria]]l cell, e.g. ''[[Escherichia coli|E. coli]]'' and ''[[Staphylococcus aureus]]'', is estimated to contain about 2 million proteins. Smaller bacteria, such as ''[[Mycoplasma]]'' or ''[[Spirochaete|spirochetes]]'' contain fewer molecules, on the order of 50,000 to 1 million. By contrast, [[Eukaryote|eukaryotic]] cells are larger and thus contain much more protein. For instance, [[Saccharomyces cerevisiae|yeast]] cells have been estimated to contain about 50 million proteins and [[human]] cells on the order of 1 to 3 billion.<ref>{{cite journal | vauthors = Milo R | title = What is the total number of protein molecules per cell volume? A call to rethink some published values | journal = BioEssays | volume = 35 | issue = 12 | pages = 1050–1055 | date = December 2013 | pmid = 24114984 | pmc = 3910158 | doi = 10.1002/bies.201300066 }}</ref> The concentration of individual protein copies ranges from a few molecules per cell up to 20 million.<ref name="pmid22068332">{{cite journal | vauthors = Beck M, Schmidt A, Malmstroem J, Claassen M, Ori A, Szymborska A, Herzog F, Rinner O, Ellenberg J, Aebersold R | title = The quantitative proteome of a human cell line | journal = Molecular Systems Biology | volume = 7 | pages = 549 | date = November 2011 | pmid = 22068332 | pmc = 3261713 | doi = 10.1038/msb.2011.82 }}</ref> Not all genes coding proteins are expressed in most cells and their number depends on, for example, cell type and external stimuli. For instance, of the 20,000 or so proteins encoded by the human genome, only 6,000 are detected in [[lymphoblastoid]] cells.<ref>{{cite journal | vauthors = Wu L, Candille SI, Choi Y, Xie D, Jiang L, Li-Pook-Than J, Tang H, Snyder M | title = Variation and genetic control of protein abundance in humans | journal = Nature | volume = 499 | issue = 7456 | pages = 79–82 | date = July 2013 | pmid = 23676674 | pmc = 3789121 | doi = 10.1038/nature12223 | bibcode = 2013Natur.499...79W }}</ref>  The most abundant protein in nature is thought to be [[RuBisCO]], an enzyme that catalyzes the incorporation of [[carbon dioxide]] into organic matter in [[photosynthesis]].  Plants can consist of as much as 1% by weight of this enzyme.<ref>{{cite journal |doi=10.1016/0968-0004(79)90212-3 |title=The most abundant protein in the world |date=1979 |last1=Ellis |first1=R.John |journal=Trends in Biochemical Sciences |volume=4 |issue=11 |pages=241–244 }}</ref>