Editing Glucose (section)

===Biosynthesis===
{{main|Gluconeogenesis|Glycogenolysis}}
In plants and some [[prokaryote]]s, glucose is a product of [[photosynthesis]].<ref name="photo">{{Cite web|url=http://www.rsc.org/Education/Teachers/Resources/cfb/Photosynthesis.htm|title=Chemistry for Biologists: Photosynthesis|website=www.rsc.org|access-date=5 February 2018|url-status=live|archive-url=https://web.archive.org/web/20160804060610/http://www.rsc.org/Education/Teachers/Resources/cfb/Photosynthesis.htm|archive-date=4 August 2016}}</ref> Glucose is also formed by the breakdown of polymeric forms of glucose like [[glycogen]] (in animals and [[mushroom]]s) or starch (in plants). The cleavage of glycogen is termed glycogenolysis, the cleavage of starch is called starch degradation.<ref>{{cite journal |last1= Smith, Alison M. |last2=Zeeman, Samuel C. |last3= Smith, Steven M. |year= 2005 |title= Starch Degradation |journal= Annu. Rev. Plant Biol. |volume= 56 |issue=1 |pages= 73–98 |doi= 10.1146/annurev.arplant.56.032604.144257 |pmid=15862090 |bibcode=2005AnRPB..56...73S }}</ref>

The metabolic pathway that begins with molecules containing two to four carbon atoms (C) and ends in the glucose molecule containing six carbon atoms is called gluconeogenesis and occurs in all living organisms. The smaller starting materials are the result of other metabolic pathways. Ultimately almost all [[biomolecule]]s come from the assimilation of carbon dioxide in plants and microbes during photosynthesis.<ref name=Voet/>{{rp|359}} The free energy of formation of α-{{sm|d}}-glucose is 917.2 kilojoules per mole.<ref name=Voet/>{{rp|59}} In humans, gluconeogenesis occurs in the liver and kidney,<ref name="Szablewski">Leszek Szablewski: ''Glucose Homeostasis and Insulin Resistance''. Bentham Science Publishers, 2011, {{ISBN|978-1-608-05189-2}}, p.&nbsp;46.</ref> but also in other cell types. In the liver about {{cvt|150|g}} of glycogen are stored, in skeletal muscle about {{cvt|250|g}}.<ref name="Löffler/Petrides 389">Peter C. Heinrich: ''Löffler/Petrides Biochemie und Pathobiochemie'' {{In lang|de}}. Springer-Verlag, 2014, {{ISBN|978-3-642-17972-3}}, p.&nbsp;389.</ref> However, the glucose released in muscle cells upon cleavage of the glycogen can not be delivered to the circulation because glucose is phosphorylated by the hexokinase, and a glucose-6-phosphatase is not expressed to remove the phosphate group. Unlike for glucose, there is no transport protein for [[Glucose-6-phosphate dehydrogenase (coenzyme-F420)|glucose-6-phosphate]]. Gluconeogenesis allows the organism to build up glucose from other metabolites, including [[lactic acid|lactate]] or certain [[amino acid]]s, while consuming energy. The renal [[tubular cell]]s can also produce glucose.

Glucose also can be found outside of living organisms in the ambient environment. Glucose concentrations in the atmosphere are detected via collection of samples by aircraft and are known to vary from location to location. For example, glucose concentrations in atmospheric air from inland China range from 0.8 to 20.1 pg/L, whereas east coastal China glucose concentrations range from 10.3 to 142 pg/L.<ref>{{cite journal |last1=Wang |first1=Gehui |last2=Kawamura |first2=Kimitaka |last3=Hatakeyama |first3=Shiro |last4=Takami |first4=Akinori |last5=Li |first5=Hong |last6=Wang |first6=Wei |title=Aircraft Measurement of Organic Aerosols over China |journal=Environmental Science & Technology |date=May 2007 |volume=41 |issue=9 |pages=3115–3120 |doi=10.1021/es062601h |pmid=17539513 |bibcode=2007EnST...41.3115W }}</ref>