Editing Glycogen (section)

==Structure==
[[File:Glycogen2.PNG|thumb|α(1→4)-glycosidic linkages in the glycogen oligomer]]
[[File:Glycogen.svg|thumb|α(1→4)-glycosidic and α(1→6)-glycosidic linkages in the glycogen oligomer]]
Glycogen is a branched [[biopolymer]] consisting of linear chains of [[glucose]] [[Residue (chemistry)|residues]] with an average chain length of approximately 8–12 glucose units and 2,000-60,000&nbsp;residues per one molecule of glycogen.<ref name="Manners1991">{{cite journal |last1=Manners |first1=David J. |year=1991 |title=Recent developments in our understanding of glycogen structure |journal=Carbohydrate Polymers |volume=16 |issue=1 |pages=37–82 |issn=0144-8617 |doi=10.1016/0144-8617(91)90071-J}}</ref><ref>{{cite book |last=Ronner |first=Peter|year=2018 |title=Netter's Essentials Biochemistry |publisher=Elsevier |isbn=978-1-929007-63-9 |location=USA |pages=254}}</ref>

Like amylopectin, glucose units are linked together linearly by α(1→4) [[glycosidic bond]]s from one glucose to the next. Branches are linked to the chains from which they are branching off by α(1→6) glycosidic bonds between the first glucose of the new branch and a glucose on the stem chain.<ref>{{cite book |last1=Berg |first1=Jeremy Mark |last2=Tymoczko |first2=John L. |last3=Stryer |first3=Lubert |year=2012 |title=Biochemistry |edition=7th |publisher=W. H. Freeman |isbn=978-1429203142 |page=[https://archive.org/details/biochemistrythed00berg/page/n375 338] |url=https://archive.org/details/biochemistrythed00berg |url-access=limited}}</ref>

Each glycogen is essentially a ball of glucose trees, with around 12 layers, centered on a [[glycogenin]] protein, with three kinds of glucose chains: A, B, and C. There is only one C-chain, attached to the glycogenin. This C-chain is formed by the self-glucosylation of the glycogenin, forming a short primer chain. From the C-chain grows out B-chains, and from B-chains branch out B- and A-chains. The B-chains have on average 2 branch points, while the A-chains are terminal, thus unbranched. On average, each chain has length 12, tightly constrained to be between 11 and 15. All A-chains reach the spherical surface of the glycogen.<ref>{{Cite journal |last1=Gunja-Smith |first1=Zeenat |last2=Marshall |first2=J.J. |last3=Mercier |first3=Christiane |last4=Smith |first4=E.E. |last5=Whelan |first5=W.J. |date=1970-12-28 |title=A revision of the Meyer-Bernfeld model of glycogen and amylopectin |journal=FEBS Letters |volume=12 |issue=2 |pages=101–104 |doi=10.1016/0014-5793(70)80573-7 |pmid=11945551 |s2cid=34722785 |issn=0014-5793 |doi-access=free|bibcode=1970FEBSL..12..101G }}</ref><ref>{{Cite journal |last1=Roach |first1=Peter J. |last2=Depaoli-Roach |first2=Anna A. |last3=Hurley |first3=Thomas D. |last4=Tagliabracci |first4=Vincent S. |date=2012-01-16 |title=Glycogen and its metabolism: some new developments and old themes |journal=Biochemical Journal |volume=441 |issue=3 |pages=763–787 |doi=10.1042/BJ20111416 |pmid=22248338 |pmc=4945249 |issn=0264-6021}}</ref>

Glycogen in muscle, liver, and fat cells is stored in a hydrated form, composed of three or four parts of water per part of glycogen associated with 0.45&nbsp;[[Molar concentration#Units|millimoles]] (18&nbsp;mg) of potassium per gram of glycogen.<ref name="pmid1615908">{{cite journal |vauthors=Kreitzman SN, Coxon AY, Szaz KF |date=July 1992 |title=Glycogen storage: Illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition |journal=[[The American Journal of Clinical Nutrition]] |volume=56 |issue=1, Suppl |pages=292s–293s |pmid=1615908 |doi=10.1093/ajcn/56.1.292S |doi-access=free}}</ref>

Glucose is an osmotic molecule, and can have profound effects on osmotic pressure in high concentrations possibly leading to cell damage or death if stored in the cell without being modified.<ref name="oclc913469736"/> Glycogen is a non-osmotic molecule, so it can be used as a solution to storing glucose in the cell without disrupting osmotic pressure.<ref name="oclc913469736"/>