Chemical Forums
Specialty Chemistry Forums => Biochemistry and Chemical Biology Forum => Topic started by: AhmedEzatAlzawalaty on December 23, 2007, 01:52:59 PM
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Glycogen is muscle starch and it has alpha 1,4 and alpha 1,6 exactly like starch so why glycogen is water soluble while starch is not?
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If you are considering water solubility differences between the two polymers the main thing you need to look at is how the different structures affect the overall entropy of the solution. Starch exists in general as an alpha helix while glycogen is a highly branched random structure. In the helical conformation there are less exposed -OH groups to the solution making the starch more hydrophobic than the glycogen, the end result is that the entropy of the solution is decreased because there are less free water molecules, water molecules form a shell around hydrophobic molecules most easily seen when you look at a miscle of oil floating in water. Starch is soluble in hot water because the entropy decrease is nullified by the change in enthalpy, from the change in internal energy and PV work caused by the increase in vapor pressure(although this is fairly negligable). Glycogen, having more -OH groups exposed to the solution, has more free water molecules and a higher entropy allowing it to be soluble in water a lower temperatures. Let me know if this clears it up for you. Take some time to visualize the two polymers and convince yourself of the entropy consideration. This kind of entropy consideration is one of the main contributing factors in the behavior of most biomolecules in solution.
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thats really helpful but can u refer some links to me related to this issue?
thank u lol
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http://www.cmmp.ucl.ac.uk/people/finney/hi.html (http://www.cmmp.ucl.ac.uk/people/finney/hi.html)
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is this hypothesis als related to color produced with iodine blue for starch and red for glycogen ?or there is another explanation for color produced?
thank you
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The color is related to the production of conjugated double bonds.
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could you explain me more about the role of iodine in formation of such conjugated double bond system?
thank u
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there is a plethora of information on the iodine starch complex on the net. why don't you try to find out for yourself...if you have trouble understanding a particular explanation post the link and I'm sure there will be plenty of assisstance.