Why is amylose insoluble in water?
In a handout the following is stated: Amylose is insoluble in water, therefore a good storage compound e.g. in stroma of chloroplasts
This is with regard to the chemical structure of the molecule. However it has left me wondering, what is it intrinsically about the structure of a molecule that makes it soluble/insoluble in water? My thoughts at this stage are perhaps to do with whether the molecule is hydrophobic, and if that is the case - how is amylose hydrophobic?
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1 Expert Answer
Amy F. answered • 09/10/19
Tutor
5
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Experienced Physiology & Biosciences PhD
The short answer is, it's relatively nonpolar.
In it's crystallized form, hydrogen bonds form to generate a helical structure, occupying places where polarity might otherwise be able to occur in the molecule and allow it to solubilize in a polar fluid like water. Very hot water can break these bonds and force amylose into solution, but as soon as it cools enough for the amylose to recrystallize, it will precipitate again.
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Janet T.
HI, I don't agree with the statement in the handout. Amylose IS soluble, It is a twisted, helix-like structure that does not contain many hydrogen bonds. This structure caused by the 1,4 glycosidic bonds can be altered by interactions with water. The nonpolar bonds (you were right about the hydrophobic issue) can be easily broken. Celllulose is the polysaccharide most discussed as being insoluble in water. (Could there be some confusion in the reference in the handout?)07/03/19