Biology – Testing for biological molecules | e-Consult
Testing for biological molecules (1 questions)
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Reducing sugars contain a free aldehyde or ketone group. This functional group allows them to be oxidized, reducing other substances like copper(II) ions in Fehling's solution to copper(I) ions, resulting in a colour change.
Non-reducing sugars do not have a free aldehyde or ketone group. Instead, the glycosidic bond (the bond linking the monosaccharide units) prevents the molecule from readily forming an open aldehyde or ketone. Therefore, they cannot directly undergo oxidation to reduce Fehling's solution.
The glycosidic bond in non-reducing sugars is a beta(1→4) or beta(1→6) linkage, which is stable and does not easily reverse to form an open-chain aldehyde or ketone.