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The following points highlight the top three properties of carbohydrates in cell membrane of mammals.
1. The mammalian cell membrane contains about 5 per cent carbohydrates present in glycoproteins and glycolipids.
2. Glycophorin, the major integral membrane glycoprotein of human erythrocytes, consists of 130 amino acid residues and spans the lipid membrane having free polypeptide proteins outside both the external and internal (cytoplasmic) surfaces. Carbohydrate chains are only attached to the N-terminal portion outside the external surface.
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3. In composition of bacterial cell wall, there is presence of N-acetyl glucosamine and N-acetylgalactosamine by β(1-4) linkage. Lysozyme breaks this linkage and protects the eye.
Benedict’s test is preferred than the Fehling’s test for the detection of glucose in urine due to the following causes:
Benedict’s Qualitative solution is composed of copper sulphate, sodium citrate and sodium carbonate.
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Fehling’s solution is composed of copper sulphate, sodium potassium tartrate, and potassium hydroxide.
(i) Benedict’s test is less likely to give weakly positive results with concentrated urine due to the action of creatinine and uric acid.
(ii) It is more sensitive to small quantities of glucose because of the weaker alkali it contains.
(iii) The strong alkali (KOH) of Fehling’s solution can polymerize small quantities of glucose when vigorously boiled.
