Question

Which of the following contain P-1,4 linkage?
A) Maltose
B) Sucrose
C) Lactose
D) Fructose

Answer 1

Hint: The 1,4 linkage is found only in disaccharide like sucrose, maltose, etc. The beta type glycosidic linkage is the glycosidic linkage where the OH group is above the plane like in lactose.

Complete answer: Carbohydrates can be monosaccharides, disaccharides or oligosaccharides. The monomers are compounds like glucose, fructose and galactose. The disaccharides are two monomers linked with alpha or beta linkages. The bond between the two sugars in disaccharides or oligosaccharides is called a glycosidic bond. It is formed due to the condensation reactions between groups in sugar. This reaction eliminates water as a product when glycosidic linkages are formed. The 1,4 linkage is the glycosidic bond between the carbon 4 of one monomer and the first carbon of another monomer sugar. This type of bond can be of two types: alpha and beta. Beta 1,4 linkage is formed when the \[-OH\] on the carbon is not on the same plane or is below the glucose ring. Thus, the beta 1,4-glycosidic bond is formed in disaccharide such as lactose. Lactose is a disaccharide of two galactose and glucose. It has beta 1,4-glycosidic linkages. The glucose and fructose monomers do not have any glycosidic bonds in them. Maltose is a disaccharide made of two glucose units and an alpha 1,4 glycosidic bond is seen. Sucrose is a disaccharide made up of glucose and fructose with both alpha and beta linkages.
Hence, the correct answer is option C.

Note: The beta linkage is different from alpha linkage but most carbon atoms involved are fourth carbon from one and first carbon from another. It is only found in disaccharides and not in monosaccharides. The alpha or beta structure can easily be differentiated.