Quiz 4: Carbohydrates

Biology

The raffinose is a trisaccharide which yields glucose, galactose and fructose on hydrolysis. It is a non-reducing sugar with no free aldehyde group at 1 st carbon of either glucose or galactose. The structure of raffinose is as follows: img

In DNA (deoxyribonucleic acid) molecule, the sugar molecule is deoxyribose. Its structure is as follows: img Modification of DNA sugar: In this sugar molecule, the ribose sugar is deficient of hydroxyl group at position 2 and forms 2-deoxyribose sugar. Analogous to DNA molecule sugar: There is an analogous sugar derivative glucosamine which is similar in structure to 2-deoxyribose sugar. The difference is only that 2-deoxyribose sugar has five membered ring while glucosamine has six membered ring. They are similar in that both are deficient of hydroxyl group at position 2. But glucosamine has amine group instead of hydroxyl group at position 2 and 2-deoxyribose sugar has no group at position 2. Its structure is as follows: img The sugar of DNA molecule retains some of the properties of sugars in it. These are water solubility or hydrophobic nature. The 2-deoxyribose sugar has 3 hydroxyl groups which allow it to get easily dissolve in polar solvents like water.

Glucose molecule has two ring forms which are alpha and beta. These two ring forms are in equilibrium with each other and an open ring form as follows: img The structure of alpha and beta form depends only upon the carbon 1. If it is upward, then it is beta form and if downward then alpha form. This is possible only when the carbon at position 1 is free. If we talk about a polysaccharide in which there are multiple img bond and three img bonds. This occurs as follows: img In the multiple img bonds, there is only one OH (hydroxyl group) at first position of last glucose of the chain which would be free. In case of img bond, there would be one hydroxyl group free for each bond. Thus, total 4 hydroxyl groups would be free in the mentioned structure and hence, there would be 4 structures that would exist in equilibrium.