Chapter 14: Biomolecules

The name given to the class of enzymes which catalyse redox reactions is known as enzyme oxidoreductases. An example is Alcohol Dehydrogenase, which helps in reducing alcohol levels in the human body when alcohol is ingested.

During the curdling of milk, which is caused due to bacteria, the sugar present in milk lactose is converted to lactic acid.

When glucose is treated with acetic anhydride (CH3CO)2O, in the presence of ZnCl2, it undergoes acetylation to form glucose pentaacetate, which confirms the presence of five –OH groups.

The given compound is glucose pentaacetate. Glucose contains a free –C=O group, and the formation of oxime from glucose confirms the presence of a free carbonyl group. The given compound does not have a free carbonyl group and thus does not form an oxime on reaction with hydroxylamine.

Vitamin C is a water-soluble vitamin, and hence the excess is excreted regularly from the body. Since it cannot be stored in the body, vitamin C must be supplied regularly in the diet.

Sucrose is dextrorotatory in its aqueous solution and rotates plane-polarized light entering the solution 66.5° to the right. When sucrose is hydrolysed with dilute acids or invertase enzyme, it gives two products in equimolar concentration, dextrorotatory D-(+)-glucose and laevorotatory D-(-)-fructose. Thus, hydrolysis of sucrose brings about a change in the sign of rotation, from Dextro (+) to laevo (–). So the hydrolysed mixture is laevorotatory.

An amino acid contains an –NH2 group as well as –COOH. In an aqueous solution of the amino acid, the –COOH group loses a proton [H]+ and the –NH2 gains a proton to form a zwitterion which is a salt.

The hydroxyl group of glycine is linked to the amine group of alanine by peptide (-CONH) linkage to form glycylalanine.

The amino acid residues of proteins are joined by hydrogen bonds and various other intermolecular forces. On physical or chemical change, the hydrogen bonds are disturbed, and native protein unfolds. This process is called denaturation, where secondary and tertiary structures are destroyed, but the primary structure remains intact.

Mainly the enzymes are biocatalysts which provide an alternative path to reduce the reaction activation energy. Using the enzyme sucrase, the hydrolysis of sucrose is much faster than conventional acidic hydrolysis.