(a)  α-Helix is a secondary structure of proteins formed by twisting the polypeptide chain into right-handed screw-like structures. Which type of interactions is responsible for making the α -helix structure stable?

(b) Protein found in a biological system with a unique three-dimensional structure and biological activity is called a native protein. Protein denaturation occurs when a protein in its native form is subjected to a physical change like a change in temperature or a chemical change like a change in pH. Explain the cause.                                                              OR               

(a) How do you explain the presence of an aldehydic group in a glucose molecule?

(b) What are glycosidic linkages? In which type of biomolecules are they present? 

(a) α-Helix of protein show stability by forming H-bonds between amino acids of the –NH- group of one turn to the >C−O groups to the adjacent turn.

 (b) H- bonds in proteins get disturbed due to chemical and physical changes and globular and helix protein gets uncoiled. As a result, protein gets denatured and loses its biological activity.

OR

(a)   Glucose + Hydroxylamine = Monoxime.

Glucose + Hydrogen cyanide = Cyanohydrin (contains a carbonyl group which can be an aldehyde or a ketone.)

Oxidation reaction- Glucose + Bromine water = Gluconic acid (a six-carbon acid). This indicates that the carbonyl group present in glucose is an aldehydic group.

(b) Glycosidic linkage is found between two monosaccharide units through an oxygen atom joined together by an oxide linkage formed by the loss of water molecules.