(a) Write the product when D-glucose reacts with conc. `HNO_(3)`.
(b) Amino acids shown amphoteric behaviour. Why ?
(c ) Write one difference between `alpha`-helix and `beta`-pleated structures of proteins.

Explanation

(a) Saccharic acid `[COOH(CHOH)_(4)COOH]` will be obtained when D-glucose reacts with conc. `HNO_(3)`.
(b) Amino acids show amphoteric behaviour due to the formation of Zwitter ion.
`H_(2)N-underset(alpha"-amino acid")(underset(R)underset(|)overset(+)(C)-)overset(O)overset(||)(C)-OH to H_(3)^(+)N-underset("Zwitter ion")(underset(R)underset(|)(C)H-)COO^(-)`
In acidic medium , `COO^(-)` ion acts as base and accepts a proton to form the cation . While in the basic medium , `overset(+)(N)H_(3)` ions loses a proton to form the anion. Hence amino acids show amphoteric behaviour.
(c) `alpha`-helix structure has intra-molecular hydrogen binding between the molecules of polypeptide chain whereas `beta`-pleated structure has inter-molecular hydrogen bonding between polypeptide chains.