Question

Define the following:
(i) Peptide linkage
(ii) Denatured protein

Answer 1

(i) Peptide linkage: A peptide linkage is the bond formed between the carboxyl group of one amino acid and the amino group of another amino acid, releasing a molecule of water. This bond forms the backbone of a protein.
(ii) Denatured protein: A denatured protein is a protein whose three-dimensional structure has been altered due to external factors such as heat, pH, or chemicals. This denaturation process disrupts the biological activity of the protein, although the primary structure (the sequence of amino acids) remains intact.

Answer 2

Amino acids show amphoteric behaviour because they have both acidic and basic functional groups. The carboxyl group (-COOH) behaves as an acid, donating a proton (H+) in solution, while the amino group (-NH2) behaves as a base, accepting a proton. This dual capability allows amino acids to act as both acids and bases, depending on the pH of the solution.

Answer 3

Fibrous proteins are elongated, insoluble in water, and have structural roles (e.g., collagen, keratin), while globular proteins are spherical, water-soluble, and have functional roles such as enzymes and antibodies. Fibrous proteins are typically used for mechanical support, while globular proteins are involved in metabolic processes.

Answer 4

The two different secondary structures of proteins are:
1. Alpha helix: A coiled structure where the polypeptide chain coils into a right-handed spiral, stabilized by hydrogen bonds.
2. Beta-pleated sheet: A structure where the polypeptide chains are aligned parallel or an- tiparallel, forming hydrogen bonds between adjacent strands.