Which among the following is a constituent of natural silk?

Question

UnlockIAS · Accepted Answer

Correct — B, Nitrogen. Natural silk is a protein fibre — it is made mainly of fibroin (the filament) with a sericin gum coating, both of which are proteins. Proteins are polymers of amino acids, and every amino acid contains nitrogen in its amino (–NH2) group. So nitrogen is an essential constituent element of silk (alongside carbon, hydrogen and oxygen).

Why the other options are wrong — (a) Phosphorus is characteristic of nucleic acids (DNA/RNA), ATP and bone, not of the fibroin/sericin proteins that make up silk.  (c) Magnesium is the central metal of chlorophyll and a plant/mineral nutrient; it is not a building block of the silk protein.  (d) Potassium is an electrolyte/mineral ion in cells and sap, not a structural element of the silk fibre.

Concept: Silk secreted by the silkworm (Bombyx mori) is a natural protein fibre. Its two proteins — fibroin (about 70-75%, the strong core filament) and sericin (the sticky coating removed during degumming) — are built from amino acids rich in glycine, alanine and serine. Because all proteins are chains of nitrogen-bearing amino acids, nitrogen is a defining chemical constituent of silk.

State PCS 2023 Q48 — Science & Technology PYQ with Answer

State PCS 2023 Q48 — Science & Technology PYQ with Answer