Which of the following natural substances contains iron (Fe) ?

Question

UnlockIAS · Accepted Answer

Correct — D, Myoglobin. Myoglobin is the oxygen-storing protein of muscle; each molecule carries a heme (haem) group whose central atom is iron (Fe). The iron binds and stores oxygen inside muscle cells, and it is this iron-heme pigment (not blood) that gives red meat its colour. The related blood protein haemoglobin also contains iron in its heme.

Why the other options are wrong — (a) Chlorophyll has the same porphyrin-ring architecture as heme, but its central metal atom is magnesium (Mg), not iron — that is why plants are green, not red.  (b) Collagen is the main structural protein of connective tissue (skin, tendon, bone matrix); it is built from amino acids (rich in glycine, proline, hydroxyproline) and contains no iron.  (c) Keratin is the structural protein of hair, nails and the skin's outer layer; it is rich in sulphur-containing cysteine but has no iron.

Concept: A favourite exam theme is 'which biomolecule holds which metal at its core'. Iron sits in the heme of haemoglobin and myoglobin (oxygen transport/storage). Magnesium sits at the centre of chlorophyll (light capture). Structural proteins such as collagen and keratin hold no metal ion — they are chains of amino acids.

State PCS 2020 Q87 — Science & Technology PYQ with Answer

State PCS 2020 Q87 — Science & Technology PYQ with Answer