Q.1
The porphyrin ring (tetrapyrrole structure) is NOT found in functional
(A) chlorophyll
(B) hemoglobin
(C) hemocyanin
(D) leghemoglobin
Porphyrin Ring Tetrapyrrole Structure Not Found In: MCQ Answer & Explanation
The porphyrin ring, a tetrapyrrole structure, is absent in functional hemocyanin, making it the correct answer (C) to the question on where this key biochemical component is not present.
Correct Answer
Hemocyanin lacks the porphyrin ring (tetrapyrrole structure) used in oxygen transport by other options. This copper-based protein in mollusks and arthropods relies on dicopper centers bound to histidine residues instead.
Option Breakdown
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Chlorophyll (A): Contains a porphyrin-derived chlorin ring with central magnesium, enabling photosynthesis in plants.
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Hemoglobin (B): Features a heme prosthetic group with iron at the porphyrin ring center for oxygen binding in vertebrates.
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Hemocyanin (C): Uses copper ions without any porphyrin; oxygen binding occurs via Cu(I)/Cu(II) oxidation without tetrapyrrole.
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Leghemoglobin (D): Plant hemoglobin analog with heme (iron-porphyrin) that facilitates nitrogen fixation in legume root nodules.
Porphyrin Ring Basics
Porphyrins consist of four pyrrole rings linked by methine bridges, forming a stable aromatic tetrapyrrole that coordinates metals like Fe or Mg. This structure imparts color and function in heme proteins and chlorophyll, but hemocyanin evolved a distinct non-porphyrin mechanism.
