19. Which one of the following pairs of precursor amino acid and alkaloid is correct?
(1) ‘Ornithine aspartate – nicotine’ and ‘tryptophan – quinine’.
(2) ‘Ornithine – nicotine’ and ‘ tyrosine – orphine’
(3) ‘Tyrosine – quinine ‘ and ‘tryptophan- orphine’
(4) ‘Ornithine – quinine’ and ‘ ornithine aspartate – nicotine’
Correct answer: (1) ‘Ornithine aspartate – nicotine’ and ‘tryptophan – quinine’.
Explanation:
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Nicotine is a well-known alkaloid derived biosynthetically from the amino acids ornithine and aspartate, which provide the nitrogen atoms in its structure.
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Quinine, the anti-malarial alkaloid from Cinchona tree, is derived from the amino acid tryptophan.
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The other combinations are incorrect:
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Tyrosine is precursor for alkaloids such as morphine and epinephrine, not quinine.
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Ornithine is not a precursor for quinine.
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Morphine comes primarily from tyrosine, not tryptophan or ornithine.
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Option-wise:
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(1) Correct.
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(2) Incorrect: tyrosine – morphine, not ‘orphine’; also ornithine – nicotine correct, but overall false because of ‘orphine’.
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(3) Incorrect: tyrosine – quinine false; tryptophan – morphine false.
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(4) Incorrect: ornithine – quinine false.
Nicotine biosynthesis involves ornithine and aspartate as nitrogen sources, while quinine biosynthesis stems from tryptophan, illustrating the diverse amino acid origins of important alkaloid secondary metabolites with pharmaceutical significance.
