Question:easy
Light of 250 nm wavelength is absorbed by which amino acid?
Light of 250 nm wavelength is absorbed by which amino acid?
Show Hint
Look for the aromatic amino acid among the options.
Updated On: Jun 24, 2026
- Arginine
- Alanine
- Tyrosine
- Histidine
Show Solution
The Correct Option is C
Solution and Explanation
Step 1: UV absorption near 250 to 280 nm is a hallmark of an aromatic (benzene-type) ring, so the question is really asking which listed amino acid carries such a ring.
Step 2: The three aromatic amino acids are phenylalanine, tyrosine and tryptophan. Scanning the choices, only tyrosine belongs to this group, so it is the absorber at 250 nm.
Step 3: This property underpins the measurement of protein content at 280 nm; tryptophan absorbs most strongly, tyrosine next, and phenylalanine least, but all three contribute to a protein UV signal.
Step 4: Alanine has a simple methyl side chain, arginine has a guanidino group, and histidine has an imidazole ring that does not give strong absorption in this band, so none of them is the answer.
\[\boxed{\text{Tyrosine}}\]
Step 2: The three aromatic amino acids are phenylalanine, tyrosine and tryptophan. Scanning the choices, only tyrosine belongs to this group, so it is the absorber at 250 nm.
Step 3: This property underpins the measurement of protein content at 280 nm; tryptophan absorbs most strongly, tyrosine next, and phenylalanine least, but all three contribute to a protein UV signal.
Step 4: Alanine has a simple methyl side chain, arginine has a guanidino group, and histidine has an imidazole ring that does not give strong absorption in this band, so none of them is the answer.
\[\boxed{\text{Tyrosine}}\]
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