Question

The amino acid Tryptophan exhibits maximum UV absorption at what approximate wavelength

• A. 220 nm
• B. 260 nm
• C. 280 nm
• D. 340 nm

Hint:

Remember the key wavelengths for biomolecules: Proteins at 280 nm (due to Trp/Tyr) and Nucleic Acids at 260 nm. The A280/A260 ratio is often used to assess the purity of a protein sample.

Answer 1

The Correct Option is C

Step 1: Introduction:
Aromatic amino acids, specifically phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp), absorb ultraviolet (UV) light due to their conjugated ring systems. This is how proteins are often detected and quantified, with each amino acid exhibiting a unique absorption maximum.
Step 2: Absorption Characteristics:
UV absorption maxima for aromatic amino acids are approximately:
Phenylalanine (Phe): \(\sim\)257 nm (low absorption)
Tyrosine (Tyr): \(\sim\)274 nm
Tryptophan (Trp): \(\sim\)280 nm (highest absorption)
Tryptophan's strong absorption generally dictates the overall UV absorption of proteins. Consequently, 280 nm is the standard wavelength for protein concentration measurements using UV spectroscopy.
Other relevant wavelengths include:
220 nm: Peptide bond absorption.
260 nm: Nucleic acid (DNA and RNA) absorption maximum.
340 nm: Absorption peak for reduced coenzyme NADH.
Step 3: Conclusion:
Tryptophan shows its maximum UV absorption at roughly 280 nm.