This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Biological Function of Proteins, Subject name: Biochemistry
Substitution of which one of the following amino acids in place of alanine would increase the absorbance of protein at 280 nm - 
Select and explain. 
A. Leucine, B. Arginine, C. Tryptophan, D. Prolein
C: Tryptophan
Answer: C: Tryptophan 
Explanation: Ans. is 'c' i.e., Tryptophan Most Amino acids do not absorb visible light and are thus colourless.However aromatic aminoacids absorb ultraviolet light.This accounts for the characteristic strong absorbance of light by most proteins at a wavelength of 280 nm, a property exploited by researchers in the characterization of proteins;Tryptophan makes the major contribution to the ability of most proteins to absorb light in the region of 280 nmAlso know,Other amino acids which absorb lightTyrosinePhenylalanineMeasurement of light absorption by a spectrophotometer is used to detect and identify molecules and to measure their concentration in solution.