Question

which of the following amino acids are used to measure the protein concentration by UV? A. His B. Pro C. Trp D. Phe E. Tyr

Answer 1

The amino acids used to measure protein concentration by UV are Trp, Phe, and Tyr, which are aromatic amino acids with significant UV absorbance due to their benzene ring structures. So the correct options are C, D, and E.

Step-by-step explanation:

The amino acids that are used to measure protein concentration by UV are tryptophan (Trp), phenylalanine (Phe), and tyrosine (Tyr). These are the aromatic amino acids that have significant UV absorbance due to their benzene rings which act as chromophores. Phenylalanine has the least absorption in UV, while tryptophan and tyrosine have higher absorbance and can be especially important for quantitative protein measurement.

UV spectroscopy is useful in protein studies because of the presence of these amino acids. They absorb light in the UV range and can provide information about protein content and concentration. Moreover, fluorescence spectroscopy can reveal information about protein conformation based on the blue-shift or red-shift in tyrosine and tryptophan fluorescence when they are in different environments.

Answer 2

C. Trp D. Phe E. Tyr

Step-by-step explanation:

The concentration of a protein has a direct relation with absorbance of the protein in a UV spectrophotometer. The formula which relates concentration with absorbance is described as under:

A = ∈ x c x l

where, A = Absorbance

∈ = Molar extinction co-efficient

c = Concentration of absorbing species i.e. protein

l = Path length of light

Tryptophan (Trp), phenylalanine (Phe ) and tyrosine (Tyr) are three aromatic amino acids which are used to measure protein concentration by UV. It is mainly because of tryptophan (Trp), protein absorbs at 280 nm which gives us an idea of protein concentration during UV spectroscopy.

The table depicting the wavelength at which these amino acids absorb and their respective molar extinction coefficient is as under:

Amino acid Wavelength Molar extinction co-efficient (∈)

Tryptophan 282 nm 5690

Tyrosine 274 nm 1280

Phenylalanine 257 nm 570

In view of table above, we can easily see that Molar extinction co-efficient (∈) of Tryptophan is highest amongst all these 3 amino acids that is why it dominates while measuring concentration.