Question

Which protein properties allow UV spectroscopy to be used as a method of determining concentration? (A) Proteins have partially planar characteristics in peptide bonds. (B) Globular proteins cause scattering of light. (C) Proteins contain aromatic groups in certain amino acids. (D) All organic macromolecules can be assessed with UV spectroscopy.

Short answer

(C) Proteins contain aromatic groups in certain amino acids.

Step-by-step solution

Understand the Question

The question is asking which property of proteins specifically allows UV spectroscopy to be used for determining their concentration.

Examine Protein Properties

Consider the given options and analyze each property in the context of UV spectroscopy.

Analyze Option (A)

Proteins having partially planar characteristics in peptide bonds is true, but it doesn't specifically relate to UV absorption.

Analyze Option (B)

Globular proteins causing scattering of light is correct, but scattering does not directly contribute to UV absorption used in concentration measurements.

Analyze Option (C)

Proteins contain aromatic groups in certain amino acids (like tryptophan, tyrosine, and phenylalanine), which are known to absorb UV light efficiently. This property is directly related to UV spectroscopy for concentration determination.

Analyze Option (D)

While many organic macromolecules can be assessed with UV spectroscopy, this statement is too broad and does not specifically explain why proteins can be measured.

Select the Correct Answer

Based on analysis, the correct answer is (C) Proteins contain aromatic groups in certain amino acids.

Key concepts

UV spectroscopy

UV spectroscopy is a powerful analytical technique. It measures the intensity of ultraviolet (UV) light absorbed by a sample.
UV light typically falls in the wavelength range of 200-400 nm.
When UV light passes through a protein solution, some of the light is absorbed.
The amount of light absorbed helps understand the concentration of the proteins.
This is based on the Beer-Lambert Law.
According to this law, the absorption of light by a substance is proportional to its concentration.
This principle is central to using UV spectroscopy for measuring protein concentration.

protein concentration measurement

Measuring protein concentration is crucial in many biological and clinical studies.
By using UV spectroscopy, you can estimate how much protein is in a sample.
This is done by measuring the absorbance at a specific wavelength.
Typically, proteins are measured at 280 nm, where aromatic amino acids absorb UV light.
The higher the absorbance at this wavelength, the higher the protein concentration.
An important factor is that the presence of other substances that also absorb at 280 nm may interfere with measurements.
Therefore, it's crucial to purify protein samples before measurement.

aromatic amino acids

Aromatic amino acids are crucial to the UV absorption properties of proteins.
The main aromatic amino acids in proteins are tryptophan, tyrosine, and phenylalanine.
These amino acids have ring structures that absorb UV light effectively.
Tryptophan and tyrosine are particularly strong absorbers at 280 nm.
Phenylalanine absorbs at shorter wavelengths, but its contribution to UV absorbance at 280 nm is minimal.
The presence and proportion of these aromatic amino acids in a protein determine its UV absorption characteristics.

tryptophan absorption

Tryptophan is one of the key aromatic amino acids responsible for UV absorbance in proteins.
Due to its high absorbance at 280 nm, it significantly impacts the measurement of protein concentration using UV spectroscopy.
Tryptophan has a high molar extinction coefficient, making it highly efficient at absorbing UV light.
Because of this, even small amounts of tryptophan can be detected, making UV spectroscopy a sensitive method for protein concentration measurement.
By comparing the amount of light absorbed by the tryptophan in the sample to standard curves, you can accurately determine protein concentration.