The two most common examples are -helix and -sheet (fig. 1)
Proteins are not completely rigid systems and they shift between several related structures while they perform their biological functions or roles. Such changes are often induced by the binding of a substrate to the protein's active site.
The Biuret reagent is composed of potassium hydroxide (KOH), copper (II) sulphate (CuSO4) and potassium sodium tartrate (KNaC4H4O64H2O). This reagent is used in a protein assay, a colorimetric test to determine protein concentration by detecting the Cu2+ ion with the help of spectrometric methods. In the presence of proteins, this blue reagent turns purple, while when there are short-chain polypeptides in solution it turns pink [MadSci Network].
A spectrometer is an optical instrument used to measure properties of light (intensity, polarisation, etc) over a specific range of the electromagnetic spectrum (in this experiment UV-Vis at a 560nm). The independent variable is generally the wavelength of the light expressed as nanometers. These instruments are used in spectroscopy to measure the interaction between radiation and matter.
In this experiment, UV/Vis spectroscopy is used to determine the concentration of a solution of proteins with the aforementioned Biuret agent. ...