Which method is used to determine total protein concentration using dye binding?

• A. Optical
• B. Precipitation
• C. Dye binding
• D. Colorimetric

Answer: (C)

Dye binding is the method used to determine total protein concentration by converting protein amount into a measurable color change. In this approach, a dye such as Coomassie Brilliant Blue binds to the protein molecules. When the dye binds, its color shifts (for the Bradford assay, the dye changes from reddish to blue), and the intensity of that blue color increases with more protein. A spectrophotometer measures this color change as absorbance, which is then related to protein concentration through a standard curve made with known protein standards. This approach is specific to how much protein is present because the dye-protein interaction produces a signal that grows with protein amount, making it a straightforward and widely used way to quantify total protein. Other options describe broader or different concepts (optical measurements in general, precipitating proteins, or colorimetric methods that don’t rely on dye binding), but the dye-binding strategy is the one that directly links dye interaction to protein quantity.