Final answer:
NaCl is added to the Bradford assay to create a stable ionic environment and minimize interference from pH and ionic strength, allowing for more accurate protein concentration measurements.
Step-by-step explanation:
The reason we add NaCl to the Bradford assay is to create a standard curve for measuring protein concentration. The Bradford assay is a colorimetric protein assay, meaning it measures the amount of protein present based on the color change it causes in a dye.
In the presence of proteins, the Coomassie Brilliant Blue dye in the assay changes from red to blue. However, the dye alone can also change color in response to pH and ionic strength. By adding NaCl, we create a stable ionic environment that minimizes interference from pH and ionic strength, allowing us to more accurately measure protein concentration.