- Standard curve
A

**standard curve**is a quantitative research tool, a method of plottingassay data that is used to determine theconcentration of a substance, particularlyprotein s andDNA . It can be used in many biological experimentsThe assay is first performed with various known concentrations of a substance similar to that being measured. For example a standard curve for protein concentration is often created using known concentrations of

bovine serum albumin . The assay procedure may measureabsorbance ,optical density ,luminescence ,fluorescence ,radioactivity , or something else. An assay for protein is called theBradford assay ; it is a colorimetric assay. Thereagent coomassie brilliant blue turns blue when it binds toarginine andaromatic amino acid s present in protein. The intensity of the colour is best measured at 595 nm, which is the maximumabsorbance (A_{max}) frequency of the blue dye, using aspectrophotometer . In this case the greater the absorbance, the higher the protein concentration.These data are used to make the standard curve, plotting concentration on the X axis, and assay measurement on the Y axis. The same assay is then performed with samples of unknown concentration. To analyze the data, one locates the measurement on the Y-axis that corresponds to the assay measurement of the unknown substance and follows a line to intersect the standard curve. The corresponding value on the X-axis is the concentration of substance in the unknown sample.

**ee also***

Color

*Linear regression

*Logarithmic scale

*Protein **References*** [

*http://www.histosoft.com/services/background/ba/baback.html Bradford Assay Background*] (pdf format)

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