# Quantitative Determination of Protein Concentration Using the Biuret Test

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Pang Mei Chen

Practical 1 Post Lab Questions

Quantitative Determination of Protein Concentration Using The Biuret Test

F1                [pic 1]

Figure 1 : Standard curve of absorbance against protein concentration for solutions of known protein content.

Q4         The line on the graph should be a line of best fit. It is because it best represents the correlation ABS and concentration of known protein on the graph.

Q5        Yes. Divide the absorbance value by a number that provides an outcome that is within the range of the standard curve. Dilute the protein solution value by a few times and add buffer solution to add up to the volume of solution to get into the range of the standard curve. Plot the absorbance value to get the value of final protein concentration.

Q6

• Dilute the protein concentration from the “sun” and “shade” suspension by decreasing the volume of protein solution and add buffer solution to fit the standard curve to find the value ofabsorbance.
• Concentrate the protein concentration which is lower in absorbance value to fit into the standard curve of protein concentration.

Divide the absorbance value by a number that provides an outcome that is within the range of the standard curve. Dilute the protein solution value by a few times and add buffer solution to add up to the volume of solution to get into the range of the standard curve. Plot the absorbance value to get the value of final protein concentration.

Pang Mei Chen

Q7        Yes. The “Sun” suspension contains more rubisco than the ”shade” suspension as the “sun” suspension has a higher absorbance value than the “shade” suspension.

Q8

• Protein suspension looks darker than predicted due to high concentration of protein in test tubes.
• Protein suspension looks paler than predicted because the spectrometer is set at the wrong wavelength.
• There is no changes in colour in any one of the test tubes due to presence of a copper chelating agent.

Q9

• There is presence of reducing agent in the buffer that makes the protein suspension turn dark violet.
• The intensity of sunlight at different areas affect the production of rubisco in plants. Therefore, if the intensity of sunlight is high, more rubisco will be produced.
• There is presence of lipoprotein in the sample of protein suspension which cause the intensity of the colour of protein suspension to be higher.

Q10        The protein concentration in protein derived from the leaves is too concentrated that the absorbance value is not within the range of the standard curve. Students have to dilute the protein sample to find the concentration of protein in the sample.

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