Practical biochemistry 2: Quantitative tests for biological molecules

Practical biochemistry 2: Quantitative tests for biological molecules

1. Quantitaive testing for reducing sugars

   • If more sugar is present the amount of precipitate will increase
   • The amount of copper (II) ions remaining in the solution will decrease

2. Using a colorimeter

   • Use a pipette to take the supernatant and place it in a cuvette, which can be placed into the colorimeter
   • Colour filters are used for greater accuracy- shine a light through the solution and detect how much passes through (percentage transmission)
   • Little unreacted copper sulfate, the superntanat is less blue, absorption of red light is low and percentage transmission is high
   • Device is zeroed between each reading by placing a 'blank' sample to reset the transmission, the blank would be water

3. Creating a calibration curve

   • 1. Take a series of known concentrations of reducing sugar
   • 2. Using a sample of each, carry out a Benedict's test
   • 3. Use a colorimeter to read the percentage transmission of light through each
   • 4. Plot a graph to show the transmission of light against the concentration of reducing sugars. Can use with other 'unknown' samples to determine the concentration of sugar

4. Use of biosensors

   • Take a biological or chemical variable which cannot easily be measured, and convert it to an electrical signal
   • Can be used to detect contaminants in water, pathogens and toxins in food. Even be used to detect airborne bacteria in counter-bioterrorism programmes