Practical Biochemistry (2)

Practical Biochemistry (2)

1. Benedict's test + precipitation

   • Benedict's test reveals presence of reducing sugars which results in orange-red precipitate.
   • More reducing sugar present, more precipitate will be formed + more Benedict's solution will be 'used up.' If precipitate is filtered, concentration of remaining solution can be measured.
     • Tell you how much Benedict's solution has been used up - can estimate concentration of reducing sugar in original sample.

2. Comparing solutions with colorimeter

   • Colorimeter: device that shines beam of light through sample.
   • Photoelectric cell picks up light that's passed through sample - give you reading showing how much light has passed through.
   • Place solution in sample chamber between light + photoelectric cell in small clear plastic container (cuvette) in special test tube.
     • More copper sulphate used up in Benedict's test in sample, less light will be blocked out + more light will be transmitted. Means readings taken give measure of Benedict's solution.

3. Calibration - making precise measurments

   • Prepare calibration curve by taking range of known concentrations of reducing sugar.
     • Carry out Benedict's test on each one. Filter precipitate out of solution.
       • Use colorimeter to give readings of amount of light passing through solutions.
         • Plot readings in graph to show light getting through (transmission) against reducing sugar concentration.
           • Take reading from unknown sample. From graph, can read off equivalent reducing sugar concentration for new reading.
   • Using colorimeter to take readings of different samples that contain reducing sugar doesn't tell us how much reducing sugar is present - simply tells us which sample contains more.