PAG 9.1 qualitative testing for proteins

Question 1

method

Answer 1

1) use the syringe to add 2cm3 distilled water to one of the test tubes
2) using the pipette and holding the tube at a 45 degree angle, carefully allow a 1cm3 Biuret reagent to slide down the side of the tube so it forms a layer at the top of the sample
3) look for any colour change where the Biuret is sitting
4) shake carefully and gently to mix
5) observe and record the colour change
6) repeat the procedure with a protein suspension instead of distilled water

Question 2

what is the chemical composition of Biuret reagent and which of these chemicals are hazardous?

Answer 2

C2H5N3O2
sodium hydroxide- corrosive and hazardous to the eyes
copper sulphate- harmful if swallowed and dangerous to the environment

Question 3

why does the procedure include making observations with the Biuret layer on top of the sample before mixing?

Answer 3

any colour change can be observed more easily and accurately

Question 4

what is the biochemical explanation for the positive result with the Biuret test?

Answer 4

Biuret reagent reacts to the peptide bonds between amino acids which make up proteins causing the sample to turn purple