Biochemical Tests: Proteins (OCR A Level Biology)

Revision Note

Test yourself
Alistair

Author

Alistair

Last updated

Biochemical Tests for Proteins

  • The Biuret test can be carried out quickly and easily in a lab to determine if a sample contains proteins
  • Biuret ‘reagent’ contains an alkali and copper (II) sulfate which react in the presence of peptide bonds

Apparatus

  • Test tubes
  • Test tube rack
  • Food solution
  • Control solution (containing no proteins e.g. distilled water)
  • Sodium hydroxide
  • Copper (II) sulfate solution
  • Pipette
  • White tile
  • Gloves

Method

  • Add sodium hydroxide to the food solution sample to make the solution alkaline
  • Add a few drops of copper (II) sulfate solution (which is blue)  to the sample
    • Biuret ‘reagent’ contains an alkali and copper (II) sulfate

  • Repeat steps 1 and 2 using the control solution
  • Compare the colours of the control solution and the food sample solution

Results

  • If a colour change is observed from blue to lilac/mauve, then protein is present.
    • The colour change can be very subtle, it’s wise to hold the test tubes up against a white tile when making observations

  • If no colour change is observed, no protein is present
    • For this test to work, there must be at least two peptide bonds present in any protein molecules, so if the sample contains amino acids or dipeptides, the result will be negative

The Biuret test for protein, IGCSE & GCSE Biology revision notes

A positive result from the Biuret test will produce a colour change from blue to mauve/lilac

Limitations

  • The Biuret test is qualitative - it does not give a quantitative value as to the amount of protein present in a sample
  • If the sample contains amino acids or dipeptides, the result will be negative (due to lack of peptide bonds)

You've read 0 of your 10 free revision notes

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Alistair

Author: Alistair

Expertise: Biology & Environmental Systems and Societies

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.