In this  A-Level biology lesson  "The Biuret Test for Proteins"  You'll learn about how the biuret test for proteins is carried out (and that the biuret reagent "identifies" the peptide bonds joining polypeptides together - a reminder that long chain polypeptides have many peptide bonds!

Then we'll go through each of the 4 steps of biuret test.

Once we have those all important steps boxed off we'll go through how to describe each step when it comes to those exams.

Once again like all the other food tests (Benedict's test, Iodine test and Emulsion test) being able to describe this test (and know the expected results) is a frequently encountered question in A-level biology.

So, when you're confident you know all the steps involved and how and why this test is carried out, you’ll be ready to test your knowledge by completing the accompanying lesson booklet.

When you’ve answered all the questions, compare your answers to the ones I’ve written - where as always you’ll see exactly how to write answers in a way that gains maximum marks in the exams, laboratory reports and assignments.

A-Level biology "The Biuret Test for Proteins"

Here's a summary of the lesson: -

To test for the presence of Protein in a given sample use the Biuret test.

To 2ml of test solution add an equal volume of biuret solution. 

A blue ring forms at the surface of the solution, which disappears on shaking, and the solution turns lilac-purple, indicating protein.

The colour is due to a complex between nitrogen atoms in the peptide chain and Cu2+ ions, so this is really a test for peptide bonds.