How many of the given compounds will give a positive Biuret test?

Glycine, Glycylalanine, Tripeptide, Biuret

Question

How many of the given compounds will give a positive Biuret test?

Glycine, Glycylalanine, Tripeptide, Biuret

Canvas Classes · Accepted Answer

Biuret test principle:

Biuret test gives a violet/purple colour with Cu²⁺ in alkaline solution when there are at least two peptide bonds (–CO–NH–) in the molecule.

Evaluating each compound:

| Compound | Peptide bonds | Biuret test |
|---|---|---|
| Glycine | 0 (single amino acid) | Negative |
| Glycylalanine | 1 (dipeptide) | Negative (needs ≥ 2) |
| Tripeptide | 2 | Positive ✓ |
| Biuret (H₂N–CO–NH–CO–NH₂) | 2 (–CO–NH– groups) | Positive ✓ |

Note: Biuret itself (the compound) gives a positi

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