Question

the biuret reagent, like the benedicts reagent, is blue in color due to the presence of copper ions (cu2+). the chemical reaction, unlike benedicts, does not require heating. the indicator detects the presence of proteins, which are chains of amino acids linked by special bonds called peptide bonds. the blue - colored copper ii ion can form a complex with the peptide bonds since the peptide has unshared electron pairs in nitrogen and oxygen of water. once this complex has been formed, the solution turns from blue to purple. the deeper the purple color, the higher is the number of peptide - copper complexes. 4. a solution containing hundreds of individual amino acids will test negative with biuret while a solution with only a dozen or so protein molecules will test positive. a protein is made of amino acids, so why does the biuret detect (turn positive) the protein solution but not the amino acid solution? 5. draw three different amino acids bonded by peptide bonds. why are proteins sometimes referred to as polypeptides?

Explanation:

4.

The Biuret reagent detects peptide - bonds. Amino acids alone lack peptide bonds. Proteins have peptide bonds formed by linking amino acids, so the reagent reacts with proteins but not with individual amino acids.

Peptide bonds link amino acids together. When multiple amino acids are linked by peptide bonds, they form a polypeptide chain. Proteins are made up of one or more polypeptide chains, so they are sometimes called polypeptides.

Answer:

The Biuret reagent detects peptide bonds. Individual amino acids do not have peptide bonds, while proteins do, so the reagent gives a positive result for proteins and a negative result for amino - acid solutions.

5.