2. What did you learn about the specificity of the biuret reagent? 3. Ninhydrin

Question

2. What did you learn about the specificity of the biuret reagent? 3. Ninhydrin reacts with a mixture of amino acids and curns purple. Could proline be one of the amino acids? How could you find out if the mixture contained proline? Several individual unknowns arc tested to determine the type of molecule present. Given the complet- ed table below, indicate whether unknowns 1 through 5 are protein, reducing sugar, starch, lipid, or free amino acids(+positive result). 4. UNKNOWN BENEDICTS LUGOL'S BIURET NINHYDRIN SUDAN IV ANSWER TEST TEST TEST TEST colorimetric reagents. Given the resules in the following positive 5. Mixtures of unknowns are tested with several table, determine which of the four choices below best describes the contents of each tube (+ result). BENEDICTS LUGOL'S BIURET NINHYDRIN SUDAN IV TEST TEST TUBE TEST TEST TEST TEST c. Tube 1: protcin and free amino acids Tube 1: reducing sugar and protein Tube 2: lipid, free amino acids, and protein Tube 3 starch, reducing sugar, and lipid a. Tube 2: lipid, reducing sugar, and protein Tube 3: lipid, reducing sugar, and stanch Tube 1: free amino acids and lipids Tube 2: lipid, starch, and free amino acids Tube 3: starch, free amino acids, and reducing sugar d. Tube 1: protein and free amino acids Tube 2: starchs, protein, and lipid Tube 3: free amino acids, starch, and protcin b. WORKSHEET

Explanation / Answer

2. The biuret reagent reacts with peptide bonds and therefore reacts with proteins but not with free amino acids.

3. Proline does react with ninhydrin. But when proline reacts with ninhydrin, it produced a yellow colour. That yellow colour can be easily covered by purple colour of mixture of other amino acids. Proline contains a nitrogen molecule in a aromatic ring structure.

To know whether mixture contains proline, we need to separate the amino acids by thin layer chromatography or paper chromatography.

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