Section Lab Instructor Date PRELAB EXERCISE EXPERIMENT 31 Amino Acids and Protei

Question

Section Lab Instructor Date PRELAB EXERCISE EXPERIMENT 31 Amino Acids and Proteins I. While amino acids do not give positive biuret test, proteisns do. Why? 2. Provide the structure of alanine at pH 1.0 and 10.0 H,C- CH CO,H NH, Alanine pH- 1.0 pH- 100 3. Though the ninhydrin test can be conveniently carried out to detect the presence of amino acids, it cannot be used to differentiate between amino acids. Why? During the TLC analysis, care should be taken to make sure that the level of the solvent in the flask is below the spots on the filter paper. Why? 4. 451 Copyright O Houghton Miflin Company. All rights reserved

Explanation / Answer

1) Biuret is not positive for amino acids because biuret agent detect peptide bonds and that is present in proteins as amino acids are joined by peptide bond. Protein is a polypeptide and since amino acids do not have peptide bond in their structure, biuret is negative for amino acids and positive for proteins.

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