Question

KamasehGbeanquoi LO5 ChemLife - Word w View Tell me what you want to do There are other types of reagents used to determine what type of biomolecule a substance is. For example, copper ions present in Benedict's reagent reacts with the free end of any reducing sugars, such as glucose, when heated. Originally blue in color, these copper ions are reduced by the sugar, and produce an orange-red colored precipitate. Alternatively, iodine-potassium iodide (KI) may also be used when working with starch. IKI contains special tri-iodine ions which interact with the coiled structure of a starch polymer. Prior to a reaction, the IKI displays a yellow-brown color, however, after reacting with starch, a dark purple or black color is presented. The molecule pictured below produced a blue color when tested with Benedict's reagent, a yellow color when tested with IKI, and a violet color when tested with Biuret reagent. Based on the structure shown below and these chemical results, what kind of biomolecule is this?

Answer 1

Here the biomolecule is protein. Biuret test is used for detection of the peptide bonds. In presense of peptide bond it forms a violet color becuase of the cupric ion which forms a coordination complexes. It is the reaction between cupric ions of the solution with the nitrogen atoms involving in peptide bonds. Also as we are getting blue in benedict's reagent , so there is no reducing sugars. Negative results in IKI test disprove the possibility of the starch.