OBJECTIVE LIFE SCIENCE
BIOCHEMISTRY
Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Yellow
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Red
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Blue
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Green
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Detailed explanation-1: -For hydroxyproline and proline, a yellow colour is obtained. For asparagine, brown colour is obtained. If no colour change is observed, the analyte does not contain amino acids, amines, or ammonia.
Detailed explanation-2: -Proline gives a yellow colour because it is a secondary amine. Most amino acids are primary amines with the general structure H2NCHRCOOH . Except for proline and hydroxyproline, all the -amino acids are oxidized by ninhydrin to give the same intensely colored purple anion.
Detailed explanation-3: -Imino acids, e.g. proline and hydroxyproline, react with ninhydrin to give a yellow color. At higher temperatures (" 100°C), the yellow compound (X) is trans-formed to the purple-red compound (XI) 1°. Neuberg 11, a contemporary of Ruhemann, showed that primary amines give Ruhemann’s Purple on reaction with ninhydrin.
Detailed explanation-4: -Xanthoproteic Test In this reaction, the aromatic rings become nitrated. When nitric acid is added to a sample and the mixture is heated, a yellow solution will result if the sample contains tyrosine or tryptophan.
Detailed explanation-5: -Additionally, proline is the only amino acid that does not form a red-purple colour when developed by spraying with ninhydrin for uses in chromatography. Proline, instead, produces an orange-yellow colour.