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Definitions

Definitions. *Amino Acids ( a.a ): Amino Acids are molecules containing a carboxyl group (COOH), an amino group (NH2) and a side chain (R-group) that varies between different a.a bonded to the α-carbon atom. Peptide bond:

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Definitions

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  1. Definitions *Amino Acids (a.a): Amino Acids are molecules containing a carboxyl group (COOH), an amino group (NH2) and a side chain (R-group) that varies between different a.a bonded to the α-carbon atom.

  2. Peptide bond: It is a chemical bond formed between two a.a. when the carboxyl group of one a.a. reacts with the amino group of the other a.a. *Proteins: Proteins are organic compounds made of a.a arranged in a linear chain polymer and joined together by peptide.

  3. Experiment 1 Nada AL-Mebairik

  4. Color Tests for Proteins and Amino Acids A)General Proteins Color Tests 1/BiuretTest: *It is a general test used for detecting the presence of proteins and peptides. *Protein sample treated with Copper Sulphate (CUSO4) in an alkaline solution (NaOH) formed a pink-violet colored complex.

  5. *This color is due to a reaction between Copper ions (CU++) and peptide bonds (CO-NH) in alkaline solution (at least two peptide bonds are required for a positive test). *Biuret (H2N-CO-NH-CO-NH2) react with CUSO4 in an alkaline solution and give the same color like protein, that is why the test is called Biuret test.

  6. 2/Ninhydrin Test: *a.a. (that have α-amino group) react with ninhydrin to form blue colored complex. *This color is due to librate NH3 with ninhydrin. *Ninhydrin is used to locate the α-amino acid in paper chromatography as a blue to purple spots. *Also, permits the quantitative estimation of α-amino acid and peptides in column chromatography. *Proline give yellow color due to lack of α-amino group.

  7. 3/Xanthoproteic Test: *Nitration of the aromatic rings in Tyrosine and Tryptophan, with concentrated HNO3, produce a yellow color. heat Tyrosine or Tryptophan + con.HNO3 Yellow color *Phenylalanine does not produce the color because the benzene ring is not activated for nitration.

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