Amino Acids

AMINO ACIDS

Amino acids are monomers for proteins . Protein molecules are composed of a large number of amino acids joined together by peptide bonds . There are 20 naturally occurring amino acids each of which contains an amino group (-NH2 , a carboxyl group (-COOH , a hydrogen (-H ) and a variable group (designated as -R . A peptide bond is formed when the carboxyl group of one amino acid bonds with the amino group of other amino acid to form a primary protein structure . This chain of amino acids , joined by peptide bonds , forms a

secondary protein structure by coiling into an alpha (a ) helix or into a beta (b ) pleated sheets . A tertiary protein structure results when this alpha helix or beta pleated sheet folds back on itself . Two or more proteins join together to form a quaternary protein structure

BIURET TEST

Biuret test is basically a test for the peptide bonds that link individual amino acids into a protein chain . Biuret reagent is a two part system . Dilute copper sulphate (CuSO4 ) forms the first part and a strong alkaline solution of potassium hydroxide (KOH ) as the second part . KOH is used for denaturing the protein and breaking its hydrogen or other weak covalent bonds . If peptides or proteins are present , Cu 2 ions from the Biuret reagent combine with the peptide bonds . The resulting solution acquires a violet color whose tone depends on the amount of protein present . If the peptides are absent in the test solution , then the solution retains the blue color of the Cu 2 ions in the reagent

In the testing conditions , certain controls are also employed . A known chemical , which does not contain the testes substance (protein in this case , is used as the negative control . Distilled water is used as negative control in the Biuret test . Another known chemical , which surely contains the tested substance (i .e . protein in this test , is used as positive control . Serum albumin can be used as a positive control for the testing of peptides . The color change between the positive and negative control solutions is used for comparison with substance whose composition is unknown

MATERIALS REQUIRED- test tubes , pipette , control solutions- distilled water and serum albumin solution , dilute CuSO4 solution , KOH solution and the test solution

METHOD-

Prepare the control solution

In three different test tubes , take the test solution , the negative control- distilled water and the positive control- the albumin solution .Note the original colors of each of the three solutions

In each test tube , add about 5 drops of dilute CuSO4 solution and tap the side of the test tube slightly with the finger to mix the contents

After about 15- 20 seconds , add about 10 drops of KOH solution to each test tube and tap slightly to mix

Record the colors of each solution

RESULT : - The negative control distilled water will retain the light blue color of the dilute CuSO4 solution . The positive control solution of albumin will show a very deep violet color . The...