2.Detection of proteins by biuret reaction (qualitative determination)

Question 1

composition of biuret?

Answer 1

composed of two molecules of urea

Question 2

what is the principle of the reaction of biuret?

Answer 2

in an alkaline milieu (interior), the Cu2+ ions react with peptide bonds and form a violet-colored complex

Question 3

what is the product color of the biuret reaction?

Answer 3

violet

Question 4

For producing positive biuret reaction, a compound should contain how many peptide bonds?

Answer 4

2 at least

Question 5

which materials are needed for the biuret reaction?

Answer 5

 Diluted blood plasma (10x dilution)
 NaOH solution (2.5 mol/l)
 CuSO4 solution (0.065 mol/l)
 Pasteur pipette

Question 6

which color we will observe If there is copper-II-sulphate in excess in our product in the biuret test?

Answer 6

blue coloured Cu(OH)2 precipitate will appear in the bottom of the tube after several minutes.

Question 7

what is the color of the Cu(OH)2

Answer 7

blue

Question 8

How would you detect proteins in urine

Answer 8

By sulphosalicylic acid (or nitric acid/trichloroacetic acid)

Question 9

How would you detect the polypeptides?

Answer 9

By the biuret reaction