Experiment 6: Proteins Flashcards
The source of protein used for Experiment 6
Egg albumin
6.A1. Biuret Test
- Add 1 ml of albumin, then 1/2 mL of 10% NaOH. Then shake.
- Add CuSO4 drop wise.
6.A2. What was the physical result of the Biuret test?
Solution turned a violet color
6.A3. What group is responsible for Biuret test’s results?
The presence of peptide linkage in amide group (CONH)
6.A4. What is Biuret Test a good index for determining?
Biuret test is a good index for determining the extent of protein hydrolysis.
Hydrolytic products give colors ranging from violet to pink depending on extent of hydrolysis progression.
6.B1. XANTHROPROTEIC TEST
Egg albumin + HNO3 (nitric acid) + conc. NH4OH (ammonium hydroxide)
6.B2. Results of Xanthroproteic Test
Layers separated; yellow-orange solution forms
6.B3. What is the role of NH4OH in Xanthroproteic test?
It is the alkali used to neutralize the solution
6.B4. What was responsible for the formation of yellow-orange color in Xanthroproteic test?
This is due to the nitration of the benzene ring / C6H5 in amino acids
6.C1. Millon’s Test
2 ml of albumin + Hg (NO3)2 (Millon’s reagent)
6.C2. Results of Millon’s Test
Produces flesh-colored —> red precipitate
6.C3. How is Millon’s reagent made?
By dissolving Hg / mercury in HNO3 / nitric acid = Hg (NO3)2
6.C4. What causes the reaction in Millon’s test?
The phenol group (C6H5-OH) in tyrosine
6.D1. Molisch’s Test
Albumin + Molisch reagent + H2SO4
6.D2. Results of Molisch’s Test
Violet ring develops at junction of liquid layers
6.D3. What causes the reaction in Molisch’s test?
Presence of glyco-protein
6.E1. Sulfur Test
albumin + NaOH + CH3COOH
Cover above solution with filter paper covered in Pb (C2H3O2)2. Expose to heat.
6.E2. What happened to the solution? The paper dipped in Pb (C2H3O2)2 when exposed to the solution?
Black precipitates formed
The bottom of the paper turned brown
6.E3. Albumin when heated with NaOH split up the sulfur to form _____
Na2S / Sodium sulfide
6.E4. What happens when Na2S is acidified with CH3COOH and treated with Pb (C2H3O2)2?
Black precipitate or PbS / lead sulfide forms
6.E5. What makes the reaction in Sulfur Test possible?
Presence of cystine, cysteine, or methionine
6.F1. EFFECT OF HEAT IN PROTEINS
Albumin + heat in water bath
6.F2. What happens to albumin after being heated?
Albumin coagulates and the solution becomes cloudy
6.G1. HELLER’S RING TEST
Albumin + conc. HNO3
