Experiment 7 - COLOR REACTIONS OF PROTEINS

Question 1

The word “protein” is derived from the Greek word “___” meaning of first importance.

Answer 1

proteios

Question 2

Mix 1 ml of 1% egg albumin and 1 ml of 5 % NaOH in a test tube. Add 2-3 drops 1% CuSO4 solution drop by drop and mix thoroughly after each addition.

Answer 2

BIURET TEST

Question 3

In the Biuuret test, what did you observe?

Answer 3

It turned purple

Question 4

What chemical structure in the protein molecule is responsible for the positive result in the Biuret Test?.

Answer 4

at least 2 peptide bonds

Question 5

Boil in a water bath, 1 ml of albumin solution, add 10 drops of Ninhydrin reagent..
Observation:

Answer 5

NINHYDRIN TEST:

Question 6

What did you observe with the ninhydrin test and what would make it positive?

Answer 6

it turns purple in color. This
signifies that the test is positive for alpha-amino acid or carboxylic acid.

Question 7

To 2 ml of albumin solution, add 1 mL of concentrated nitric acid. Boil the solution for about 1 minute. Cool the solution and add excess of concentrated ammonium hydroxide.

Answer 7

XANTHOPROTEIC TEST

Question 8

What did you observe with the xanthoproteic test and what would make it positive?

Answer 8

the solution turns a dark yellowish-brown color. It confirms the presence of aromatic groups (such as benzene, naphthalene, and anthracene).

Question 9

Boil in a water bath, 1 ml of albumin solution with 1mL of Millon’s reagent. Boil the solution gently for 30 seconds. Add 2 drops of 1%
sodium nitrite.

Answer 9

MILLON’S TEST

Question 10

What did you observe with the Millon’s test and what would make it positive?

Answer 10

a reddish brown color. This indicates the presence of tyrosine residue

Question 11

To 3 ml of albumin solution, add 2 drops of sodium hydroxide. Then add 4 drops of alpha naphtol. Next, add 10 drops bromine water.

Answer 11

SAKAGUCHI TEST

Question 12

What did you observe with the Sakaguchi test and what would make it positive?

Answer 12

pinkish red. This indicates the presence of an arginine or
guanidinium compound.

Question 13

To 1 mL albumin solution, add 1 ml of 40%NaOH and heat for a few minutes or more. Cool the tube in running water and add 2-3 drops of lead(II) acetate solution.

Answer 13

SULFUR TEST

Question 14

What did you observe with the Sulfur test and what would make it positive?

Answer 14

a brownish-black color. This means that The test is
positive for sulfur.

Question 15

Take 0.5mL sulphanilic acid, add 0.5 mL of 0.5% sodium nitrite and add 1 mL of protein solution. After waiting for 1 minute, add 10% sodium carbonate solution.

Answer 15

PAULY’S TEST

Question 16

What did you observe with the Pauly’s test and what would make it positive?

Answer 16

a deep crimson, almost like blood. This means a positive result since
it detects tyrosine and histidine.

Question 17

To 1 mL of protein solution, add a drop of formaldehyde then add a drop of mercuric sulfate. Hold the test tube slanted, add 1 mL of concentrated sulfuric acid.

Answer 17

Aldehyde Test

Question 18

What did you observe with the Aldehyde test and what would make it positive?

Answer 18

a purple and clear layer in this solution. This distinguishes aldehydes from ketones.

Question 19

1% copper sulfate

Answer 19

We observe that the solution turns light blue.

Question 20

1% silver nitrate

Answer 20

We observe the solution turns into a milky white color.

Question 21

1 % lead acetate

Answer 21

This solution also turns into a milky white color.

Question 22

5% tannic acid

Answer 22

The solution turns into a light reddish-brown color.

Question 23

Saturated picric acid

Answer 23

The solution turns bright orange-yellow.

Question 24

What test you use if you want to know if a substance contains proteins?

Answer 24

Biuret
Ninhydrin
Xanthoproteic
Millon
Sakaguchi
Sulfur
Aldehyde

Question 25

Differentiate a complete protein from an incomplete protein and give examples.

Answer 25

Complete proteins are those that have all nine essential amino acids that our bodies
cannot naturally make, whereas incomplete protein sources may have a few of the
nine, but not all of them.

Examples of complete proteins include animal proteins such as meat, poultry, fish,
eggs, and dairy.

Nuts and seeds.
‌Whole grains (like brown rice or whole-wheat bread)
‌Vegetables.
‌Legumes in the form of lentils, peas, and beans