Protein Qualitative Tests

Question 1

Test for amines α-amino acids or free amino acids.

A. Ninhydrin test
B. Xanthoproteic test
C. Sakaguchi test
D. Fohl’s test
E. Pauly test

Answer 1

A. Ninhydrin test

Question 2

When exposed to ninhydrin, the amino acid undergoes oxidative deamination that releases?

Answer 2

CO2 and an aldehyde

Question 3

What does amino-containing ninhydrin then form a complex with another ninhydrin molecule to form?

Answer 3

Diketohydrin

Question 4

Diketohydrin otherwise called?

Answer 4

Ruhemann’s complex

Question 5

Which test is responsible for the dark purple color?

A. Ninhydrin test
B. Xanthoproteic test
C. Sakaguchi test
D. Fohl’s test
E. Pauly test

Answer 5

A. Ninhydrin test

Question 6

Test for peptide bonds, a minimum of two peptide bonds/3 AAs.

A. Biuret Test
B. Millon’s Test
C. Hopkins-Cole Test
D. Reduces Sulfur Test

Answer 6

A. Biuret Test

Question 7

Consider the following:

Statement 1: In the biuret test, all proteins should be positive
Statement 2: While free amino acids yield negative
Statement 3: The greater the peptide bonds, the greater the color intensity

A. One statement is correct
B. Two statements are correct
C. Three statements are correct
D. None of the statements are correct

Answer 7

C. Three statements are correct

Question 8

In the Biuret test, what ion forms a violet-colored chelate complex with peptide bonds in alkaline
conditions?

A. NH4+
B. PO43-
C. Cu2+
D. HCO3-

Answer 8

C. Cu2+

Question 9

This test is specific for sulfur-containing amino acids cysteine, cystine, and methionine.

A. Biuret Test
B. Millon’s Test
C. Hopkins-Cole Test
D. Reduces Sulfur Test

Answer 9

D. Reduces Sulfur Test

Question 10

Which test is responsible for oxidizing to black-colored lead sulfides?

A. Biuret Test
B. Millon’s Test
C. Hopkins-Cole Test
D. Reduces Sulfur Test

Answer 10

D. Reduces Sulfur Test

Question 11

• This test is for phenol groups/derivatives, tyrosine.
• Not specific to proteins and will test positive for other phenol derivatives.

A. Biuret Test
B. Millon’s Test
C. Hopkins-Cole Test
D. Reduces Sulfur Test

Answer 11

B. Millon’s Test

Question 12

In Millon’s test, what radical form that responsible for the color of a red-colored complex with mercury?

A. Hydroxybenzene
B. Phenylalanine
C. Triol
D. Acetic acid

Answer 12

A. Hydroxybenzene

Question 13

Consider the following:

Statement 1: Initially, the phenol group of tyrosine is nitrated.
Statement 2: The only amino acid with a hydroxybenzene (phenol) group is tyrosine.
Statement 3: Upon the application of heat, the nitrated tyrosine forms a complex with mercury.

A. One statement is correct
B. Two statements are correct
C. Three statements are correct
D. None of the statements are correct

Answer 13

C. Three statements are correct

Question 14

This test is for aromatic amino acids, tyrosine, and tryptophan.

A. Ninhydrin test
B. Xanthoproteic test
C. Sakaguchi test
D. Fohl’s test
E. Pauly test

Answer 14

B. Xanthoproteic test

Question 15

In the Xanthoproteic test, what amino acids yield a negative result due to the stability of its side chain?

A. Hydroxybenzene
B. Phenylalanine
C. Triol
D. Acetic acid

Answer 15

B. Phenylalanine

Question 16

In the Xanthoproteic test, what color results do aromatic compounds react with HNO3 in a nitration reaction?

A. Red
B. Orange-yellow
C. Yellow
D. Black

Answer 16

C. Yellow

Question 17

In the Xanthroproteic test, what color upon the addition of a base, the color further intensifies and turns almost?

A. Red
B. Orange-yellow
C. Yellow
D. Black

Answer 17

B. Orange-yellow

Question 18

This test is for indole groups, tryptophan, or ‘glyoxylic acid reaction.’

A. Biuret Test
B. Millon’s Test
C. Hopkins-Cole Test
D. Reduces Sulfur Test

Answer 18

C. Hopkins-Cole Test

Question 19

In the Hopkins-Cole test, in the presence of indole-containing compounds like tryptophan, glyoxylic acid undergoes a condensation reaction, forming what color?

A. Purple
B. Pink
C. Blue
D. Orange

Answer 19

A. Purple

Question 20

In the Hopkin-Cole test, among which would be tryptophan, hence the formation of a purple color at the interface?

A. H2SO4
B. HCO3-
C. NH3
D. HBrO3

Answer 20

A. H2SO4

Question 21

In the Sakaguchi test, under alkaline conditions, the guanidine group of arginine can react with naphthol and NaOBr, forming what color?

A. Purple
B. Pink
C. Red
D. Orange

Answer 21

C. Red

Question 21

This test is for guanidine and arginine.

A. Ninhydrin test
B. Xanthoproteic test
C. Sakaguchi test
D. Fohl’s test
E. Pauly test

Answer 21

C. Sakaguchi test

Question 22

This test is for sulfur, cysteine, and cystine.

A. Ninhydrin test
B. Xanthoproteic test
C. Sakaguchi test
D. Fohl’s test
E. Pauly test

Answer 22

D. Fohl’s test

Question 23

In Fohl’s test, what amino acids do not yield a positive result due to the inert nature of their sulfur
atom.

A. Phenylalanine
B. Methionine
C. Theoronine
D. Tyrosine

Answer 23

B. Methionine

Question 24

In Fohl's test, when heated in alkaline conditions, the sulfur in sulfur-containing amino acids reacts with lead, resulting in a black precipitate in the form of? A. Sulfuric acid B. Ammonium chloride C. Lead sulfide D. Sodium bicarbonate

Answer 24

C. Lead sulfide

Question 25

This test is for imidazole, histidine, and phenol/hydroxy benzyl groups, and tyrosine. A. Ninhydrin test B. Xanthoproteic test C. Sakaguchi test D. Fohl's test E. Pauly test

Answer 25

E. Pauly test

Question 25

In the Pauly test, what reagent is first prepared through sulfanilic acid with NaNO2? A. Tollen's reagent B. Millon's reagent C. Collin's reagent D. Diazo's reagent

Answer 25

D. Diazo's reagent

Question 26

In the Pauly test, the Diazo reaction will likely form what color? A. Purple precipitate B. Pink-colored complex C. Red-colored complex D. Orange precipitate

Answer 26

C. Red-colored complex

Question 27

This protein precipitation is required 1% acetic acid A. Protein precipitation by heat B. Protein precipitation by heavy metal salts C. Protein precipitation by strong mineral acids D. Protein precipitation by alkaloidal reagents E. Protein precipitation by alcohol

Answer 27

A. Protein precipitation by heat

Question 28

This protein precipitation requires concentrated Nitric acid. A. Protein precipitation by heat B. Protein precipitation by heavy metal salts C. Protein precipitation by strong mineral acids D. Protein precipitation by alkaloidal reagents E. Protein precipitation by alcohol

Answer 28

C. Protein precipitation by strong mineral acids

Question 29

This protein precipitation requires lead acetate and ferric chloride. A. Protein precipitation by heat B. Protein precipitation by heavy metal salts C. Protein precipitation by strong mineral acids D. Protein precipitation by alkaloidal reagents E. Protein precipitation by alcohol

Answer 29

B. Protein precipitation by heavy metal salts

Question 30

This protein precipitation requires tannic acid and picric acid. A. Protein precipitation by heat B. Protein precipitation by heavy metal salts C. Protein precipitation by strong mineral acids D. Protein precipitation by alkaloidal reagents E. Protein precipitation by alcohol

Answer 30

D. Protein precipitation by alkaloidal reagents

Question 31

This protein precipitation requires absolute alcohol A. Protein precipitation by heat B. Protein precipitation by heavy metal salts C. Protein precipitation by strong mineral acids D. Protein precipitation by alkaloidal reagents E. Protein precipitation by alcohol

Answer 31

E. Protein precipitation by alcohol

Question 32

It is the main protein component of egg whites. It is a globular, water-soluble glycoprotein.

Answer 32

Ovalbumin

Question 33

In precipitation by heat, before acetic acid, the heat disrupts hydrogen bonding, leading to protein unfolding (denaturation) and exposing nonpolar amino acid residues, what would happen? A. It would increase protein solubility B. It would decrease protein solubility C. It would increase denatures protein solubility D. It would decrease denatures protein solubility

Answer 33

B. It would decrease protein solubility

Question 34

In precipitation by heat, before acetic acid, exposing nonpolar amino acid residues that cause decreased protein solubility would be the result EXCEPT: A. Proteins in egg whites B. Denatures protein C. Coagulated proteins D. Protein-water interaction favored

Answer 34

D. Protein-water interaction favored

Question 35

In precipitation by heat, after acetic acid, the addition of the acid shifts the pH of the system closer to the isoelectric point of ovalbumin (pI = 4.5). What would happen? A. Proteins are least soluble at their isoelectric point. B. Proteins are more insoluble at their isoelectric point. C. Proteins are least insoluble at their isoelectric points. D. Proteins are more soluble at their isoelectric point.

Answer 35

A. Proteins are least soluble at their isoelectric point.

Question 36

In heavy metal salts, Fe3+, Pb2+, and similar heavy metal cations interact with the negatively charged carboxylate (-COO-) groups and electron pairs of amino acid residues in ovalbumin to form. A. Anionic organic acids interact with positively charged groups of amino acid residues. B. It complexes that precipitate out the protein. C. It prevents proper protein folding. D. Abundance of protons disrupts the hydrogen bonds and salt bridges.

Answer 36

B. It complexes that precipitate out the protein.

Question 37

In strong mineral acids, what chemical abundance of protons disrupts the hydrogen bonds, ionic bonds, salt bridges, and disulfide bridges present, preventing proper protein folding? A. H2SO4 & PO43- B. HNO3 & H2SO4 C. NO2- & H3O+ D. Cr2O72- & ClO3-

Answer 37

B. HNO3 & H2SO4

Question 38

In alkaloidal reagents, what anionic organic acids interact with positively charged groups of amino acid residues, preventing proper folding? A. Aspartic acid & Acetic acid B. Chromic acid & Aspartic acid C. Tannic acid & Picric acid D. Chromium acid & Tannic acid

Answer 38

C. Tannic acid & Picric acid

Question 39

In organic solvents, this leads to organic solvents displacing the water molecules associated with the protein (dehydration), resulting in protein denaturation and precipitation.

Answer 39

Ethanol