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Biochemistry > Protein Qualitative Tests > Flashcards

Protein Qualitative Tests Flashcards

1
Q

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

A

A. Ninhydrin test

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2
Q

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

A

CO2 and an aldehyde

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3
Q

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

A

Diketohydrin

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4
Q

Diketohydrin otherwise called?

A

Ruhemann’s complex

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5
Q

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

A

A. Ninhydrin test

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6
Q

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

A

A. Biuret Test

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7
Q

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

A

C. Three statements are correct

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8
Q

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-

A

C. Cu2+

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9
Q

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

A

D. Reduces Sulfur Test

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10
Q

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

A

D. Reduces Sulfur Test

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11
Q
  • 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

A

B. Millon’s Test

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12
Q

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

A

A. Hydroxybenzene

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13
Q

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

A

C. Three statements are correct

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14
Q

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

A

B. Xanthoproteic test

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15
Q

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

A

B. Phenylalanine

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16
Q

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

A

C. Yellow

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17
Q

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

A

B. Orange-yellow

18
Q

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

A

C. Hopkins-Cole Test

19
Q

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

A

A. Purple

20
Q

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

A

A. H2SO4

21
Q

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

A

C. Red

21
Q

This test is for guanidine and arginine.

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

A

C. Sakaguchi test

22
Q

This test is for sulfur, cysteine, and cystine.

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

A

D. Fohl’s test

23
Q

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

A

B. Methionine

24
Q

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

A

C. Lead sulfide

25
Q

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

A

E. Pauly test

25
Q

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

A

D. Diazo’s reagent

26
Q

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

A

C. Red-colored complex

27
Q

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

A

A. Protein precipitation by heat

28
Q

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

A

C. Protein precipitation by strong mineral acids

29
Q

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

A

B. Protein precipitation by heavy metal salts

30
Q

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

A

D. Protein precipitation by alkaloidal reagents

31
Q

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

A

E. Protein precipitation by alcohol

32
Q

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

A

Ovalbumin

33
Q

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

A

B. It would decrease protein solubility

34
Q

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

A

D. Protein-water interaction favored

35
Q

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.

A

A. Proteins are least soluble at their isoelectric point.

36
Q

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.

A

B. It complexes that precipitate out the protein.

37
Q

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-

A

B. HNO3 & H2SO4

38
Q

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

A

C. Tannic acid & Picric acid

39
Q

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

A

Ethanol

Biochemistry (17 decks)

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