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Biochemistry LAB > COLOR REACTIONS OF PROTEINS AND AMINO ACIDS > Flashcards

COLOR REACTIONS OF PROTEINS AND AMINO ACIDS Flashcards

1
Q

1 ml = ???

A

20 drops

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2
Q

Few drops = ???

A

3 to 5 drops

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3
Q

Unspecified time for heating

A

5 mins

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4
Q

the building blocks of proteins

A

Amino acids

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5
Q

The general reactions of amino acids are mostly due to the
presence of two functional groups namely __________ and __________

A

carboxyl (-COOH) group and amino (-NH2) group

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6
Q

limitation of reaction tests

A

some non-protein substances can also give positive response to some of the
color tests

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7
Q
  • NH3
A

Amino group

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8
Q
  • COOH
A

Carboxylic acid group

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9
Q

it is where all four species are attached

A

(alpha) α - carbon

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10
Q

Side chain

A

R - group

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11
Q

simplest amino acid

A

aminoacetic acid → glycine

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12
Q

two amino acids

A

Dipeptide

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13
Q

three amino acids

A

Tripeptide

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14
Q

50 amino acids or more

A

Proteins or polypeptides

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15
Q

General Steps in Peptide Bond Formation

A
  1. Amino group on one amino acid molecule + carboxyl group on another amino acid
  2. Release of a molecule of water and formation of a peptide bond.
  3. The reactive amino group on the left and the reactive carboxyl group on the right can still react with additional amino acids to lengthen the peptide.
  4. The process can continue until thousands of units have joined, resulting in large proteins.
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16
Q

pH at which an amino acid exists as a Zwitterion

A

Isoelectric point

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17
Q

hydrogen is in excess

A

acid solution

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18
Q

OHion is in excess

A

alkaline solution

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19
Q

Product of internal transfer of a hydrogen ion from the -COOH group to the -NH2 group to leave an ion with both a negative charge and a positive charge.

A

zwitterion

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20
Q

isoelectric points: Acidic amino acids

A

aspartic acid (2.8), glutamic acid (3.2)

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21
Q

isoelectric points: Neutral amino acids

A

(5.0 to 6.3)

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22
Q

isoelectric points: Basic amino acids

A

lysine (9.7), arginine (10.8), histidine (7.6)

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23
Q

base + amino acid in zwitterion form

A

Amino acid as an acid

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24
Q

acid + amino acid in zwitterion

A

Amino acid as base

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25
Q

zwitterion form:

A

ionized form (-COO-) of carboxylic group - base

ionized form (-NH3+) of amino group - acid

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26
Q

(alpha) α - carbon other name

A

chiral

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27
Q

four different constituents/species and that the α - carbon is asymmetric.

A

chiral

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28
Q

α - carbon shape

A

asymmetric → two possible, non-superimposable, mirror images of the amino acids.

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29
Q

Clockwise rotation

A

“dextrorotatory”

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30
Q

Counter clockwise:

A

“levorotatory”

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31
Q

a pair of molecules that exist in two forms that are mirror images of one another but cannot be superimposed one upon the other.

A

Enantiomers

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32
Q

Enantiomeric molecules

A

optical property/optical activity → ability to rotate the plane of polarized light

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33
Q

All common amino acids are the _________

A

L-enantiomer

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34
Q

capacity to interact with water

A

Polarity

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35
Q

Classification of Amino Acids Based on Polarity

A

(1) nonpolar,
(2) polar-neutral,
(3) polar-acidic, and
(4) polar-basic.

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36
Q

hydrophobic (“water-fearing”); not attracted to water molecules

A

Nonpolar Amino Acids

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37
Q

Nonpolar Amino Acids

A
  1. Glycine
  2. Alanine
  3. Valine
  4. Leucine
  5. Isoleucine
  6. Proline
  7. Phenylalanine
  8. Methionine
  9. Tryptophan
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38
Q

In solution at physiological pH - side chain of this amino acid is neither acidic nor basic.

A

Polar neutral amino acids

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39
Q

More soluble in water than the nonpolar amino acids as, in each case, the R group present can form hydrogen bond to water

A

Polar neutral amino acids

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40
Q

Polar neutral amino acids

A
  1. Serine
  2. Cysteine
  3. Threonine
  4. Asparagine
  5. Glutamine
  6. Tyrosine
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41
Q

In solution at physiological pH - side chain of this amino acid bears a negative charge; the side-chain carboxyl group has lost its hydrogen atom.

A

Polar acidic amino acid

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42
Q

Polar acidic amino acid

A
  1. Aspartic acid
  2. Glutamic Acid
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43
Q

In solution at physiological pH - side chain of this amino acid bears a positive charge; the nitrogen atom of the amino group has accepted a proton.

A

Polar basic amino acid

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44
Q

Polar basic amino acid

A
  1. Histidine
  2. Lysine
  3. Arginine
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45
Q

side chain is H or alkyl (nonpolar)

A
  1. Glycine
  2. Alanine
  3. Valine
  4. Leucine
  5. Isoleucine
  6. Phenylalanine
  7. Proline
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46
Q

side chain contains an -OH group (hydroxyl)

A
  1. Serine
  2. Threonine
  3. Tyrosine
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47
Q

side chain contains sulfur

A
  1. Cysteine
  2. Methionine
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48
Q

side chain contains nonbasic nitrogen

A
  1. Asparagine
  2. Glutamine
  3. Tryptophan
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49
Q

Side chain is acidic

A
  1. Aspartic acid
  2. Glutamic acid
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50
Q

side chain is basic

A
  1. Lysine
  2. Arginine
  3. Histidine
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51
Q

properties and reactions due to

A

Basic amino group and an acidic carboxyl group
Side chains
Dipolar nature/zwitterion form

52
Q

Solubility

A

generally soluble in water and insoluble in non-polar organic solvents; -> polar water molecules and the zwitterions

53
Q

Decomposition and melting tend _________ range

A

200 - 300°C

54
Q

__________ solids with __________ melting points;

A

crystalline; high

55
Q

Usual taste of amino acid

A

sour or umami

56
Q

tasteless

57
Q

Sweet

A
  1. Glycine
  2. Alanine
  3. Valine
58
Q

Bitter

A
  1. Arginine
  2. Isoleucine
59
Q

Chemical Reactions

A
  1. Reaction due to the carboxylic group (-COOH)
  2. Reaction due to the amino group (-NH2)
60
Q

Reaction due to the carboxylic group (-COOH)

A

A. Salt formation: Amino + amino
B. Salt formation: Base
C. Ester Formation - Alcohol
D. Decarboxylation
E. Reaction to ammonia

61
Q
  1. Reaction due to the amino group (-NH2)
A

A. Salt formation - Acid
B. Reaction with Ninhydrin
C. Transamination
D. Oxidative deamination

62
Q

zwitterion in low pH

63
Q

zwitterion in high pH

64
Q

they can act either as a base or an acid

A

amphoteric

65
Q

Formation of peptide is a _________ process

A

Condensation

66
Q

Optical Activity is determined by

A

Polarimeter

67
Q

L-amino acid taste

A

sweet or bitter taste

68
Q

D-amino acid

69
Q

Salt is formed by

A

acid-base neutralization reaction

70
Q

Salt formation

A

amino groups behave as bases and combine with acids

Amino acids form salts (COONa) with base

Amino acids can form esters (COOR) with alcohols

71
Q

removes a carboxyl group and releases carbon dioxide (CO2)

A

Decarboxylation

72
Q

could be used to develop latent fingerprints

73
Q

α-amino acids react with ninhydrin to form a

A

purple, blue or pink color complex (Ruhemann’s purple)

proline and hydroxyproline = yellow color

74
Q

Decarboxylation

A

Amino acid - (enzymes) -> amine

75
Q

Carboxyl group of dicarboxylic amino acid reacts with NH3 to form an amide

A

Reaction with ammonia

76
Q

Reduce ninhydrin

A

hydrindantin

77
Q

transfer of an amino group from an amino acid to a keto acid to form a new amino acid

A

Transamination

78
Q

Transamination is catalyzed by the family of enzymes called

A

transaminase

79
Q

transaminases require the participation of aldehyde-containing enzyme called

A

pyridoxal phosphate (PLP)

80
Q

amino acid is converted into the corresponding keto acid by the removal of the amine functional group (NH2)

provide NH3 + for urea synthesis and a-keto acids for a variety of reactions

occurs primarily on glutamic acid

A

Oxidative deamination

80
Q

amino acid is converted into the corresponding keto acid by the removal of the amine functional group (NH2)

provide NH3 + for urea synthesis and a-keto acids for a variety of reactions

occurs primarily on glutamic acid

A

Oxidative deamination

80
Q

amino acid is converted into the corresponding keto acid by the removal of the amine functional group (NH2)

provide NH3 + for urea synthesis and a-keto acids for a variety of reactions

occurs primarily on glutamic acid

A

Oxidative deamination

81
Q

amino acid is converted into the corresponding keto acid by the removal of the amine functional group (NH2)

provide NH3 + for urea synthesis and a-keto acids for a variety of reactions

occurs primarily on glutamic acid

A

Oxidative deamination

82
Q

BIURET TEST positive result

A

Color produced may vary from pink to blue

83
Q

BIURET TEST Reactive group:

A

Proteins and peptides with at least two peptide linkages give positive
biuret test;

histidine

84
Q

BIURET TEST Principle:

A

alkaline copper (II) sulphate + peptides/proteins (–CONH2) → violet complex

85
Q

NINHYDRIN TEST Positive Result:

A

Intense blue or purple compound

(proline and hydroxyproline) = yellow color

86
Q

NINHYDRIN TEST Reactive group

A

α-amino group; peptides

87
Q

NINHYDRIN TEST Principle:

A

▪ Oxidative deamination and decarboxylation.

Triketohydrindenehydrate + alpha-a.a./peptides → intense blue color or purple color

Imino acids (proline and hydroxyproline) + ninhydrin → yellow color

88
Q

XANTHOPROTEIC TEST Positive Result:

A

orange colored derivative salts

89
Q

XANTHOPROTEIC TEST Reactive group:

A

aromatic ring of tyrosine and tryptophan

90
Q

XANTHOPROTEIC TEST Principle:

A

tyrosine/tryptophan + HNO3→ nitration of the phenyl group → yellow derivatives + alkali→ orange colored derivative salts

91
Q

MILLON’S TEST Positive Result:

A

old rose-colored complex

92
Q

MILLON’S TEST Reactive group:

A

phenolic ring of tyrosine

93
Q

MILLON’S TEST Principle:

A

Tyrosine + NaNO2 → nitration of hydroxyphenyl group of
tyrosine + mercuric sulfate → old rose colored salt

94
Q

MILLON’S TEST Interfering compounds:

A

alkalis and chlorides

95
Q

MILLON’S TEST Remedy:

A

addition of sodium nitrite or extra mercuric sulphate

96
Q

HOPKINS-COLE REACTION Positive Result:

A

violet complex

97
Q

HOPKINS-COLE REACTION Reactive group:

A

indole ring of tryptophan

98
Q

HOPKINS-COLE REACTION Principle:

A

▪ a.a. (indole group) + glyoxylic acid (aldehyde group) →
VIOLET/PURPLE COMPLEX

99
Q

HOPKINS-COLE REACTION Interfering compounds:

A

nitrites, nitrates, chlorides and chlorates

100
Q

HOPKINS-COLE REACTION Remedy:

A

pure sulfuric acid

101
Q

BROMINE WATER TEST Positive Result:

A

pinkish lavender complex

102
Q

BROMINE WATER TEST Reactive group:

A

indole ring of tryptophan

103
Q

BROMINE WATER TEST Principle:

A

▪ Bromine water + Tryptophan + n-amyl alcohol → PINKISH LAVENDER COMPLEX (soluble at alcohol layer)

104
Q

BROMINE WATER TEST Note:

A

color of excess reagent→ masked pinkish lavender color

Remedy: accuracy in amounts of reagents

105
Q

PAULY REACTION Positive Result:

A

highly colored dyes

106
Q

PAULY REACTION Reactive group:

A

phenolic ring in tyrosine; imidazole ring in histidine

107
Q

PAULY REACTION Principle:

A

(diazotization)

108
Q

LEAD ACETATE REACTION Positive Result:

A

black precipitate

109
Q

LEAD ACETATE REACTION Reactive group:

A

Sulfhydril (-SH) group of cysteine, disulfide bond in cystine

110
Q

LEAD ACETATE REACTION Note:

A

methionine has sulphide (-S), not sulfhydryl group (-SH), thus it will yield a negative result

111
Q

NITROPRUSSIDE REACTION Positive Result:

A

▪ Red compound indicates free sulfhydryl group
▪ Purple compound indicates disulfide bonds

112
Q

NITROPRUSSIDE REACTION Reactive group:

A

▪ sulfhydril (-SH) group in cysteine
▪ disulfide bond in cystine

113
Q

SAKAGUCHI REACTION Positive Result:

A

red or orange color

114
Q

SAKAGUCHI REACTION Reactive group:

A

guanidino group of arginine

115
Q

SAKAGUCHI REACTION Principle:

A

Arginine + a-naphthol and sodium hypobromite →
red or orange colored complex

116
Q

SCHIFF’S TEST Positive Result:

A

magenta/pink color

117
Q

SCHIFF’S TEST Reactive group:

A

compounds containing aldehyde group; amino group of lysine

118
Q

SCHIFF’S TEST

A

Qualitative test for aldehydes

1st lysine + aldehyde → Schiff base
2nd Schiff base + Schiff reagent → Schiff Adduct (red or orange compound)

119
Q

FOLIN’S MCCARTHY SULLIVAN TEST Positive Result:

A

Red colour

120
Q

FOLIN’S MCCARTHY SULLIVAN TEST Reactive group:

A

Methionine

121
Q

FOLIN’S MCCARTHY SULLIVAN TEST Principle:

A

▪ Methionine + Sodium nitroprusside + HCl → red color

122
Q

ISATIN TEST Positive Result:

A

blue colored product

123
Q

ISATIN TEST Reactive group:

A

imino group of proline/hydroxyproline

124
Q

ISATIN TEST Principle:

A

Proline and hydroxyproline + isatin reagent → blue-colored
product.

Biochemistry LAB (5 decks)

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