COLOR REACTIONS OF PROTEINS AND AMINO ACIDS Flashcards
(126 cards)
1
Q
1 ml = ???
A
20 drops
2
Q
Few drops = ???
A
3 to 5 drops
3
Q
Unspecified time for heating
A
5 mins
4
Q
the building blocks of proteins
A
Amino acids
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
6
Q
limitation of reaction tests
A
some non-protein substances can also give positive response to some of the
color tests
7
Q
- NH3
A
Amino group
8
Q
- COOH
A
Carboxylic acid group
9
Q
it is where all four species are attached
A
(alpha) α - carbon
10
Q
Side chain
A
R - group
11
Q
simplest amino acid
A
aminoacetic acid → glycine
12
Q
two amino acids
A
Dipeptide
13
Q
three amino acids
A
Tripeptide
14
Q
50 amino acids or more
A
Proteins or polypeptides
15
Q
General Steps in Peptide Bond Formation
A
- Amino group on one amino acid molecule + carboxyl group on another amino acid
- Release of a molecule of water and formation of a peptide bond.
- 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.
- The process can continue until thousands of units have joined, resulting in large proteins.
16
Q
pH at which an amino acid exists as a Zwitterion
A
Isoelectric point
17
Q
hydrogen is in excess
A
acid solution
18
Q
OHion is in excess
A
alkaline solution
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
20
Q
isoelectric points: Acidic amino acids
A
aspartic acid (2.8), glutamic acid (3.2)
21
Q
isoelectric points: Neutral amino acids
A
(5.0 to 6.3)
22
Q
isoelectric points: Basic amino acids
A
lysine (9.7), arginine (10.8), histidine (7.6)
23
Q
base + amino acid in zwitterion form
A
Amino acid as an acid
24
Q
acid + amino acid in zwitterion
A
Amino acid as base
25
zwitterion form:
ionized form (-COO-) of carboxylic group - base
ionized form (-NH3+) of amino group - acid
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(alpha) α - carbon other name
chiral
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four different constituents/species and that the α - carbon is asymmetric.
chiral
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α - carbon shape
asymmetric → two possible, non-superimposable, mirror images of the amino acids.
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Clockwise rotation
"dextrorotatory"
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Counter clockwise:
"levorotatory”
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a pair of molecules that exist in two forms that are mirror images of one another but cannot be superimposed one upon the other.
Enantiomers
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Enantiomeric molecules
optical property/optical activity → ability to rotate the plane of polarized light
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All common amino acids are the _________
L-enantiomer
34
capacity to interact with water
Polarity
35
Classification of Amino Acids Based on Polarity
(1) nonpolar,
(2) polar-neutral,
(3) polar-acidic, and
(4) polar-basic.
36
hydrophobic (“water-fearing”); not attracted to water molecules
Nonpolar Amino Acids
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Nonpolar Amino Acids
1. Glycine
2. Alanine
3. Valine
4. Leucine
5. Isoleucine
6. Proline
7. Phenylalanine
8. Methionine
9. Tryptophan
38
In solution at physiological pH - side chain of this amino acid is neither acidic nor basic.
Polar neutral amino acids
39
More soluble in water than the nonpolar amino acids as, in each case, the R group present can form hydrogen bond to water
Polar neutral amino acids
40
Polar neutral amino acids
1. Serine
2. Cysteine
3. Threonine
4. Asparagine
5. Glutamine
6. Tyrosine
41
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.
Polar acidic amino acid
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Polar acidic amino acid
1. Aspartic acid
2. Glutamic Acid
43
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.
Polar basic amino acid
44
Polar basic amino acid
1. Histidine
2. Lysine
3. Arginine
45
side chain is H or alkyl (nonpolar)
1. Glycine
2. Alanine
3. Valine
4. Leucine
5. Isoleucine
6. Phenylalanine
7. Proline
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side chain contains an -OH group (hydroxyl)
1. Serine
2. Threonine
3. Tyrosine
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side chain contains sulfur
1. Cysteine
2. Methionine
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side chain contains nonbasic nitrogen
1. Asparagine
2. Glutamine
3. Tryptophan
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Side chain is acidic
1. Aspartic acid
2. Glutamic acid
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side chain is basic
1. Lysine
2. Arginine
3. Histidine
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properties and reactions due to
Basic amino group and an acidic carboxyl group
Side chains
Dipolar nature/zwitterion form
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Solubility
generally soluble in water and insoluble in non-polar organic solvents; -> polar water molecules and the zwitterions
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Decomposition and melting tend _________ range
200 - 300°C
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__________ solids with __________ melting points;
crystalline; high
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Usual taste of amino acid
sour or umami
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tasteless
Leucine
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Sweet
1. Glycine
2. Alanine
3. Valine
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Bitter
1. Arginine
2. Isoleucine
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Chemical Reactions
1. Reaction due to the carboxylic group (-COOH)
2. Reaction due to the amino group (-NH2)
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Reaction due to the carboxylic group (-COOH)
A. Salt formation: Amino + amino
B. Salt formation: Base
C. Ester Formation - Alcohol
D. Decarboxylation
E. Reaction to ammonia
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2. Reaction due to the amino group (-NH2)
A. Salt formation - Acid
B. Reaction with Ninhydrin
C. Transamination
D. Oxidative deamination
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zwitterion in low pH
cation
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zwitterion in high pH
anion
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they can act either as a base or an acid
amphoteric
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Formation of peptide is a _________ process
Condensation
66
Optical Activity is determined by
Polarimeter
67
L-amino acid taste
sweet or bitter taste
68
D-amino acid
Sweet
69
Salt is formed by
acid-base neutralization reaction
70
Salt formation
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
removes a carboxyl group and releases carbon dioxide (CO2)
Decarboxylation
72
could be used to develop latent fingerprints
ninhydrin
73
α-amino acids react with ninhydrin to form a
purple, blue or pink color complex (Ruhemann’s purple)
proline and hydroxyproline = yellow color
74
Decarboxylation
Amino acid - (enzymes) -> amine
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Carboxyl group of dicarboxylic amino acid reacts with NH3 to form an amide
Reaction with ammonia
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Reduce ninhydrin
hydrindantin
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transfer of an amino group from an amino acid to a keto acid to form a new amino acid
Transamination
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Transamination is catalyzed by the family of enzymes called
transaminase
79
transaminases require the participation of aldehyde-containing enzyme called
pyridoxal phosphate (PLP)
80
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
Oxidative deamination
80
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
Oxidative deamination
80
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
Oxidative deamination
81
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
Oxidative deamination
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BIURET TEST positive result
Color produced may vary from pink to blue
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BIURET TEST Reactive group:
Proteins and peptides with at least two peptide linkages give positive
biuret test;
histidine
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BIURET TEST Principle:
alkaline copper (II) sulphate + peptides/proteins (–CONH2) → violet complex
85
NINHYDRIN TEST Positive Result:
Intense blue or purple compound
(proline and hydroxyproline) = yellow color
86
NINHYDRIN TEST Reactive group
α-amino group; peptides
87
NINHYDRIN TEST Principle:
▪ Oxidative deamination and decarboxylation.
Triketohydrindenehydrate + alpha-a.a./peptides → intense blue color or purple color
Imino acids (proline and hydroxyproline) + ninhydrin → yellow color
88
XANTHOPROTEIC TEST Positive Result:
orange colored derivative salts
89
XANTHOPROTEIC TEST Reactive group:
aromatic ring of tyrosine and tryptophan
90
XANTHOPROTEIC TEST Principle:
tyrosine/tryptophan + HNO3→ nitration of the phenyl group → yellow derivatives + alkali→ orange colored derivative salts
91
MILLON’S TEST Positive Result:
old rose-colored complex
92
MILLON’S TEST Reactive group:
phenolic ring of tyrosine
93
MILLON’S TEST Principle:
Tyrosine + NaNO2 → nitration of hydroxyphenyl group of
tyrosine + mercuric sulfate → old rose colored salt
94
MILLON’S TEST Interfering compounds:
alkalis and chlorides
95
MILLON’S TEST Remedy:
addition of sodium nitrite or extra mercuric sulphate
96
HOPKINS-COLE REACTION Positive Result:
violet complex
97
HOPKINS-COLE REACTION Reactive group:
indole ring of tryptophan
98
HOPKINS-COLE REACTION Principle:
▪ a.a. (indole group) + glyoxylic acid (aldehyde group) →
VIOLET/PURPLE COMPLEX
99
HOPKINS-COLE REACTION Interfering compounds:
nitrites, nitrates, chlorides and chlorates
100
HOPKINS-COLE REACTION Remedy:
pure sulfuric acid
101
BROMINE WATER TEST Positive Result:
pinkish lavender complex
102
BROMINE WATER TEST Reactive group:
indole ring of tryptophan
103
BROMINE WATER TEST Principle:
▪ Bromine water + Tryptophan + n-amyl alcohol → PINKISH LAVENDER COMPLEX (soluble at alcohol layer)
104
BROMINE WATER TEST Note:
color of excess reagent→ masked pinkish lavender color
Remedy: accuracy in amounts of reagents
105
PAULY REACTION Positive Result:
highly colored dyes
106
PAULY REACTION Reactive group:
phenolic ring in tyrosine; imidazole ring in histidine
107
PAULY REACTION Principle:
(diazotization)
108
LEAD ACETATE REACTION Positive Result:
black precipitate
109
LEAD ACETATE REACTION Reactive group:
Sulfhydril (-SH) group of cysteine, disulfide bond in cystine
110
LEAD ACETATE REACTION Note:
methionine has sulphide (-S), not sulfhydryl group (-SH), thus it will yield a negative result
111
NITROPRUSSIDE REACTION Positive Result:
▪ Red compound indicates free sulfhydryl group
▪ Purple compound indicates disulfide bonds
112
NITROPRUSSIDE REACTION Reactive group:
▪ sulfhydril (-SH) group in cysteine
▪ disulfide bond in cystine
113
SAKAGUCHI REACTION Positive Result:
red or orange color
114
SAKAGUCHI REACTION Reactive group:
guanidino group of arginine
115
SAKAGUCHI REACTION Principle:
Arginine + a-naphthol and sodium hypobromite →
red or orange colored complex
116
SCHIFF’S TEST Positive Result:
magenta/pink color
117
SCHIFF’S TEST Reactive group:
compounds containing aldehyde group; amino group of lysine
118
SCHIFF’S TEST
Qualitative test for aldehydes
1st lysine + aldehyde → Schiff base
2nd Schiff base + Schiff reagent → Schiff Adduct (red or orange compound)
119
FOLIN'S MCCARTHY SULLIVAN TEST Positive Result:
Red colour
120
FOLIN'S MCCARTHY SULLIVAN TEST Reactive group:
Methionine
121
FOLIN'S MCCARTHY SULLIVAN TEST Principle:
▪ Methionine + Sodium nitroprusside + HCl → red color
122
ISATIN TEST Positive Result:
blue colored product
123
ISATIN TEST Reactive group:
imino group of proline/hydroxyproline
124
ISATIN TEST Principle:
Proline and hydroxyproline + isatin reagent → blue-colored
product.
