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Proteins and Amino
 The amino acids are the building blocks of Proteins
 Proteins are the fundamental structural components
of the body
Contractile proteins in the muscles to permit movement
Collagen in the bones
Plasma albumin, hemoglobin in blood
Immunoglobin to destroy infectious bacterial and viruses
Storage proteins (ferrin that bind to iron and help in its
Maintain the osmotic pressure
 More than 300 different amino acids are known in
 Only 20 are commonly found as constituents of
mammalian proteins
Amino acids structure
• At physiologic PH= 7.6 the amino
exists as Zwitterion
• The carboxyl group dissociate to
form coo –
• The amino group is protonate to
form NH3+
Protein formation
N terminal
C terminal
Physical properties
 Colorless
 Crystalline
 More soluble in water than in polar solvents
 They have high melting points more than 200 C
Nutritional classification of amino acids
Essential amino acids:
Non-essential amino acids
 Cannot be synthesized
 Can be made by the
by the body
 Must be taken from the
 Ex: Valine, leucine,
phenylalanine, and
Classification according to amino acids side chain
Qualitative Tests for
Amino Acids
1- Ninhydrin Reaction:
 A color reaction given by amino acids and
peptides on heating with the chemical ninhydrin.
 The technique is widely used for the detection
and quantitation (measurement) of amino acids
and peptides.
 Ninhydrin is a powerful oxidizing agent which
reacts with all amino acids between pH 4-8 to
produce a purple colored-compound.
1- Ninhydrin Reaction
 The reaction is also given by primary amines and
ammonia but without the liberation of Co2
 The amino acids proline and hydroxyproline also
reacts but produce a yellow color.
 Alpha-amino acid + 2 ninhydrin ---> CO2 +
aldehyde + final complex (purple) + 3H2O
1- Ninhydrin Reaction
 Method:
1 ml AA + 1 ml NH---- heat in boiling WB for 5min----Purple color
2-Xanthoproteic Reaction:
 This reaction is specific for aromatic amino acids
 This reaction involves the nitration of benzene nucleus in
alkaline medium
2-Xanthoproteic Reaction:
 Aromatic AAs form yellow nitro derivative on
heating with conc. nitric acid, the salts of these
derivatives are orange.
Nitrated tyrosine (a) and tryptophan (b)
2-Xanthoproteic Reaction:
 Method:
1 ml AA + 1 ml conc. HNO3----- heat the mixture in
WB for 30s--cool--add drop-wise 40% NaOH to
render the solution alkaline--- Yellow to orange color.
3- Millon Reaction:
 This reaction is used to detect the presence of phenol
(hydroxybenzene) which reacts with Millon's reagent to
form red complexes.
 - The only phenolic AA is tyrosine.
3- Millon Reaction:
 Method:
1 ml AA + 5 drops of Millon reagent ----- heat the
mixture in BWB for 10min--cool too room temp-add 5 drops of NaNO2---Brick red color.
4- Hopkin-cole Reaction:
 This reaction is used to detect the presence of indol group
 The indol group of tryptophan reacts with glyoxalic acid in
the presence of conc. H2SO4 to give purple color.
4- Hopkin-cole Reaction:
 Method:
1 ml AA + 1 ml Hopkin-cole reagent -----mix well-Carefully pour conc. H2SO4 down the side of the
tube so as to form two layers --Purple ring at the
5- Sulfur Test:
 This reaction is specific to detect the presence of sulfur
 -The sulfur of cystein and cystine is converted to inorganic
sulfide with conc. NaOH. Lead acetate is added and a ppt of
black lead sulfide indicates a +ve reaction.
5- Sulfur Test:
 Method:
2 ml AA + 1 ml 40% NaOH + 1-3 drops of lead
acetate solution----- heat the mixture in WB
for 3min -----cool--observe any change ---- Black ppt.
6-Sakaguchi Reaction:
 This reaction is used to detect the presence of guanidine
 -The only AA that contains guanidine group is arginine
which reacts with α-naphthol and an oxidizing agent such
as bromide water to give a red color
6-Sakaguchi Reaction:
 Method:
2 ml AA + 1 ml 2M NaOH + 1 ml ethanolic 0.02% αnaphthol ----- mix wellcool in ice-----add 1 ml of
alkaline hypochlorite solution---- Red color