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Proteins
 Are the most diverse biomolecules. They
make up muscles, skin, hair, enzymes,
hormones, hemoglobin, and antibodies.
 The basic structure unit of protein is amino
acid
Amino group
Side Chain
Carboxylic
Acid group
 In the solid state amino acids exist in the
dipolar form
The side chains are what differentiate amino
acids.
The side chains can be divided into four
categories:
1. Non polar
2. Polar Neutral
3. Polar Basic
4. Polar Acidic
Non polar
Polar Neutral
Polar Basic
Polar Acidic
Protein Formation
Amino acids are joined together to form
protein when the carboxylic end of one amino
acid reacts with the amino end of another
amino acid to form a protein.
This link between the two amino acids is
called Peptide Bond.
Protein Structure
Described in terms of four levels of
organization:
1. Primary Structure
2. Secondary Structure
3. Tertiary Structure
4. Quaternary Structure
Primary Structure
 A sequence chain of amino acids (Insuline)
Secondary Structure
Occurs when the sequence of amino acids are
linked by hydrogen bonds (hair, wool)
Hydrogen bond between
every N-H group and the
oxygen of C=O group in the
next turn of the helix
Hydrogen bond between
The amides group of linear
polypeptide
Tertiary Structure
The folding of α-helix and the β-plated sheet
of the secondary structure
Maintained by Hydrogen bonds,
Ionic bonds, Disulfide Linkages
And Dispersion forces between
side chains
Quaternary Structure
Two or more polypeptide subunits join
together to form the quaternary structure.
Classification of Proteins
Classification according to solubility:
1. Fibrous Proteins:
• In soluble in water
• Example:
Collagen (bones and teeth), Keratins (hair and
wool), Myosins (contractile muscles), Fibrin
(protein of blood clot)
Classification of Proteins
2. Globular proteins
• Soluble in water
• Examples:
Albumin (egg white and blood),
Globulins (antibodies, enzymes)
Classification of Proteins
Function in the body
1. Building of new cells
2. Valuable source of energy
3. Catalysis biochemical reactions (enzymes)
4. Transportation of Oxygen (hemoglobin)
5. Bodies defense against infection (antibodies)
6. Transmission of impulses (nerves)
Denaturation of Proteins
Occurs when there is a disruption of the
bonds that stabilize the secondary, tertiary or
quaternary structures of proteins.
When this occurs, the protein unfolds and is
no longer biologically active.
Denaturation is occurred by:
1. heat
2. acids and bases
3. organic compounds 4. heavy metal ions
Physical Properties
1. Solubility
2. Power of hydrogen ion
• pH near 7 because there is COOH (acid) and
NH3 (base)
• Proteins are amphoteric compounds, can
react with acids and bases.
Chemical Properties
1. Buret test
• General test for proteins.
2. Xanthoprotic test
Identify proteins with aromatic ring
+ve result  yellow add NaOHorange
3. Millon’s test
To distinguish the presence of phenolic hydroxyl
group
+ve test white ppt heat
brick red
4. Ppt of proteins with alcohols
5. ppt of proteins with acids