Page 14 - Lesson Notes - Biomolecules 1

Types of Proteins
Proteins are classified on the basis of shape, chemical composition and function.
Accordingly on the basis of shape these are of two main types
i. Fibrous Proteins
The proteins have spiral secondary polypeptide chains wound around each other in
order to form fibres. These are insoluble in water generally, but soluble in
concentrated acids, alkalis and salts, e.g., Collagen of connective tissue, keratin of
hair, etc.
ii. Globular Proteins
They are rounded in shape and are generally soluble in water and in dilute acids,
alkalis, salts, e.g., Egg albumin, serum globulins.
Note:
Collagen, the most abundant protein of animal world and Ribulose Bisphosphate
Carboxylase Oxygenase (RuBisCO) is the most abundant protein in plants and the
whole of the biosphere.
Functions of Proteins
Proteins have various basic functions in living organism given below . Helps in
transportation of nutrients across the cell membrane by acting as protein
transporter.
(ii) Helps in fighting with infectious organism.
(iii) These are helpful in movement of muscles, e.g., Myosin and actin.
(iv) Helps in maintenance of pH and regulation of the volume of body fluids.
(v) Helps at the time of injury in blood clotting and acts as antibodies and provide
immunity.
(vi) Helps in growth and repair of body tissues.
(vii) Some proteins function as hormones and some functin as enzymes and
catalyse the reactions.
Denaturation of Proteins
When proteins are exposed to extreme change in pH, acids or temperature (or bases
or high salt concentrations) the weak bonds holding the tertiary and the quaternary
structure gets disrupted so, that the protein unfold (into primary structure). This
unfolding is known as denaturation of proteins or loss of its functioning.
Denaturation is not strong enough to break peptide bonds thus, primary structure
remains unaffected.
A denatured protein may spontaneously refold into its original structure when
suitable condition are re-provided. This is called renaturation.
Polysaccharides
These are another class of macromolecule that are present in the acid insoluble
fraction. Polysaccharides are long chains of sugars. They are not sweet and are
insoluble in water. Polysaccharide chain (like glycogen) is made up of two ends,
whose right end is called reducing end and the other left end is called non-reducing
end. They- ace threads containing different monosaccharides as building blocks.
Types of Polysaccharides
Polysaccharides are of two types as given below
i. Homopolysaccharides
These are those complex carbohydrates which are formed by polymerisation of only
one type of monosaccharide monomers, e.g., Starch, glycogen and cellulose (these
all are composed of single type of monosaccharide unit namely glucose).