In globular proteins the
polypeptide chain is folded into a
compact spherical shape.
Fibrous proteins do not fold up
into a ball shape but remain as
longs chains.
The globular proteins are
soluble due to the hydrophilic
side chains that project from
the out side of the molecules
and are therefore important in
metabolic reactions.
The fibrous proteins are insoluble (hydrophobic) and
important structural molecules. Several
polypeptide chains can be cross-linked
for additional strength.
Haemoglobin is a globular protein. it
acts as an oxygen transport
molecule. It is made up of four
polypeptide chains, each is
associated with an iron-containing
haem group (grey). Oxygen attaches
to the iron with the haem group.
Because the protein is associated
with another chemical group it is
called a conjugated protein.
Collagen is a fibrous protein. Three
polypeptide chains wind around each other to
form a rope-like strand held together by
hydrogen bonds between the chains. Each
strand cross-links to other strands to produce
a molecule with tremendous strength.