Biomacromolecules
There is one feature common to all those
compounds found in the acid soluble pool. They have molecular weights ranging
from 18 to around 800 daltons (Da) approximately.
The acid insoluble fraction has only four types of organic compounds i.e., proteins,
nucleic acids, polysaccharides, and
lipids. These classes of compounds with the exception of lipids have molecular weights in the range of
ten thousand daltons and above. For this very reason, biomolecules, i.e.,
chemical compounds found in living organisms are of two types. One, those which
have molecular weights less than one thousand daltons
and are usually referred to as micromolecules or simply biomolecules while
those which are found in the acid insoluble fraction are called macromolecules
or biomacromolecules.
The molecules in the insoluble fraction with
the exception of lipids are polymeric substances. Then why do lipids, whose
molecular weights do not exceed 800 Da, come under acid insoluble fraction,
i.e., macromolecular fraction? Lipids are indeed small molecular weight
compounds and are present not only as such but also arranged into structures
like cell membrane and other membranes. When we grind a tissue, we are
disrupting the cell structure. Cell membrane and other membranes are broken
into pieces, and form vesicles which are not water soluble. Therefore, these
membrane fragments in the form of vesicles get separated along with the acid
insoluble pool and hence in the macromolecular fraction. Lipids are not
strictly macromolecules.
The acid soluble pool represents roughly the
cytoplasmic composition. The macromolecules from cytoplasm and organelles
become the acid insoluble fraction. Together they represent the entire chemical
composition of living tissues or organisms.
In summary,
if we represent the chemical composition of living tissue from abundance point
of view and arrange them class-wise, we observe that water is the most abundant
chemical in living organisms.
Average
Composition of Cells
|
Component |
% of the total cellular mass |
|
Water |
70-90 |
|
Proteins |
10-15 |
|
Carbohydrates |
3 |
|
Lipids |
2 |
|
Nucleic acids |
5-7 |
|
Ions |
1 |
|
|
|
|
