All those compounds found in the acid soluble pool have molecular weights ranging from 18 to 800 daltons (Da).
The acid insoluble fraction, has only four types of organic compounds i.e., proteins, nucleic acids, polysaccharides and lipids. They have molecular weights in the range of ten thousand daltons and above with the exception of lipids.
For this very reason, biomolecules, i.e., chemical compounds found in living organisms are of two types, (i) macromolecules molecular weights less than 1000 daltons (ii) Biomacromolecules found in acid insoluble fraction and molecular weights is more than thousand dalton. Lipids are indeed small molecular weight compounds and 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.
These membrane fragments in the form of vesicles get separated along with the acid insoluble pool and hence in the macromolecular fraction.
Together they represent the entire chemical composition of living tissues of 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.
