$\rightarrow$ All those compounds found in the acid-soluble pool have molecular weights ranging from $18$ to $800$ Daltons (Da). These are known as micromolecules or biomolecules of low molecular weight.
$\rightarrow$ The acid-insoluble fraction contains four types of organic compounds: proteins, nucleic acids, polysaccharides, and lipids. With the exception of lipids, these have molecular weights in the range of $10,000$ Daltons and above. These are known as biomacromolecules.
$\rightarrow$ Biomolecules are classified based on their molecular weight: $(i)$ Micromolecules (molecular weight $ < 1000$ Daltons) and $(ii)$ Biomacromolecules (molecular weight $ > 1000$ Daltons).
$\rightarrow$ The molecules in the insoluble fraction, except for lipids, are polymeric substances.
$\rightarrow$ Lipids are small molecular weight compounds but are found in the acid-insoluble fraction because they form vesicles during tissue grinding, which are not water-soluble.
$\rightarrow$ 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 | $1$ |