Biomacromolecules

Every compound in the acid-soluble pool has a molecular weight between 18 and about 800 daltons (Da).

The acid-insoluble fraction holds only four kinds of organic compound: proteins, nucleic acids, polysaccharides and lipids. Except for lipids, these have molecular weights of ten thousand Da and more.

Biomolecules therefore fall into two groups: micromolecules (or simply biomolecules), under one thousand Da, and macromolecules (biomacromolecules), found in the acid-insoluble fraction.

Apart from lipids, the molecules of the insoluble fraction are polymers.

Lipids, whose molecular weights do not go beyond 800 Da, still come down in the insoluble fraction. Grinding breaks the cell membrane and other membranes into pieces that form water-insoluble vesicles, and these separate out with the insoluble pellet. Lipids are not strictly macromolecules.

The acid-soluble pool roughly represents the composition of the cytoplasm; the macromolecules of the cytoplasm and organelles form the acid-insoluble fraction. Together they are the whole chemical make-up of a tissue.

Water is the most abundant chemical in living organisms. Average share of total cell mass: water 70–90%, proteins 10–15%, nucleic acids 5–7%, carbohydrates 3%, lipids 2%, ions 1%.