Q.Which set of elements together make up the overwhelming bulk of the dry weight of living tissue?

Biomolecules is the umbrella term for every chemical constituent of a living cell, and the first working distinction to draw is between micromolecules and macromolecules. If a tissue sample is ground in cold trichloroacetic acid (TCA) and centrifuged, the resulting acid-soluble pool contains micromolecules -- small compounds of low molecular weight, generally under about 1000 daltons, such as amino acids, monosaccharides, nucleotides, various lipids, vitamins and inorganic ions. The acid-insoluble fraction contains macromolecules -- large polymers such as proteins, polysaccharides and nucleic acids, built up by joining together many of the very micromolecules found in the soluble pool. Elemental analysis of any tissue shows that carbon, hydrogen, oxygen, nitrogen, phosphorus and sulphur, together with smaller essential amounts of elements such as sodium, potassium, calcium, magnesium and iron, make up the overwhelming bulk of its dry weight, while water accounts for 70 to 90 percent of wet weight and provides the medium for every cellular reaction. This macromolecule/micromolecule framework underlies the more detailed study, in turn, of proteins, carbohydrates, lipids, nucleic acids and enzymes.