The chemical method of extraction of biomolecules is done by using trichloroacetic acid (TCA). The sample like a piece of liver is properly grinded in TCA and filtered with the cotton cloth or cheese cloth. The acid insoluble fraction contains all the four major biomolecules (organic compounds) i.e., proteins, nucleic acids, polysaccharides and lipids. Further, using the tools of analytical chemistry, the molecular formula and structure of these substances can be deduced.
The acid-insoluble fraction has molecules of larger sizes like
nucleic acids: DNA and RNA
proteins
polysaccharides: glycogen, starch
lipids
Among all of these like nucleic acids, proteins, and polysaccharides, all are polymeric substances except the lipids. The polymeric substance means that the substance is composed of several monomers or repeating monomeric units. For example, proteins are made up of repetitive units of amino acids, nucleic acids are made up of nucleotides, polysaccharides of monosaccharides. Lipids are high molecular weight compounds but do not contain any of the repetitive monomeric units.