The living cells or organisms are composed of plenty of organic and inorganic compounds. Inside the cells, they have a specific compartments or structures, either membranous or non-membranous, performing typical functions. These are called as organelles which means little organ. Besides organelles, cells also have small or big-sized molecules. All these kinds are typically involved in the particular chemical reactions inside the body and the sum of all these reactions constitutes the metabolism.
During the chemical analyses of cells, they are properly grinded in trichloroacetic acid. Grinded tissues are filtered with the cotton cloth or cheesecloth. This results into two fractions (1) acid-soluble pool or filtrate and (2) acid-insoluble pool or retentate.
The filtrate contains several organic and inorganic chemical compounds. These compounds are smaller in size and usually forming the cytoplasmic composition of cells.
In contrast, the retentate or acid-insoluble pool or fraction contains (i) larger molecules and (ii) cell organelles or broken pieces of cell membrane and organelles. The larger or macromolecules includes nucleic acids DNA and RNA), proteins, polysaccharides and lipids.
Together, the acid-soluble and acid-insoluble pools represent the entire chemical composition of cells. The abundance (comparing to the total cellular mass) of various chemicals can be classified as
- water (60-90%)
- proteins (10-15%)
- nucleic acids (5-7%)
- carbohydrates (3%)
- lipids (2%)
- ions (1%).