The living matter is composed of mainly six elements: carbon, hydrogen, oxygen, nitrogen, phosphorus and sulphur. These elements together constitute about 90% of the dry weight of the human body. Chemicals or molecules present in the living organisms are known as biomolecules. Depending upon their weight and solubility biomolecules fall into two categories: micromolecules and macromolecules. Micromolecules may be inorganic or organic and include water gases, minerals, sugars, amino acids, and nucleotides. Macromolecules generally belong to four classes of organic compounds: carbohydrates, lipids, proteins and nucleic acids.
