Every living organism is made of chemicals which can be either elements or compounds. The elemental composition of living tissues is determined through elemental analysis and the chemical composition of organic compounds is determined through chemical analysis. All the carbon compounds we derive from living tissues are called biomolecules.
Biomolecules such as amino acids and sugars are also known as metabolites, because they are intermediates and products of metabolism. They are classified as primary and secondary metabolites. Compounds such as hydrogen, carbon, oxygen, nitrogen, sulphur and sodium are primary metabolites. On the other hand, compounds such as alkaloids, flavonoids, rubber, essential oils, antibiotics, coloured pigments, scents, gums and spices are secondary metabolites. Analysis of organic and inorganic constituents in a living tissue identifies functional groups such as aldehydes, ketones and aromatic compounds, also known as biomolecules.
The amino group and carboxylic group are present on the same alpha carbon atom of the amino acid. Hence, they are also known as α-amino acids. The four substituent groups of amino acids are hydrogen, the carboxyl group, amino group and a variable R group. A unique property of amino acids is the ionizable nature of the NH2 and COOH groups. In solutions, at a particular pH, ions with both positive and negative charges are equal. This form is known as the Zwitterionic form.
Fatty acids that form lipids have a carboxyl group attached to an R group. The R group could be a methyl, ethyl or a higher number of CH2 groups. When fatty acids combine with glycerol, they form esters, also known as glycerides. Lipids that contain phosphorous and a phosphorylated organic compound are known as phospholipids.
Living organisms also have many carbon compounds with heterocyclic rings such as adenine, guanine and thymine. These compounds are called nucleotide bases. When carbon compounds with heterocyclic rings are attached to a sugar, they are called nucleosides such as adenosine and thymidine. If a phosphate group is also found esterified to a sugar they are called nucleotides such as adenylic acid and thymidylic acid. Nucleotides make up the nucleic acids–DNA and RNA.