NaCl, CaCO , PO SO − − , T ABLE . A List of Representative Inorganic Constituents of Living Tissues the kind of organic (Figure . ) and inorganic constituents (Table . ) present in living tissues.
From a chemistry point of view, one can identify functional groups like aldehydes, ketones, aromatic compounds, etc. But from a biological point of view, we shall classify them into amino acids, nucleotide bases, fatty acids etc. Amino acids are organic compounds containing an amino group and an acidic group as substituents on the same carbon i.e., the α -carbon. Hence, they are called α -amino acids.
They are substituted methanes. There are four substituent groups occupying the four valency positions. These are hydrogen, carboxyl group, amino group and a variable group designated as R group. Based on the nature of R group there are many amino acids.
However, those which occur in proteins are only of twenty types. The R group in these proteinaceous amino acids could be a hydrogen (the amino acid is called glycine), a methyl group (alanine), hydroxy methyl (serine), etc. Three of the twenty are shown in Figure . .
The chemical and physical properties of amino acids are essentially of the amino, carboxyl and the R functional groups. Based on number of amino and carboxyl groups, there are acidic (e.g., glutamic acid), basic (lysine) and neutral (valine) amino acids. Similarly, there are aromatic amino acids (tyrosine, phenylalanine, tryptophan). A particular property of amino acids is the ionizable nature of –NH and –COOH groups.
Hence in solutions of different pH, the structure of amino acids changes. B is called zwitterionic form. Lipids are generally water insoluble. They could be simple fatty acids.
A fatty acid has a carboxyl group attached to an R group. The R group could be a methyl (–CH ), or ethyl (–C H ) or higher number of –CH groups ( carbon to carbons). For example, palmitic acid has carbons including carboxyl carbon. Arachidonic acid has carbon atoms including the carboxyl carbon.
Fatty acids could