C HAPTER . How to Analyse Chemical Composition? . Primary and Secondary Metabolites .
Biomacromolecules . Proteins . Polysaccharides . Nucleic Acids .
Structure of Proteins . Enzymes In higher classes you will learn about how to analyse a living tissue sample and identify a particular organic compound. It will suffice to say here that one extracts the compounds, then subjects the extract to various separation techniques till one has separated a compound from all other compounds. In other words, one isolates and purifies a compound.
Analytical techniques, when applied to the compound give us an idea of the molecular formula and the probable structure of the compound. All the carbon compounds that we get from living tissues can be called ‘biomolecules’. However, living organisms have also got inorganic elements and compounds in them. How do we know this?
A slightly different but destructive experiment has to be done. One weighs a small amount of a living tissue (say a leaf or liver and this is called wet weight) and dry it. All the water, evaporates. The remaining material gives dry weight.
Now if the tissue is fully burnt, all the carbon compounds are oxidised to gaseous form (CO , water vapour) and are removed. What is remaining is called ‘ash’. This ash contains inorganic elements (like calcium, magnesium etc). Inorganic compounds like sulphate, phosphate, etc., are also seen in the acid-soluble fraction.
Therefore elemental analysis gives elemental composition of living tissues in the form of hydrogen, oxygen, chlorine, carbon etc. while analysis for compounds gives an idea of Element % Weight of Earth’s crust Human body Hydrogen (H) . . Carbon (C) .
. Oxygen (O) . . Nitrogen (N) very little .
Sulphur (S) . . Sodium (Na) . .
Calcium (Ca) . . Magnesium (Mg) . .
Silicon (Si) . negligible * Adapted from CNR Rao, Understanding Chemistry , Universities Press, Hyderabad. T ABLE . A Comparison of Elements Present in Non-living and Living Matter* Component Formula Sodium Na + Potassium K + Calcium Ca ++ Magnesium Mg ++ Water H O Compounds