Why life chose Carbon?
It is the second most abundant element in the human body-18% of the wet weight. Molecules based on carbon-known as organic molecules because of their occurrence in living matter-constitute the majority of molecules found in living organisms from plants to people. 1 of the 4 special features of carbon is that carbon atoms are able to bond with each other to form extended chains-sharing pairs of electrons with neighbouring carbon atoms which allow the formation of stable covalent carbon-carbon bonds. Carbon can also form branched chains and rings- these structures help to provide the skeletons of organic molecules. Number of carbon atoms in the chain is important because this influences the size and the shape of molecules. Versatility of the carbon chains can contribute to the variety of molecules produced. A bare carbon atom skeleton can have little biological function. The second special feature of carbon is that it is able t form covalent bonds with other atoms. This allows a large number of functional groups to be formed and introduced into organic molecules. The functional groups provide different specific chemical properties to the molecules which contain them. The 3-D structure for which carbon provides the outline is fundamental to the specific nature of biological molecules. It is essential that molecules in the cell fit together correctly. The ability of two carbon atoms to form more than one bond with each other- a multiple bond is shorter and stronger than single bonds and also provides an additional way of introducing variety into the chemistry of organic molecules. Suitability of the C-C bond for building the molecules of life can be seen by comparing its bond energy with energy in sunlight. The energy present within the spectrum ranges from 170-270kj/ml of photons –insufficient to break double carbon bonds. IF this were not so, the light would break carbon compounds spontaneously so life as we know it would not exist....
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