Talk:Organic chemistry

This section, cut from Life might usefully be incorporated here?Gareth Leng 03:48, 10 April 2007 (CDT)

Why the central place of carbon in the chemistry of all earth’s living things? The physical chemistry of carbon allows it to bond with many other elements, especially hydrogen, oxygen, nitrogen and phosphorus, and, even to form carbon-to-carbon bonds. The avidity for carbon to bond to itself accounts for the formation of organic macromolecules since these different carbon bonds vary in strength as well as in 3-D conformation - but are all remarkably stable. Carbon atoms easily join into longer chains and closed rings; and the small organic molecules (such as sugars, amino acids and nucleotides) can join into huge macromolecules.

Due to the versatility of covalent bonding that exists for carbon at standard conditions a variety of large and dynamic organic molecules are possible. The standard set of bonds that carbon can form is that of a tetrahedron, or pyramid. Other types of bonds involve more than one shared electron, and for that reason are called double, and triple bonds; importantly, these different bonds constitute three entirely different geometries. Changing from one type of carbon-to-carbon bond to another type, as when a double bond is reduced to a single bond, will cause energy changes but without destroying the molecule. Such changes not only affect free energy, but also affect the actual shape of the molecule and the particular side groups attached to it. In this way, for at least some organic molecules, the "pulse of life" is represented at an atomic level.

These properties of carbon mean that organic macromolecules are capable of containing tremendous banks of information coded in their very structure. Not only can each of the constituent molecules be huge, but several categories of chemicals, like nucleotides or amino acids, that contain several different species, can be ordered such that the possible combinations are effectively limitless. All these molecules are involved in the molecular-interaction networks of cells. Included among those networks of interactions are those that enable cells to import and transform energy and energy-rich matter from the environment and that ultimately enable cells to grow, survive and reproduce.

Are there any other ways to make complex molecules with similar versatility? Yes, by using silicon — carbon's close relative on the periodic table. But whereas the bonds of carbon are very stable at the temperatures that are compatible with life as we know it, silicon's Si-Si bonds are much more likely to disassociate. That is not true at much higher temperatures, and so it is possible to imagine biochemical reactions, more or less as we know them, occurring at, say, 400 degrees Celsius with silicon taking the place of carbon. If they do, one would expect that they too would be able to form structures of such variation in size, shape, charge and composition, that their very existence provides ordered information.