Isomers are compounds that have the same molecular formula but different structural formulas. Stereoisomers are isomers that have the same sequence of bonded atoms, but they differ in their three dimensional orientation in space. [pic]
shown above is an example of the two types of Stereoisomers;
Enantiomers, which are stereioisomers which are non-superimposible mirror images, much the same as one’s left and right hands are the same apart from the fact they have opposite orientation.
Diastereomers, which are stereoisomers that are not Enatiomers, they occur when two or more stereoisomers of a compound have different configurations at one or more, (but not all) of the stereocenters and are not mirror images.
Stereochemistry , may seem trivial at times due to the differences between stereoisomers being so subtle. However in nature, and more importantly, in a biological system such as the body, the subtle differences have wide sweeping implications. In living organisms chiral molecules are usually present in only one of their chiral forms. For Example the amino acids that make up proteins are only found as their L iosmers whereas glucose only occurs as its D isomer. Evolution has played a large role in this fact by favouring one isomer over the other. This concept is easier to comprehend when you remember that the molecules that select an isomer to use (invariably proteins) are themselves isomers. Therefore it is not surprising that they have a ‘built in bias’. Thus, it can be said that isomer are important due to the fact that our entire biology, and that of every organism on the planet, is built on them.
Biological interations between molecules are stereospecific, The ‘fit’ in such interations must be correct. A good example of this is the ‘Lock-and-key’ and induced fit models for enzyme function. Enzymes are very specific only operating on substrate that accurately fits the shape of...