What is the difference between isomers?

There are optical isomers where the molecule contains a chiral center, usually a carbon atom with four different groups attached to the four corners of the tetrahedron. If the groups are A, B, C and D, then there are two different versions of the molecule. Looking down from the direction of group D, the other groups can be positioned as A, B, C or C, B, A. The two shapes have the same relationship as the left and right gloves. Many biological molecules exist only naturally in one configuration, although the opposite shape can be created synthetically.