The family of isomerases differ in function and the organisms they function in; however, the reactions they catalyze are still similar. Isomerases rearrange the atoms within the molecule to form an isomer. Many of these molecules are used to allow their biosynthetical processes to proceed. Chalcone isomerase functions in plant flowering cells in the flavonoid process. This molecule is used to help with flowering. Mandelate racemase is used specifically by a bacteria Pseudomonas putida in its biosynthetic processes. The last example of isomerases is DNA topoisomerase 1. It is found in the nucleus of eukaryotes and in the cytosol of bacteria. This enzyme changes the topology of DNA to allow it to unwind and help in the replication process. All three of these examples change there molecule in some way to form a new molecule to be used in later processes. Although many of the active sites are different, each one of the examples uses hydrogen bonding and electrostatic interactions to bring in their ligand. Also the topology of each isomerase is a little different, but still contains both alpha-helices and beta-sheets. The contrast is how these are folded and put together to form the enzyme. There are many differences between the examples, but still there are some similarities in the reactions, active sites and topology. Each one of these enzymes allows their biosynthetic pathway to move forward. Without isomerases many processes would not be able to proceed because the isomeric form of a molecule would not be made.