A catalyst, or a chemical that makes things happen and speeds up the action, but without being changed itself in the process. Enzymes are proteins that perform a special function in the organism; they act as “organically grown” catalysts to launch chemical reactions that either form new chemical bonds or break down old ones between different chemical molecules. Enzymes do this by reducing and weakening the energy barrier that normally exists between atoms, a barrier that prevents or delays these atoms from forming a bond with each other. Thus, enzyme-catalyzed reactions in our bodies are much faster than the same chemical reactions produced in test-tubes.

The sequencing of amino acids determines how the protein folds into its three-dimensional structure, which is critically important in determining its catalytic function. Enzymes are highly specialized. Thousands of different enzymes are needed to act upon the thousands of different molecules that exist within a living cell. Any old enzyme won’t do! In order to perform its specialized job as a catalyst, a specific enzyme must move (or transport) to the particular place it was designed to occupy – that is, the place where the particular molecules it was designed to serve come together to form a bond.

If a mutation or permanent change occurs in the gene that determines the structure of an enzyme, the enzyme may become dysfunctional or defective and fail to perform its job. Though mutations are sometimes random and spontaneous, they can also be caused by environmental factors, such as exposure to radiation or certain kinds of chemicals. (Remember those mutant action heroes like the X-Men and the Teenage Mutant Ninja Turtles!)

So, let’s suppose (or hypothesize) that one of the MAO enzymes were designed to oxidize serotonin (or chemically transform this mood-regulating substance by combining it with oxygen). If something goes wrong with the enzyme, either because of a random, spontaneous mutation or because some adventurous scientist purposely knocks it out to see what will happen, then that enzyme won’t be able to perform its job – it won’t oxidize serotonin. If serotonin levels increase, aggression will also likely increase.