An enzyme. Spirals and sheets and strands indicate different kinds of structures. (from Wikipedia)

Enzymes are the catalysts of the body, helping to facilitate chemical reactions that would be very slow or unfavorable in their absence. In a previous post, I discussed how platinum lowers the activation energy barrier for desirable chemical reactions in a car engine, among other places. Enzymes do the same thing, but they are much more selective. Platinum can act on millions of molecules. Enzymes are shaped so specifically that they act only on one molecule. Because of this, enzyme catalysis is often compared to a lock and key–only one chemical is so perfectly shaped as to fit into the active site of the enzyme.

Enzymes are mostly proteins, which are made of hundreds of amino acids with several layers of structure. Our DNA is coded so that enzymes can be assembled from the instructions. The “primary structure” is the sequence of amino acids strung together. The shape of local groups of amino acids gives the “secondary structure”; some combinations tend to coil, others tend to be flat (see the picture at the top of this post). This is due to interactions between the amino acid groups; for example, ionic groups might attract or repel each other. The “tertiary structure” is the structure of the overall molecule, also called the “folding”. We can reproduce the primary and secondary structures in the lab; the folding is harder, because for most sequences of amino acids, there are several possible structures. In the body, the protein is assembled in such a way that it conforms properly. We are mostly still unable to synthesize proteins and enzymes. We usually use bacteria and fungi to make them, when possible.

Enzymes are essential to life. They aid in digestion. Many diseases are caused by the lack of a single enzyme. People with lactose intolerance lack lactase; the deadly Tay-Sachs disease is caused by the lack of hexosaminidase A. In Tay-Sachs, a waste product of cellular metabolism builds up in the brain. Without the enzyme to accelerate its break-down, the waste product builds up to intolerable levels. We can obtain hexosaminidase A, but we can’t therapeutically deliver it to where it is needed in the brain.

You probably already knew that the human body is a remarkable machine. But I hope this brief overview of enzymes gives an appreciation for this one small aspect. Happy digesting.