General ---------Biology ------------------Online------------------   ----wilcox@sunline.net Ch.  2 :  The Chemical Context of Life

Endorphins, as an example, are molecules naturally produced in the body that in some way trigger the perception of pleasure by the brain.  Endorphins are produced when we eat, exercise vigorously, engage in sex or "bond" with another creature.  Endorphins are produced by all vertebrate animals and contribute to survival of a species by rewarding certain critical behaviors with pleasure. 

Certain nerve cells in the brain produce endorphins.  Other adjacent cells receive these endorphins and trigger the perception of pleasure.  The endorphin must travel a short distance across a synapse, a space between the transmitting cell and the receiving cell, and collide with a receptor molecule embedded in the surface of the receiving cell.  The endorphin's shape fits perfectly into a cavity in the endorphin receptor molecule, like a lock and key. Like a key, if the shape of the incoming molecule is just a little off, it won't fit perfectly, and it will not trigger a response by the receiving cell.

The figure below illustrates the overall shape of an endorphin.  The actual portion that fits into the receptor in shown by the rectangle.  Notice that morphine has a portion with an identical shape.  Both molecules owe their exact shape, in part, to "hydrogen bonds."

Summary: You should understand 

• organic molecules produce their effects by "reacting" with other molecules
• endorphin and endorphin-receptor molecules are an example
• shape is important because to react the molecules must "fit" together
• the lock and key analogy is a good one
• a molecule's shape is influenced by the location and number of "hydrogen bonds"