Simply science: Quit fidgeting and read this column!
(Attention readers: To get the best effect from this article, you should read it as quickly as possible and jiggle one knee while reading.)
Quick! I’m in a hurry! What’s the most commonly consumed, mind-altering substance in the world?
Nope. Nope. Nope. It’s caffeine.
Perhaps you hadn’t thought of caffeine as a mind-altering substance. But, of course, it is. Why else would someone consume a normally very bitter-tasting compound if there was not some desired result?
More on that in a minute.
Unlike other drugs, which are scarce in the natural world and have to be laboriously and delicately extracted or created, caffeine literally grows on trees, and bushes, and some kinds of cacti, lily, holly and camellia. In fact, there are more than a hundred species of plants that produce caffeine molecules in their seeds, leaves or bark.
Hurry! Can you tell me how many species of plants manufacture nicotine or morphine? Just one each!
Human association with caffeine began a very long time ago. Different plants were discovered in many geographic regions of the world, and the use of them was widespread. Today, tea and coffee are the most popular drinks in the world. More tea is consumed, but coffee runs a close second.
However, in the U.S., soft drinks may surpass even coffee consumption. The “cola” in some soft-drink names comes from the “kola” bean found in Africa, and is used for caffeine extraction.
Caffeine is manufactured by plants from a precursor molecule called xanthine.
This chemical is widely distributed in nature. In animals it is used to manufacture DNA, and any excess is converted into uric acid and excreted.
But in plants xanthine acts a little like a convenient table on which to stack other things. One of the things plants stack on the xanthine table is a molecule called a methyl group.
If one methyl group is stacked on a xanthine table, it is called — drum-roll please — methylxanthine. But the table will support more methyl groups than one. So if the plant attaches a second group, the chemical is then called dimethylxanthine.
These names may not be as creative as some baby names, but they’re certainly descriptive.
Quick! Can you guess what we call a molecule with three methyl groups on the xanthine? Very good! Certain kinds of trimethylxanthine are also known as caffeine. (There are actually several variations of this molecule that have similar effects. For simplicity, however, I will just leave it there.)
But the layering makes caffeine kind of a lumpy, funny-shaped molecule, and that is important because the molecule must attach itself to another molecule in the cell membrane in order to alter cell function. The two have to fit together like a lock and key. This peculiar shape, then, makes caffeine highly selective and specific as to which cells are affected. It has hardly any effect on most cells of the body. But to the cells that have the matching molecule, it binds very tightly.
Excessive, but normal, neuronal stimulation of neurons while awake produces yet another molecule called adenosine. It binds to other neurons and slows neuronal firing. This keeps neuron activity within safe limits.
Caffeine mimics adenosine. When caffeine slips into adenosine’s place, it acts like a piece of wood under your brake pedal. Just as you can’t slow down the car, you can’t slow down the neuron activity. It doesn’t stimulate the neuron at all. It just blocks the brake. Your own natural neurotransmitters do the stimulating.
The group of cells that are most sensitive to the adenosine brake are found in a small area of the brainstem, but those cells fan out and connect to every other portion of the brain. That is why caffeine has a particularly broad, if difficult to predict, effect on people. It can cause the heart to beat more rapidly. It constricts some blood vessels, relaxes others, relaxes airways, and causes some types of muscle cells to contract more quickly.
Quick now! Which composer passionately loved coffee? His frenetic fugues most clearly capture the essence of the caffeinated experience.
Gary McCallister is professor of biology at Mesa State College.