Stahler: Talking to yourself about a molecule of adrenaline
November 15, 2012
It's 100,000 years ago … you're walking through the tall grass, beneath the African sun.
A lion appears. A message goes out from your brain: "Brain to lungs!" … "Brain to heart!" … "Brain to muscles!" … "Get it in gear!!!"
The message I'm sending you now is composed of words.
If only I could draw, I could tell my story in pictures.
Our bodies — organs, tissues, cells — tell stories with sculpture: clumps of atoms – molecules – each clump shaped just so, each shape meaning something different.
Explore your cheek with your tongue and you're stroking the outer membranes of gazillions of living cells. Membranes keep the cells' machinery in, the environment out.
When messenger molecules — microscopic sculptures — arrive at a cell membrane, some slip right through to deliver their message. But many cannot. Adrenaline, for instance — the "Get it in gear!!!" hormone — is stuck outside.
Embedded within the cell membrane are other precisely-shaped sculptures, shaped just like adrenaline, only backwards: mirror-images of the adrenaline molecule. Where adrenaline bulges outward, they indent; where adrenaline indents, these membrane sculptures bulge out.
A molecule of adrenaline could snuggle nicely into its mirror-sculpture. But how to get it there?
Oil and water don't mix. Drizzle oil on water and the water pushes the tiny droplets together into larger ones.
Parts of the adrenaline molecule are oily. Our body fluids are watery. The watery fluids push the oily molecule toward its also-oily mirror-sculpture.
The adrenaline molecule fits nicely into its mirror-sculpture, like a key into a lock – a 3D jig-saw puzzle. But what's to prevent a similarly-shaped molecule from sliding in instead?
When you rub a balloon on your shirt, the balloon robs electrons from atoms in the shirt. The electrically-charged balloon will then stick to the wall via static electricity.
The same electrostatic force binds atoms together: Two atoms of hydrogen and one atom of oxygen stick together to form a molecule of water.
The electrostatic force also binds one molecule to another – it makes molecules sticky, holding glue molecules to paper, gum molecules to your shoe.
Electrostatic attraction makes adrenaline sticky … but only in certain places.
A balloon rubbed carefully, here but not there, might develop a charge here, but not there (I say "might" because I've yet to do the experiment … I'll report back). That's what the adrenaline molecule looks like: its surface is more positive here, more negative there.
Its mirror-image, embedded in the cell membrane, is also more positive here, more negative there … but, again, mirror-imaged to adrenaline.
Opposites attract. When the adrenaline molecule nestles into its mirror-sculpture – when it docks with its receptor – it's held like glue. Molecules with the wrong charge pattern would be pushed back out.
Even as the receptor pulls the adrenaline inward, the adrenaline molecule pulls back, pulling the receptor slightly out of shape.
That shape-change is transmitted, down the length of the receptor, through the membrane to the interior of the cell.
The shape-change carries the message. Once inside the cell, it triggers the cell to action. Billions of cells, so triggered, create an adrenaline rush.
Work that led to our current, still sketchy understanding of this lock-and-key, shape-change mechanism will be recognized in December with the award of the 2012 Nobel Prize in chemistry. Evolution has used the mechanism many hundreds of times, to carry myriad messages from the outside, in. The messages might flow from one brain cell to another, enabling our brains to think … might be carried by morphine … by caffeine … or by photons – particles of light – enabling our eyes, at this moment, to see.
Al Stahler's science programs can be heard on KVMR (89.5 FM). He teaches classes to students of all ages, and may be reached at firstname.lastname@example.org