How cells JUST KNOW

Domino by Bro. Jeffrey Pioquinto on flickr

Domino by Bro. Jeffrey Pioquinto on flickr

When I was in fifth grade, we had a program come into our classroom and teach us about the birds and the bees. We were told it was a very open environment and that we shouldn’t be afraid to ask any questions. Ask anything you want! they said. There are no silly questions. We each wrote a question on a slip of paper and handed it in.

The coordinators then read each question and answered them carefully. Kids asked about various body parts, rites of passage, weird dreams, and strange feelings. Then my question was read aloud: how do the sperm know where to go to find the egg? That’s right. Out of all the things about puberty and reproduction that confused me, I needed to understand how sperm KNOW where to find the egg. I knew that they didn’t have brains, so like, how did they KNOW what to do?!

The two women leading the program read the question aloud and laughed. They laughed! At my supposedly non-silly question! Then they explained that it’s probably like a stream and it just leads them to the egg. Besides being mortified that my question was laughed at, I wasn’t very satisfied with the answer.

Fifteen years later, after countless biology classes and the near completion of a PhD, I think I can provide a better answer to my own question. Cells don’t have brains, but they do have ways of sensing cues and responding to them, just like we can read a street sign and know where to turn. These cues come in the form of molecules of all types – chemical, protein, fat, sugar, or a combination. Once a molecular cue is picked up, a series of consecutive reactions will occur, like dominoes cascading down in a row. The end result of the chain reaction is the cell’s response to the original cue.

Actually, it’s a lot like this:

The cue is the car that starts it all off. The response is the band getting splattered with paint. None of the bowling balls, umbrellas, mannequins or pieces of confetti KNOW when or where to go, they are simply prompted to do so by the preceding reaction. This is how cells (like sperm cells) know exactly what to do, at exactly the right time.

And to all you fifth graders who have SILLY questions about how the world works, don’t give up on your inquisitiveness. You might find the answer you’re looking for down the road.