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Saturday, November 11, 2006

Why is Snot Slimy?

Each string of mucus in your nose is a long molecule. Each of these strings has a bunch of smaller molecules called “neuraminic acid”, stuck all over it. Neuraminic acid has a negative charge. When all those negative charges interact, they repel each other, like pushing the south poles of two magnets toward each other so that the magnet poles slip away from each other. The negative charges on the neuraminic acid on the mucus strings slip away from each other when they are forced together, and so mucus feels slippery, or slimy.

Here’s another question; why does mucous have those neuraminic acids on it?

Neuraminic acid is a molecule is also on the surface (cell membrane) of your lung cells. The influenza virus (the flu virus, the coughing kind of flu, not the stomach flu,) attaches to neuraminic acid so it can infect your lung cells. Then, the virus slips inside your cells and shanghais your cells’ machines (enzymes and ribosomes) to make lots more flu viruses, until there are so many viruses that the cell explodes. Then those viruses infect other lung cells, and so on, and so on, and so on.

But mucus in your nose also has neuraminic acids all up and down it. Think of mucus as a long string of decoys to fool the flu virus. When a flu virus enters your nose, it latches onto the first thing it finds with a neuraminic acid on it, mucus. Then, you have the chance to get the mucus out of your nose, so the virus won’t infect you. Pretty neat defense, huh?

But the virus has a way around that defense.

The flu virus has an enzyme (a protein that does a job), called neuraminidase, which cuts its bond with the neuraminic acid if the virus can’t find a cell underneath the neuraminic acid. So, if you don’t blow your nose, the virus can cut itself free of the mucus, float into your lungs, and give you the flu.

Take home message: Blow your nose and wash your hands after you’ve been around someone who is sick.