"What the molecules were doing before they're captured was a mystery and a matter of speculation," Stein said. "And we'd like to know because if you're trying to engineer something to control that molecule to get it to do what you want it to do you need to know what it's up to."
To find out what those molecules are up to, the researchers carefully tracked over 1,000 instances of a molecule zipping through a nanopore. The electric current through the pore provides a signal of how the molecule went through. Molecules that go through middle first have to be folded over in order to pass. That folded configuration takes up more space in the pore and blocks more of the current. So by looking at differences in the current, Stein and his team could count how many molecules went through head first and how many started somewhere in the middle.
The study found that molecules are several times more likely to be captured at or very near an end than at any other single point along the molecule.
"What we found was that ends are special places," Stein said. "The middle is different from an end, and that has a consequence for the likelihood a molecule starts its journey from the end or the middle."
Always room for Jell-O
As it turns out, there's an old theory that that explains these new experimental results quite well. It's the theory of Jell-O.
Jell-O is a polymer network a mass of squiggly polymer strands that attach to each other at random junctions. The squiggly strands are the reason Jell-O is a jiggly, semi-solid. The way in which the polymer strands connect to each other is not unlike the way a DNA strand connects to a nanopore in the instant it's captured. In water, DNA molecules are jumbled up in random squiggles much like the gelatin molecules in Jell-O.
"There's some powerful theory that describes how many ways the polymers
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