When applied to DNA, the Jell-O theory predicts that if you were to count up all the possible configurations of a DNA strand at the moment of capture, you would find that there are more configurations in which it is captured by its end, compared to other points along the strand. It's a bit like the odds of getting a pair in poker compared to the odds of getting three of a kind. You're more likely to get a pair simply because there are more pairs in the deck than there are triples.
This measure of all the possible configurations a measure of what physicists refer to as the molecule's entropy is all that's needed to explain why DNA tends to go head first. Some scientists had speculated that perhaps strands would be less likely to go through by the middle because folding them in half would require extra energy. But that folding energy appears not to matter at all. As Stein puts it, "The number of ways that a molecule can find itself with its head sticking in the pore is simply larger than the number of ways it can find itself with the middle touching the pore."
These theories of polymer networks have actually been around for a while. They were first proposed by the late Nobel laureate Pierre-Gilles de Gennes in the 1960s, and Bertrand Duplantier made key advances in the 1980s. Mihovilivic, Stein's graduate student and the lead author of this study, says this is actually one of the first lab tests of those theories.
"They couldn't be tested until now, when we can actually do single molecule measurements," she said. "[De Gennes] postulated that one day it would be possible to test this. I think he would have been very excited to see it happen."
|Contact: Kevin Stacey|