Natures wonders: Spider silk amazing stretch (Introduction)

by David Turell @, Monday, February 15, 2016, 15:36 (1313 days ago) @ David Turell

Spider silk can stretch up to five times its length:

http://phys.org/news/2016-02-big-spider-silk-proteins.html

"While working to improve a tool that measures the pushes and pulls sensed by proteins in living cells, biophysicists at Johns Hopkins say they've discovered one reason spiders' silk is so elastic: Pieces of the silk's protein threads act like supersprings, stretching to five times their initial length.

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"'All other known springs, biological and nonbiological, lengthen in a way that is directly proportional to the force applied to them only until they have been stretched to about 20 percent of their original length," notes Taekjip Ha, Ph.D., the study's lead researcher. "At that point, you have to apply more and more force to stretch them the same distance as before. But the piece of the spider silk protein we focused on continues to stretch in direct proportion to the force applied until it reaches its maximal stretch of 500 percent."

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"The Virginia team set up those experiments by inserting a repeating amino acid sequence—taken from the spider silk protein known as flagelliform—into a human protein called vinculin. Vinculin is responsible for internalizing forces outside a cell by bridging the cellular membrane and the actin network within the cell, making it an important mechanical communicator within the cell.

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"The team wasn't expecting the spider silk inserts to show such linear behavior because, according to Ha, they don't form well-defined, three-dimensional structures. "Usually, unstructured proteins show disorderly, nonlinear behavior when we pull on them," says Ha. "The fact that these don't act that way means that they will be really useful tools for studying protein mechanics because their behavior is easy to understand and predict.'"

Comment: I've skipped the details of how they made the measurements. The key point is that these proteins are showing very unusual properties, helpful to spider webs. Again in evolution, how did the spider find these protein molecules that are so different. Not by chance if the spider had to depend on a useful web for food that didn't work properly. Spiders might have starved to death waiting for the right protein. Design is an answer.


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