February 27, 2008 | David F. Coppedge

Why Blood Clots Are Stretchy

A team of biophysicists at University of Illinois ran a computation for six months to find out why blood clots are stretchy.  The primary protein in the clot, fibrinogen, can stretch two to three times its resting size.  By studying the force on every atom in the protein, Science Daily said, they produced a force curve that matches the force measured on actual fibrinogen.
    Understanding clotting is important, because “Blood clots can save lives, staunching blood loss after injury, but they can also kill,” the article began.  “Let loose in the bloodstream, a clot can cause a heart attack, stroke or pulmonary embolism.”  It is important for clots to be elastic because “they have a mechanical function to withstand blood pressure.”

Tots learn from their mommies that their scratches will heal, so they don’t need to worry about being scarred for life.  We grew up accepting that as a given.  Imagine, though, having every scratch or cut from our youth a permanent disfigurement or point of blood leakage.  We would be covered head to toe in bandages as adults.  The life of hemophiliacs illustrates the point: when the blood clotting process breaks down, even a small cut is life-threatening.
    Imagine, furthermore, that clots were as hard as bone.  You would have to sit quietly for weeks till the wound was entirely healed, or else risk having changes in blood pressure rip it away from the surrounding tissue.  Instead, fibrinogen is constructed with coiled coils of amino acids to give it both strength and flexibility.  The network of fibers and proteins that form at a wound site involves multiple rounds of signaling, aggregating ingredients in the right order, and applying patches that won’t break off and cause a heart attack or stroke.
    Michael Behe argued in his classic book Darwin’s Black Box that the blood clotting cascade is irreducibly complex.  His argument didn’t take much convincing.  All he had to do was show a flowchart of the 25 or so components that interoperate with feedback and feed-forward procedures to ensure that the flow of blood is stopped quickly and safely.  If any one of these ingredients is missing, the system breaks.  Any question why this article here did not mention evolution?

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