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A call has gone through to 911: a few armed men are holding innocent
bystanders hostage during a bank heist. The police are on their
way, confident that the coating of spider silk they all wear will
protect them from flying bullets.
Spider silk? How would that stop bullets? That is the question that
UC Riverside Professor Cheryl Y. Hayaski and UC Santa Barbara biophysicist
Helen G. Hansma would like to answer. As of yet, spider silk is
just an annoyance to most of us. However, those sticky, stretchy
strands have quite a few interesting properties. For example, it
is stronger by weight than steel, and can stretch to ten times its
initial length. These properties make it a good material for possible
biodegradable bandages, artificial tendons, and yes, bulletproof
body armor.
There are several different types of spider silk, each with slightly
different protein structures. For the most part, linked sheets make
up the crystalline areas of the fibers. These sheets either have
polyalanine or polyglycinealanine backbones. Hydrophobic interactions
link the chains of the polyalanine sheets, which accounts for high
tensile strength. Due to the hydrophilicity of glycine, however,
such interactions are not possible in polyglycinealanine sheets,
resulting in lower tensile strength. In addition, the amino acid
sequence glycine-proline-glycine-x-x creates turns, which correspond
to higher extensibility. Flagelliform silk, which has 200% extensibility,
has at least 43 such turns in a row.
Due to the territorial nature of spiders, mass-production of the
silk is not possible—yet. Researchers are working on recombinant
DNA techniques to get bacteria to produce the necessary proteins.
In the meantime, avoid walking through spider webs—they will
not protect you from harm. All you’ll do is annoy a spider.
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