B-Keratin-D-AMCB

http://www.nyhallsci.org/marvelousmolecules/marveloussub.html <    http://www.open2.net/sciencetechnologynature/worldaroundus/silk.html>

Silk, or beta-keratin, is a natural polymer made from the repeating proteins GLY-SER-GLY-ALA-GLY. Natural silk is produced by silkworms and spiders, among other organisms. Scientists have learned how to make synthetic forms of silk by taking and studying samples of this natural polymer. Synthetic silk is made from nylons, which are bound tightly together to become stronger. Natural silk consists of 30-40 percent polymers, while the rest is water. Spiders are capable of synthesizing these polymers into strong, insoluble fibers. Once the silk has dried, it cannot return to a liquid state, and it forms small crystalline structures to help prevent the fibers from tearing. Engineered nanoparticles serve the same purpose in synthetic silk.

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The pr ocess by which beta keratin monomers are linked together is called dehydration condensation. This means that two hydrogen atoms and one oxygen atom are removed to form water, while the other atoms come together to form the fibrous material known as silk.  [|http://www.biology-blog.com/blogs/archives/Animal-science-blog/197525293-Nov-18-2006.html

Spiders create more than one type of silk, depending on the purpose it is going to serve. The Argiope Argentata, for example, can create up to five different types of silk, each serving a different purpose. The silk is created through their silk glands, in the form of an aqueous solution. The silk is then put through spinnerets, which are usually in pairs. The ampulla then stores the newly created fibers, and the spinning duct removes any excess water from the fibers while also assisting in the silk's formation. This is followed by lipid secretions, which take place at the end of the duct. The fibers then go to the valve, which assists in repairing broken fibers. Finally, various compounds are added to enhance the fiber's properties, such as making it acidic so it is protected from fungi that would otherwise eat the proteins. After this process, the silk is finally released.

The general trend for protein sequences in spider silk alternates between glycine and alanine, or repeating sequences of alanine alone. These sequences assemble themselves into beta pleated sheets, which stack to form the crystalline structures on the surface of the silk. The other sequences of proteins form amorphous domains, which give the silk its elacticity. Interchain H-bonds are formed while side chains are formed below and above the plane of the H-bond network. The combination of the crystalline structures and the amorphous domains give silk very unique and powerful properties. 

Silk fibers have triangular cross-sections with rounded corners, which allows light to hit it at many different angles and is responsible for silk's natural shine. The elasticity in spider silk is very high; it can stretch up to 40% from it's original length without tearing. It is tougher, has a higher elasticity, and is more waterproof than silkworm silk. In fact, absorbing water helps strengthen silk webs, as the more water it absorbs the less brittle and likely it is to break. Natural silk is also very strong, able to be compared with many manmade fibers such as kevlar. Spider silk is five times stronger than a sample of steel of the same diameter, and in theory a Boeing 747 could be stopped mid-flight by a pencil-width strand. It is also capable of retaining its strength below -40°C.

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Synthetic silk has the same set of chemical properties as natural silk. It is still a beta keratin with hydrogen bonds and crystalline structures to help reinforce it. It is in the real of physical properties that it differs from natural silk. Synthetic silk is very lustrous and smooth, and handle dyes very well. Like natural silk, synthetic silk is very resistant to abrasions. The unique properties of silk can also seemingly change with the seasons. In the summer it keeps the wearer cool, while in the winter it keeps the wearer warm. It is also a very flexible material; a silk scarf can be pulled through a wedding ring and in a matter of seconds it will retake its original form without much wrinkling. Synthetic silk also has some elasticity, although not as much as natural silk. It will retain its shape as long as it is not stretched beyond 20-25% of it's original length. It can also absorb a surprising amount of moisture before it begins to feel wet, much like spider silk. 

Natural silk possesses highly important uses for the organisms that create it, such as silkworms and spiders. The uses are quite obvious as well: Spiders utilize it for webbing, while silkworms use it for cocoons. Of course, synthetic silk wouldn't exist if scientists did not study samples of the real thing, so natural silk also contributed, and continues to contribute to the science of replicating silk. Studying the molecular build of the silk allows scientists to better understand how to replicate it, and some are even endeavoring to try and improve synthetic silk past the properties of the natural polymer.

Synthetic silk, because of its light weight and versatility in weather, provides excellent for clothing. Some articles of clothing that are made from synthetic silks are shirts, dresses, underwear, pajamas, and blouses, among others. It is not only used for clothing, but for rugs, upholstry, bedding, and wall hangings as well. The uses of synthetic silk don't stop at decor, however. Before kevlar, early bulletproof vests were made from silk until around the time of World War I. It can also be used as non-absorbable surgical sutures, and Chinese doctors have used it in the process of crafting artificial arteries. Silk was and is quite the life-saver.  http://www.indiaplaza.com/homeanddecor/ls.aspx?c=962

   Works Cited:  Ballenberger, Walt. Ballenberger, Linda. "Properties and Characteristics of Silk." __Ezine Articles__. 14 March 2007. 14 May 2008.  http://ezinearticles.com/?Properties-and-Characteristics-of-Silk&id=488797   Elices, Manuel. **     José Pérez-Rigueiro, Gustavo R. Plaza, and Gustavo V. Guinea. "Finding inspiration in Argiope Trifasciata Spider Silk Fibers." __TMS__. February 2005. 14 May 2008. http://www.tms.org/pubs/journals/JOM/0502/Elices-0502.html

**    Massachusetts Institute of Technology. "Engineers Probe Spiders' Polymer Art: Manufactured Silk Could Be Used For Artificial Tendons, Parachutes, More." __ScienceDaily__ 1 November 2006. 16 May 2008. http://www.sciencedaily.com/releases/2006/10/061030183133.htm

  "Spider Silk: Properties, uses, and production." __University of Bristol__. 14 May 2008. [|http://www.chm.bris.ac.uk/motm/spider/page2.htm    "Silk." __Wikipedia: The Free Encyclopedia__. 14 May 2008. http://en.wikipedia.org/wiki/Silk

"Spider Silk." __Wikipedia: The Free Encyclopedia__. 14 May 2008. <  http://en.wikipedia.org/wiki/Spider_silk>