托福閱讀材料之絲綢

　　Silk is the strongest natural fiber in the world, as far as we know. Scientists long to understand just how exactly the silkworm manages the process of silk weaving, so they can replicate the process in order to manufacture such things as high-strength and high-performance materials for sports and law enforcement.

　　Though our understanding of the silk-making process is not yet complete, scientists do know that the key to making silk lies in the animal’s careful managing of the water content in its silk glands.

　　Silk gets its strength from its proteins. Parts of the proteins are hydrophilic, or water-loving; and parts are hydrophobic, or water-fearing. For some time it was a mystery how silkworms managed to convert these proteins into silk threads without the proteins crystallizing before the animal is ready to spin them. Premature crystallization would clog up their silk glands, which would likely prove fatal to the little creatures.

　　The answer lies in the silkworm’s slowly decreasing the water content in its silk glands and in the proteins’ ability to retain water, keeping the solution soluble up until it is spun. As the water decreases, the water-loving parts of the proteins fold together in chains, forcing the water-fearing parts together.

　　As the water level continues to drop, the folded chains of silk push together more and more to form larger and larger gel-like structures. All the while the water-loving parts retain enough water so that the solution does not crystallize prematurely, before there is enough of the material to begin spinning.

　　蠶絲是史上全世界最強韌的天然纖維。長久以來，科學家想知道蠶如何產絲，然后仿效制絲過程，生產高強高性能的運動原材及執(zhí)法材料。

　　雖然我們對制絲的整個過程了解的不多，但是科學家可以肯定關鍵在于蠶如何細心掌控絲腺里的水分。

　　蠶絲的高強性是因為蛋白質。蛋白質部分是親水的;部分是疏水的。蠶吐絲前，蛋白質尚未結晶，蠶是如何將蛋白質轉換成蠶線一直是個未解之謎。而過早的結晶會阻塞絲腺，蠶很可能為此喪命。

　　奧秘在于絲腺里的水分逐步流失，而蛋白質可以儲存水分，蠶在吐絲前先溶解于水。水分漸漸流失，親水的蛋白質絲絲縷縷纏繞在一起，將疏水的部分也裹在一起。

　　水分繼續(xù)流失，包裹在一起的蠶絲像滾雪球般形成凝膠狀。親水的蛋白質始終儲存足夠水分避免過早結晶。結晶后，蠶吐出蠶絲。

　　fiber：纖維

　　convert：轉換

　　spin ： (蠶)吐絲;過去式spun或 span 過去分詞spun 現(xiàn)在分詞spinning

　　fatal:致命的