托福阅读材料之丝绸

　　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.

　　蚕丝是史上全世界最强韧的天然纤维。长久以来，科学家想知道蚕如何产丝，然后仿效制丝过程，生产高强高性能的运动原材及执法材料。

　　虽然我们对制丝的整个过程了解的不多，但是科学家可以肯定关键在于蚕如何细心掌控丝腺里的水分。

　　蚕丝的高强性是因为蛋白质。蛋白质部分是亲水的;部分是疏水的。蚕吐丝前，蛋白质尚未结晶，蚕是如何将蛋白质转换成蚕线一直是个未解之谜。而过早的结晶会阻塞丝腺，蚕很可能为此丧命。

　　奥秘在于丝腺里的水分逐步流失，而蛋白质可以储存水分，蚕在吐丝前先溶解于水。水分渐渐流失，亲水的蛋白质丝丝缕缕缠绕在一起，将疏水的部分也裹在一起。

　　水分继续流失，包裹在一起的蚕丝像滚雪球般形成凝胶状。亲水的蛋白质始终储存足够水分避免过早结晶。结晶后，蚕吐出蚕丝。

　　fiber：纤维

　　convert：转换

　　spin ： (蚕)吐丝;过去式spun或 span 过去分词spun 现在分词spinning

　　fatal:致命的