天然蛋白质中不含有的氨基酸是（）
A．半胱氨酸
B．鸟氨酸
C．蛋氨酸
D．脯氨酸
参考答案：B
解析：
GSH是由谷氨酸、半胱氨酸和甘氨酸组成的三肽，分子中的半胱氨酸巯基是其主要功能基团。(2)氨基酸是组成人体蛋白质的基本单位，体内20种氨基酸按理化性质分为4组：①非极性、疏水基酸；②极性、中性氨基酸；③酸性氨基酸；④碱性氨基酸。鸟氨酸不包括在其中。
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| When I was growing up, I had an old neighbor, Dr. Gibbs. He didn't look like any 1 I 2 . He never invited us to play in his yard,but he was a very 3 person. When Dr. Gibbs wasn't saving lives, he was planting trees. He owned a large field and wanted to make it a forest. The good doctor had some interesting ideas about planting trees. He never watered his new trees. Once I asked why. He said that watering plants spoiled them, and that if you 4 them, each baby tree would grow weaker and weaker, so you had to make things difficult for them and 5 the weaker trees early. He talked about how watered trees grew shallow (浅的) roots, and how trees that weren't watered had to grow deep roots in search of water 6 the earth by themselves. 7 roots were very important. So he never watered his trees. He'd planted an oak and, 8 watering it every morning, he'd beat it with a rolled-up newspaper. I asked him why he did that, and he said it was to get the tree's attention. Dr. Gibbs died several years 9 I left home. Every now and then, I walked by his house and looked at the trees 10 I watched him 11 about twenty-five years ago. They're very big and strong now. I planted some trees a few years later and carried water to them for a whole summer. After two years of 12 too much, whenever a cold wind blows in, they 13 a lot. Every night before I go to bed, I check on my two sons. Mostly I pray (祈祷) that their lives will be easy. But lately I've been thinking that it's time to change my prayer. I know my children are going to face difficulties. There's always a cold wind 14 somewhere, so 15 we need to do is to pray for roots that reach deep into the brave heart, so when the rains fall and the winds blow, we can face it strongly and won't be beaten down. | ||||
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