[单项选择]______ any film before, his first attempt was a great success. A. Though having never directed B. Despite he had never directed C. As he had never directed D. In spite of his never having directed
第27题: [单项选择]下列关于肽键性质和组成的叙述正确的是( )。 A. 由CO和C-COOH组成 B. 由Ca1和Ca2组成 C. 由Ca和N组成 D. 肽键有一定程度双键性质 E. 肽键可以自由旋转 参考答案:D 答案解析:[解析] 氨基酸分子之间通过去水缩合形成肽链,在相邻两个氨基酸之间新生的酰胺键称为肽键。若许多氨基酸依次通过肽键相互连接,形成长链,称为多肽链。肽链中的游离氨基的一端称为氨基末端(N-末端);游离羧基