题目

某外毒素为环状肽，结构式如图所示，请据图回答下列问题： （1） 该化合物中含有个游离的氨基，个游离的羧基。 （2） 该化合物是由个氨基酸组成的，其中有个氨基酸的R基相同，这个R基是。 （3） 该化合物含有个肽键。 （4） 该外毒素在环状肽形成过程中失去了个水分子，相对分子质量减少了。 （5） 填写虚线框内结构的名称：A．，B．(从氨基酸结构通式的角度讲)。Dear Jack,How are you? I have been in the USA for six months. I like the life here. I have a few friends. I don’t have much homework. There are a lot of sports at my school, but I don’t like sports at all. I like the food very much. I eat a lot of different kinds of food every day. I like coke（可乐）very much. I don’t drink water. I drink coke instead（代替）. I’m enjoying my life here. The sad thing is that sometimes I get ill. I don’t know why. My parents say I must go on a diet and do more sports. Must I? Yours, David【小题1】 David has been in America for six months.【小题2】 David has to do much homework.【小题3】There are many sports at David’s school.【小题4】David likes coke better than water.【小题5】David knows why he is often ill.