题目：
下列氨基酸中无L型或D型之分的是（）
A.谷氨酸
B.甘氨酸
C.半胱氨酸
D.赖氨酸
E.组氨酸
答案：
参考答案：B
解析：天然氨基酸的结构具有的共同特点：即在羧基邻位α碳原子上有一个氨基，因此称α氨基酸。α氨基酸的碳原子上所连结的4个基团都不相同（除甘氨酸），4个基团的排列方式从三度空间看，有两种方式，互成立体异构体，分别称L型和D型。而甘氨酸α碳原子上连接有一个氨基、一个羧基，两个相同的氢原子，无法构成异构体，无L型和D型之分。故选B。
下列氨基酸中无L型或D型之分的是（） A.谷氨酸 B.甘氨酸 C.半胱氨酸 D.赖氨
来源：www.tikuol.com
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