RNA DNA N H NH 胞嘧啶( cytosine,C NH 尿嘧啶( uracil,U 腺嘌呤( adenine.,A) 胸腺嘧啶( thymine,T) NH NH 鸟嘌呤( guanine,G)RNA N N N H N N H 2 腺嘌呤(adenine, A) N N H N H N N H 2 O 鸟嘌呤(guanine, G) 胞嘧啶(cytosine, C) N N H N H 2 O 尿嘧啶(uracil, U) N H N H O O 胸腺嘧啶(thymine, T) N H N H O O H 3 C DNA