NH2 NH 腺嘌呤(adenine,A) 嘌呤(purine) NH NH NH2 鸟嘌呤(guanine,.G) 14 嘌呤(purine) N N NH N 1 2 3 4 5 6 7 8 9 N N NH N NH2 腺嘌呤(adenine, A) N NH NH N NH2 O 鸟嘌呤(guanine, G) 14