核苷酸Nucleotide

碱基分为嘌呤（腺嘌呤 A、鸟嘌呤 G）和嘧啶（胞嘧啶 C、胸腺嘧啶 T、尿嘧啶 U）。碱基通过 N-糖苷键连接在糖的 C1′ 上（嘌呤用 N9，嘧啶用 N1），均为 β 构型。磷酸通常连在 C5′ 上，可有一个、两个或三个磷酸，分别记作 NMP、NDP、NTP。核酸中的核苷酸以 3′,5′-磷酸二酯键相连。

The bases are purines (adenine A, guanine G) and pyrimidines (cytosine C, thymine T, uracil U). Each is linked by a β N-glycosidic bond to C1′ of the sugar (through N9 for purines and N1 for pyrimidines). The phosphate is usually on C5′ and may be one, two or three units, written NMP, NDP and NTP. In nucleic acids nucleotides are joined by 3′,5′-phosphodiester bonds.

1880–1900 年科塞尔鉴定出核酸中的各种碱基。1909 年列文鉴定出核糖，1929 年又鉴定出脱氧核糖，并提出核苷酸是核酸的基本单位（但他错误地提出了“四核苷酸假说”）。1940 年代托德通过化学合成确定了核苷和核苷酸的结构，获 1957 年诺贝尔化学奖。

Between 1880 and 1900 Kossel identified the bases in nucleic acids. Levene identified ribose in 1909 and deoxyribose in 1929 and proposed that nucleotides are the units of nucleic acids, though his tetranucleotide hypothesis was wrong. In the 1940s Todd confirmed the structures of nucleosides and nucleotides by synthesis and received the 1957 Nobel Prize in Chemistry.

除构成 DNA 和 RNA 外，核苷酸还有多种功能：ATP 是细胞的能量“货币”；GTP 参与信号传导和蛋白质合成；cAMP 和 cGMP 是第二信使；NAD⁺、FAD 和辅酶 A 都含有核苷酸结构，是重要的辅酶。许多抗病毒药物（如阿昔洛韦、瑞德西韦）和抗癌药（如 5-氟尿嘧啶）是核苷或核苷酸类似物。

Besides building DNA and RNA, nucleotides serve many roles: ATP is the cell's energy currency, GTP takes part in signalling and protein synthesis, cAMP and cGMP are second messengers, and NAD⁺, FAD and coenzyme A all contain nucleotide units. Many antivirals (acyclovir, remdesivir) and anticancer drugs (5-fluorouracil) are nucleoside or nucleotide analogues.