第14章核苷酸的代谢-2014

1、第十四章核苷酸的代谢第十四章核苷酸的代谢众所周知，早睡早起不仅有利于身体健康，同时也有益于大脑的思维活跃度。然而，西班牙的一项研究结果却推翻了这个“既定”理论，认为晚睡晚起的“夜猫子”较早睡早起人群更加聪明、健康，同时收入也相对更高。英国每日邮报3月24日报道，西班牙马德里大学的研究人员对近1000名青少年的习惯和生物钟进行研究，发现大多数晚睡晚起的人比早起的人更聪明，同时也更健康。研究结果显示，那些常常熬夜的人通常拥有声望较高的工作和较高的收入，这些人的智力往往也更高。研究称，晚睡者归纳推理、抽象分析及解决问题的能力优于早睡者，这些与创造力有关，他们更可能取得较大成就。而那些早睡者一般考试成

2、绩很好，这也许是因为晚睡者在白天表现得不好。拉夫堡大学的心理学家霍恩(Jim Horne)说：“晚睡者偏外向和创造性，如诗人、艺术家和发明家，而早睡者推理能力较强，如会计和公务员等。”研究表明“夜猫子”更聪明健康 收入也更高？2013-03-25 18:38:17著名的夜猫子：温斯顿丘吉尔（左）与查尔斯达尔文（右）妈妈叫我了？絶滅救！皮膚絶滅救！皮膚細胞細胞読売新聞 3月25日(日)11時34分配信絶滅危機体細胞、種類細胞変化細胞（新型万能細胞）作製、豪大学研究成功。将来、細胞卵子精子変化、繁殖保護役立可能性。、大型科動物。中央山間部頭程度生息、近年、減少傾向。研究、成体皮膚細胞採取。山中伸弥

3、京都大教授開発種類遺伝子使一般的方法細胞作製、遺伝子加種類使成功。細胞生殖細胞変研究、京都大学精子作製成功。大、科動物細胞作製世界初、今後、科絶滅危惧動物作製目指。 最終更新:3月25日(日)11時34分Snow Leopard Trust(学名学名: Panthera uncia)、中央山岳地帯生息、中央山岳地帯生息、絶滅危惧種絶滅危惧種 科動物。希少動物警戒心強、科動物。希少動物警戒心強、険遠隔地域生息険遠隔地域生息 釈迦様関係深神経伝達物質釈迦様関係深神経伝達物質!?血液中物質調、病。体、心状態血液検査時代。心物質、心血液、目病診断最新動向紹介！例糖尿病血液中血糖値上昇。脂質異常症、中性

4、脂肪増。体知血液。、心。心不調血液教。答！、病、血液検査、驚。病、血液中酸（ ethanolamine phosphate， ， EAP）物質減明。重症程、減方大、逆治療元気、増話、外苑川村則行院長。磷酸乙醇胺川村院長川村院長07年、代謝物解析手掛年、代謝物解析手掛社共同、病指標物質研究社共同、病指標物質研究。538物質調結果、物質調結果、EAP着。着。EAP肝臓肝臓心臓、最多存在脳。喜快感、動機心臓、最多存在脳。喜快感、動機関関 神経伝達物質働後神経伝達物質働後代謝物（川村院長）代謝物（川村院長）、釈迦様、釈迦様弟子弟子“ “” ”由来。語由来。語“ “歓喜歓喜” ”意味。仏教喜脳内物質意味

5、。仏教喜脳内物質。神経伝達物質。神経伝達物質、奥深。、奥深。 血漿血漿中濃度約中濃度約25 M。 。 中文名称中文名称:2-氨乙基磷酸二氢 中文同义词中文同义词: 2-氨基乙醇-1-磷酸;磷酰乙醇胺;乙醇胺磷酸酯;2-氨乙基磷酸二氢;O-磷酸乙醇胺;磷酸乙醇胺 英文名：英文名：O-PHOSPHORYLETHANOLAMINEethanolamine phosphate酸（酸（ethanolamine phosphate）O-酸酸（O-phosphoethanolamine）、広生物界見）、広生物界見天然化合物。天然化合物。-1-酸酸、脂質脂質-1-酸酸酸酸trans-2-生。同様経路、生。同様

6、経路、-1-酸酸生成。、生成。、 、 ATP酸酸ADP生。生。酸、内因性酸、内因性前駆体前駆体酸酸一部一部1。 。血漿血漿中濃度約中濃度約25 M。 。社、社、塩形塩形販販売。効能、売。効能、細胞膜細胞膜強化謳。、最近強化謳。、最近病病患者患者血漿血漿中濃度低下報道中濃度低下報道Key Termsnucleosidenucleotide pyrimidinecarbamoyl phosphate synthetase (CSP)ATP-grasp fold5-phosphoribosyl-1-pyrophosphate (PRPP)orotidylatepurinesalvage pathwa

7、yinosinatehypoxanthineglutamine phosphoribosyl amidotransferaseribonucleotide reductasethymidylate synthasedihydrofolate reductaseIII. Synthesizing RNABase Ribonucleoside Ribonucleotide (5 -monophosphate)Adenine (A) Adenosine Adenylate (AMP)Guanine (G) Guanosine Guanylate (GMP)Uracil (U) Uridine Uri

8、dylate (UMP)Cytosine (C) Cytidine Cytidylate (CMP) DNABase Deoxyribonucleoside Deoxyribonucleotide (5 -monophosphate)Adenine (A) Deoxyadenosine Deoxyadenylate (dAMP)Guanine (G) Deoxyguanosine Deoxyguanylate (dGMP)Thymine (T) Thymidine Thymidylate (TMP)Cytosine (C) Deoxycytidine Deoxycytidylate (dCMP

9、)一核苷酸的化学一核苷酸的化学Purines and Pyrimidines. Atoms within bases are numbered without primes. Uracil instead of thymine isused in RNA.二二 核苷酸的生物合成核苷酸的生物合成 嘌呤核苷酸的生物合成嘌呤核苷酸的生物合成 嘧啶核苷酸的生物合成嘧啶核苷酸的生物合成 脱氧核糖核苷酸的生物合成脱氧核糖核苷酸的生物合成Nucleotides Are the Monomeric Units of Nucleic AcidsNucleotide Mono-, Di-, and Triphos

10、phates Are InterconvertibleHow is the other major pyrimidine ribonucleotide, cytidine, formed? It is synthesized from the uracil base of UMP, but UMP is converted into UTP before the synthesis can take place. Recall that the diphosphates and triphosphates are the active forms of nucleotides in biosy

11、nthesis and energy conversions. Nucleoside monophosphates are converted into nucleoside triphosphates in stages. First, nucleoside monophosphates are converted into diphosphates by specific nucleoside monophosphate kinases that utilize ATP as the phosphoryl-group donor 。For example, UMP is phosphory

12、lated to UDP by UMP kinase. Nucleoside diphosphates and triphosphates are interconverted by nucleosi diphosphate kinase, an enzyme that has broad specificity, in contrast with the monophosphate kinases. X and Y can represent any of several ribonucleosides or even deoxyribonucleosides.P 嘌呤的组成嘌呤的组成一、嘌

13、呤核苷酸的生物合成一、嘌呤核苷酸的生物合成 1从从头头合成途径：合成途径： 示踪原子法示踪原子法证证明，明，嘌嘌呤核苷酸中的呤核苷酸中的嘌嘌呤呤环环是由多种小分子是由多种小分子化合物逐步化合物逐步组组装而成的。装而成的。 a. 嘌嘌呤核苷酸不是先合成呤核苷酸不是先合成嘌嘌呤碱再与戊糖，磷酸呤碱再与戊糖，磷酸结结合，而合，而是由是由5-磷酸核糖磷酸核糖合成合成5-磷酸核糖焦磷酸（磷酸核糖焦磷酸（PRPP） ）开始，先逐开始，先逐步合成步合成为为次黄次黄嘌嘌呤呤（ （IMP），），然后再由然后再由IMP合成腺合成腺嘌嘌呤核苷呤核苷酸酸（ （AMP） ）和和鸟嘌鸟嘌呤核苷酸呤核苷酸（ （GMP） ）

14、。催化。催化这这些反些反应应的的酶酶均存均存在于在于胞液胞液中。中。 b. AMP和和GMP是是嘌嘌呤核苷酸生物合成的反呤核苷酸生物合成的反馈馈抑制抑制剂剂。 。 c. AMP和和GMP可分可分别转变为别转变为相相应应的二磷酸核苷和三磷酸的二磷酸核苷和三磷酸核苷。核苷。 2 补补救途径救途径 腺腺嘌嘌呤核糖磷酸呤核糖磷酸转转移移酶酶和次黄和次黄嘌嘌呤呤鸟嘌鸟嘌呤核糖呤核糖转转移移酶酶催催化下腺化下腺嘌嘌呤和呤和鸟嘌鸟嘌呤（次黄呤（次黄嘌嘌嘌嘌呤）分呤）分别别生成生成AMP和和GMP（ （IMP）。）。（一）嘌呤核苷酸的合成（一）嘌呤核苷酸的合成 磷酸核糖焦磷酸激酶磷酸核糖焦磷酸激酶5-磷酸核糖

15、磷酸核糖 + ATP 5-磷酸核糖磷酸核糖-1-焦磷酸焦磷酸 （ （PRPP） +AMP 谷氨酰胺谷氨酰胺PRPP氨基转移酶（关键酶）氨基转移酶（关键酶） PRPP 5-磷酸核糖磷酸核糖-1 胺胺(PRA) PRPP经经10步反应生成步反应生成IMPIMP生成生成AMP和和GMPAMP 和和GMP生成生成ADP，ATP和和GDP，GTP5-磷酸核糖磷酸核糖-1-焦磷酸焦磷酸The Purine Ring System Is Assembled on Ribose PhosphateDe novo purine biosynthesis, like pyrimidine biosynthesis

16、, requires PRPP, but for purines, PRPP provides the foundationon which the bases are constructed step by step. The initial committed step is the displacement of pyrophosphate by ammonia, rather than by a preassembled base, to produce 5-phosphoribosyl-1-amine, with the amine in the bconfiguration.5-磷

17、酸核糖磷酸核糖-1 胺胺(PRA)谷氨谷氨酰酰胺胺PRPP氨基氨基转转移移酶酶是关是关键酶键酶（PRA）AMP and GMP Are Formed from IMPde Novo Pathway for Purine Nucleotide Synthesis. The origins of the atoms in the purine ring areindicated.次黄嘌呤次黄嘌呤核苷酸核苷酸黄嘌呤核苷酸黄嘌呤核苷酸磷酸腺苷琥珀酸磷酸腺苷琥珀酸In a salvage pathway, a base is reattached to a ribose, activated in th

18、eform of 5-phosphoribosyl-1-pyrophosphate (PRPP). In de novo synthesis, the base itself is synthesized from simplerstarting materials, including amino acids. ATP hydrolysis is required for de novo synthesis.Inosinate Formation. The removal of fumarate, the addition of a second formyl group from N 10

19、-formyltetrahydrofolate, and cyclization completes the synthesis of inosinate (IMP), a purine nucleotide.III. Synthesizing the Molecules of Life 25. Nucleotide Biosynthesis 25.2. Purine Bases Can Be Synthesized de Novo or Recycled by Salvage PathwaysGenerating AMP and GMP. Inosinate is the precursor

20、 of AMP and GMP. AMP is formed by the additionof aspartate followed by the release of fumarate. GMP is generated by the addition of water, dehydrogenation by Nand the replacement of the carbonyl oxygen atom by -NH2 derived by the hydrolysis of glutamine.de Novo Purine Biosynthesis. 1. Glycine is cou

21、pled to the amino group of phosphoribosylamine. 2. N 10-Formyltetrahydrofolate transfers a formyl group to the amino group of the glycine residue. 3. The inner amide group isphosphorylated and converted into an amidine by the addition of ammonia derived from glutamine. 4. An intramolecularcoupling r

22、eaction forms the five-membered imidazole ring. 5. Bicarbonate adds first to the exocyclic amino group andthen to a carbon atom of the imidazole ring. 6. The imidazole carboxylate is phosphorylated, and the phosphate isdisplaced by the amino group of aspartate.III. Synthesizing the Molecules of Life

23、 25. Nucleotide Biosynthesis 25.2. Purine Bases Can Be Synthesized de Novo or Recycled by Salvage Pathways谷氨酰胺谷氨酰胺PRPP氨基转移酶是关键酶氨基转移酶是关键酶XMP-谷氨酰谷氨酰胺转移酶胺转移酶腺苷酸（基）腺苷酸（基）琥珀酸裂解酶琥珀酸裂解酶磷酸核糖焦磷酸合成酶磷酸核糖焦磷酸合成酶PRPPIMPIMPAGP GMPAnticancer Drug Targets. Thymidylate synthase and dihydrofolate reductase are choice

24、targets in cancerchemotherapy because the generation of large quantities of precursors for DNA synthesis is required for rapidly dividingcancer cells. 补补 救救 途途 径径磷酸核糖转移酶磷酸核糖转移酶 腺嘌呤腺嘌呤+PRPP 腺苷酸腺苷酸+PPi 鸟嘌呤鸟嘌呤+PRPP 鸟腺苷酸鸟腺苷酸+PPi 次黄嘌呤次黄嘌呤+PRPP 次黄腺苷酸次黄腺苷酸+PPi核苷磷酸化酶、核苷磷酸激酶核苷磷酸化酶、核苷磷酸激酶 碱基碱基+1-磷酸核糖磷酸核糖 核苷核苷

25、+Pi 核苷核苷+ATP 核苷酸核苷酸+ATP（二）嘧啶核苷酸的生物合成（二）嘧啶核苷酸的生物合成 氨甲酰磷酸（氨甲酰磷酸（细胞质细胞质中合成）中合成） 乳清酸乳清酸 UMP合成合成 UMP UDP UTP UTP CTP CDP CMPde Novo Pathway for Pyrimidine Nucleotide Synthesis. The C-2 and N-3 atoms in the pyrimidine ringcome from carbamoyl phosphate, whereas the other atoms of the ring come from asparta

26、te.1从从头头合成途径：合成途径：同位素同位素标记实验证标记实验证明，明，嘧啶环嘧啶环是由氨甲是由氨甲酰酰磷酸和天冬氨酸合成磷酸和天冬氨酸合成。 。嘧啶嘧啶核苷酸的合成与核苷酸的合成与嘌嘌呤核苷酸合成不同，它是呤核苷酸合成不同，它是先装配好先装配好嘧啶环嘧啶环，而后再与磷酸核糖基，而后再与磷酸核糖基团结团结合，形成乳清酸核合，形成乳清酸核苷酸。苷酸。再再转化为其他嘧啶核苷酸。转化为其他嘧啶核苷酸。A） ）在在动动物体内合成物体内合成嘧啶时嘧啶时， ，氨甲氨甲酰酰磷酸合成是在胞液磷酸合成是在胞液中（尿素合成中是在中（尿素合成中是在线线粒体内）粒体内）进进行的而且谷氨行的而且谷氨酰酰胺是氨基供体

27、，反胺是氨基供体，反应应消耗消耗2分子分子ATP，由氨甲，由氨甲酰酰合成合成酶酶催化。氨甲催化。氨甲酰酰磷酸磷酸与天冬氨酸反与天冬氨酸反应应生成生成氨甲氨甲酰酰天天门门冬氨酸冬氨酸，然后脱水，然后脱水闭环闭环形成形成二二氢氢乳酸乳酸，随后脱，随后脱氢转变为氢转变为乳清酸乳清酸，再从，再从PRPP中得到磷酸核糖基中得到磷酸核糖基团团生成生成乳清酸核苷酸乳清酸核苷酸，它，它经经脱脱羧羧形成形成UMP。 。B） ）UMP可以生成可以生成UDP和和UTP。 。C） ）UTP经经氨基化生成三磷酸胞苷（氨基化生成三磷酸胞苷（CTP）。）。D） ）CTP可以生成可以生成CDP和和CMP。 。2补救途径补救途

28、径A）在尿苷磷酸化）在尿苷磷酸化酶酶催化下尿催化下尿嘧啶嘧啶和和1-磷酸核糖。生成尿苷，然后尿苷在尿苷激磷酸核糖。生成尿苷，然后尿苷在尿苷激酶酶的作用的作用下生成下生成UMP（ （较为较为重要）重要）B） ）. 在在UMP磷酸核糖磷酸核糖转转移移酶酶催化下，尿催化下，尿嘧啶嘧啶和和5-磷酸核糖焦磷酸生成磷酸核糖焦磷酸生成UMP。 。 嘧啶核苷酸的生物合成嘧啶核苷酸的生物合成氨甲酰磷酸氨甲酰磷酸（细胞质中合成）（细胞质中合成）氨甲酰天冬氨酸氨甲酰天冬氨酸二氢乳清酸二氢乳清酸乳清酸乳清酸乳清酸核苷酸乳清酸核苷酸CTP Is Formed by Amination of UTPAfter uridi

29、ne triphosphate has been formed, it can be transformed into cytidine triphosphate by the replacement of a carbonyl group by an amino group.（三）、脱氧核糖核苷酸的合成脱氧核糖核苷酸主要是由二磷酸核苷还原所生成。哺乳动物中已分离脱氧核糖核苷酸主要是由二磷酸核苷还原所生成。哺乳动物中已分离出出核糖核苷酸还原酶核糖核苷酸还原酶，它包括，它包括二磷酸核苷还原酶二磷酸核苷还原酶，硫氧还蛋白（硫氧还蛋白（具有具有氧化型和还原型）氧化型和还原型）和硫氧还蛋白还原酶和硫氧

30、还蛋白还原酶。A）在二磷酸核苷还原酶催化下，将二磷酸核苷还原为二磷酸脱氧核在二磷酸核苷还原酶催化下，将二磷酸核苷还原为二磷酸脱氧核苷，而苷，而硫氧还蛋白提供两个氢原子后由还原型转变为氧化型硫氧还蛋白提供两个氢原子后由还原型转变为氧化型。氧化型氧化型硫氧还蛋白在硫氧还蛋白还原酶的催化下转变为还原型硫氧还蛋白硫氧还蛋白在硫氧还蛋白还原酶的催化下转变为还原型硫氧还蛋白。此反应的氢是由此反应的氢是由NADPH提供的。提供的。B）二磷酸核苷还原酶特异性不高可催化四种二磷酸核苷（二磷酸核苷还原酶特异性不高可催化四种二磷酸核苷（NDP）转）转变为四种脱氧二磷酸核苷（变为四种脱氧二磷酸核苷（dNDP）。）。

31、C）dNDP可以生成可以生成dNTP和和dNMP。 D）胸苷酸合成胸苷酸合成 尿嘧啶脱氧核苷酸（尿嘧啶脱氧核苷酸（dUMP）甲基化生成）甲基化生成dTMP，dTMP可以生成可以生成dTDP和和dTTP。NDP dNDP硫氧还蛋白硫氧还蛋白谷氧还蛋白谷氧还蛋白氧化型氧化型氧化型氧化型NDP dNDP NDPdNDP dAMPdADPdATP dGMPdGDPdGTP dCMPdCDPdCTP dUMP dUDPdUTP dUMP dTMP dTDP dTTPThymidylate Synthesis. Thymidylate synthase catalyzes the addition of

32、a methyl group (derived from N 5,N 10-methylenetertahydrofolate to dUMP to form TMP. The addition of a thiolate from the enzyme activates dUMP.Opening the five-membered ring of the THF derivative prepares the methylene group for nucleophilic attack by theactivated dUMP. The reaction is completed by

33、the transfer of a hydride ion to form dihydrofolate.Control of Purine Biosynthesis. Feedback inhibition controls both the overall rate of purine biosynthesisand the balance between AMP and GMP production. 补补 救救 途途 径径磷酸核糖转移酶磷酸核糖转移酶 尿嘧啶尿嘧啶+PRPP 尿嘧啶核苷酸尿嘧啶核苷酸+PPi 胞嘧啶胞嘧啶 不能不能 核苷磷酸化酶、核苷磷酸激酶核苷磷酸化酶、核苷磷酸激酶 尿

34、嘧啶尿嘧啶+1-磷酸核糖磷酸核糖 尿嘧啶核苷尿嘧啶核苷+Pi 嘧啶核苷嘧啶核苷+ATP 嘧啶核苷酸嘧啶核苷酸+ATPIn de Novo Synthesis, the Pyrimidine Ring Is Assembled from Bicarbonate, Aspartate,and Glutamine The pyrimidine ring is assembled first and then linked to ribose phosphate to form a pyrimidine nucleotide. PRPP is the donor of the ribose phosp

35、hate moiety. The synthesis of the pyrimidine ring starts with the formation of carbamoylaspartate from carbamoyl phosphate and aspartate, a reaction catalyzed by aspartate transcarbamoylase. Dehydration, cyclization, and oxidation yield orotate, which reacts with PRPP to give orotidylate. Decarboxyl

36、ation of this pyrimidine nucleotide yields UMP. CTP is then formed by the amination of UTP.Purines Bases Can Be Synthesized de Novo or Recycled by Salvage Pathways The purine ring is assembled from a variety of precursors: glutamine, glycine, aspartate, N 10-formyltetrahydrofolate,and CO2. The commi

37、tted step in the de novo synthesis of purine nucleotides is the formation of 5-phosphoribosylamine from 5-phosphoribosyl-1-pyrophosphate (PRPP) and glutamine. The purine ring is assembled on ribose phosphate, in contrast with the de novo synthesis of pyrimidine nucleotides. The addition of glycine,

38、followed by formylation,amination, and ring closure, yields 5-aminoimidazole ribonucleotide. This intermediate contains the completed fivemembered ring of the purine skeleton. The addition of CO2, the nitrogen atom of aspartate, and a formyl group, followedby ring closure, yields inosinate (IMP), a

39、purine ribonucleotide. AMP and GMP are formed from IMP. Purineribonucleotides can also be synthesized by a salvage pathway in which a preformed base reacts directly with PRPP.Deoxyribonucleotides Are Synthesized by the Reduction of Ribonucleotides Through aRadical MechanismDeoxyribonucleotides, the

40、precursors of DNA, are formed in E. coli by the reduction of ribonucleoside diphosphates.These conversions are catalyzed by ribonucleotide reductase. Electrons are transferred from NADPH to sulfhydryl groups at the active sites of this enzyme by thioredoxin or glutaredoxin. A tyrosyl free radical ge

41、nerated by an iron center in the reductase initiates a radical reaction on the sugar, leading to the exchange of H for OH at C-2 . TMP is formed by methylation of dUMP. The donor of a methylene group and a hydride in this reaction is N 5,N 10-methylenetetrahydrofolate, which is converted into dihydr

42、ofolate. Tetrahydrofolate is regenerated by the reduction of dihydrofolate by NADPH. Dihydrofolate reductase, which catalyzes this reaction, is inhibited by folate analogs such as aminopterin and methotrexate. These compounds and fluorouracil, an inhibitor of thymidylate synthase, are used as antica

43、ncer drugs.Key Steps in Nucleotide Biosynthesis Are Regulated by Feedback Inhibition Pyrimidine biosynthesis in E. coli is regulated by the feedback inhibition of aspartate transcarbamoylase, the enzyme that catalyzes the committed step. CTP inhibits and ATP stimulates this enzyme. The feedback inhi

44、bition of glutamine-PRPP amidotransferase by purine nucleotides is important in regulating their biosynthesis. 四，四，核酸的酶促降解 在动物体内有多种水解核酸的酶称为核酸酶。它们分别将在动物体内有多种水解核酸的酶称为核酸酶。它们分别将RNA和和DNA水解为水解为单核苷酸单核苷酸。另外依据其作用于核酸的位置不同可分为。另外依据其作用于核酸的位置不同可分为内切核酸酶（从分子内部切断）和外切核酸酶（由核酸的末端一内切核酸酶（从分子内部切断）和外切核酸酶（由核酸的末端一个一个的切下单核苷酸）

45、。经核酸酶水解产生的单核苷酸受核苷个一个的切下单核苷酸）。经核酸酶水解产生的单核苷酸受核苷酸酶的水解生成核苷和磷酸。核苷在核苷酶的作用下进一步分解。酸酶的水解生成核苷和磷酸。核苷在核苷酶的作用下进一步分解。核苷酶种类很多。核苷酶种类很多。 外切酶外切酶（无特异性，但作用方向有差别）（无特异性，但作用方向有差别） 从核酸分子的一端逐一把核苷酸水解下来，是碱基非特异性磷酸二从核酸分子的一端逐一把核苷酸水解下来，是碱基非特异性磷酸二酯酶酯酶（ ） ）限制性内切酶限制性内切酶 细菌或霉菌中识别并水解细菌或霉菌中识别并水解外源双链外源双链DNADNA的酶的酶, ,可将大分子核酸水解成可将大分子核酸水解成

46、小分子核酸片断。常用的小分子核酸片断。常用的限制性内切酶有识别位点，识别位点一限制性内切酶有识别位点，识别位点一般长般长4-84-8个碱基对。个碱基对。 DNADNA分子切割后形成黏性末端或平齐末端。分子切割后形成黏性末端或平齐末端。 EcoR1（黏性末端黏性末端） 5-GAATTC -3 5-G + AATTC- 3 3-CTTAAG -5 3-CTTAA + G-5 Hae （平齐末端平齐末端） 5-GG CC-3 5 -GG + CC-3 3 -CC GG-5 3 -CC + GG-5 Specificities of Some Restriction Endonucleases. Th

47、e base-pair sequences that are recognized by theseenzymes contain a twofold axis of symmetry. The two strands in these regions are related by a 180-degree rotation aboutthe axis marked by the green symbol. The cleavage sites are denoted by red arrows. The abbreviated name of eachrestriction enzyme is given at the right of the sequence that it recognizes.核酸的水解过程如下： 戊糖戊糖 核酸核酸 低聚核苷酸低聚核苷酸 核苷酸核苷酸 磷酸核苷磷酸核苷 碱基碱基 DNA中的戊糖是中的戊糖是D2脱氧核糖脱氧核糖； RNA中的戊糖是中的戊糖是