DNA复制(DNA Replication)英文版
大学分子生物学经典双语课件C3： DNA replication
3.1 The principle of DNA replication 3.2 DNA replication model 3.3 Enzymes and protein needed in DNA replication 3.4 Process of DNA replication 3.5 Telomere and Telomerase
parental duplex is unwound.
On the lagging strand, a stretch of single-stranded
parental DNA must be exposed, and then a
segment is synthesized in the reverse direction (relative to fork movement). A series of these fragments are synthesized, then they are joined together to create an intact lagging strand.
v33enzymesandproteinsneededindnareplicationdna聚合酶dna聚合酶dna聚合酶结构基因polapolbpolc亚基1410相对分子质量1030008800083000053聚合酶活性是是是35外切酶活性校正是是是53外切酶活性是否否聚合速度ntss1620402501000持续合成能力32001500500000功能切除引物修复修复复制表31大肠杆菌dna聚合酶的比较?53exonucleaseactivity
enters newly synthesized DNA in the form of
复制转录翻译
3´
结构式
半不连续复制 先导链 随后链 冈崎片断 引物 primer
复制叉 replication fork
DNA复制过程
DNA双螺旋的解除：DNA的解旋过程由DNA解旋酶催化解开后，单链DNA 结合蛋白（SSB ）马上结合在分开的单链上，从而保持其伸展状态。随着解链的进行，在DNA 复制叉前就会形成一种张力而导致超螺旋的产生。现在发现这种张力主要是通过DNA拓扑异构酶的作用消除的。
起始：在一种特殊的RNA聚合酶-DNA引物酶的催化下，先合成一段长5—60个核苷酸的RNA引物，提供3'端自由-OH。然后，在DNA聚合酶Ⅲ的作用下进行DNA的合成。
延伸：只有一条DNA链的合成是连续的，而另一条链的合成是不连续的。所以从整个DNA分子水平来看，DNA两条新链的合成方向是相反的，但是都是从5’端向3’方向延伸。现在一般把一直从5’向3’方向延伸的链称作前导链，它是连续合成的。而另一条先沿5’ —3’方向合成一些片段，然后再由连接酶将其连起来成为长链，称为后随链，其合成是不连续的。这种不连续合成是由冈崎等人首先发现的，所以现在将后随链上合成的DNA不连续单链小片段称为冈崎片段。
b、校对作用：氨酰- tRNA合成酶的水解 部位可以水解错误活化的氨基酸。
原核生物多肽链的合成过程
1、肽链合成的起始
原核生物多肽链的合成分为三个阶段：肽链合成的起始、肽链的延伸、肽链合成的终止和释放。
肽链合成的终止及释放
肽链的延长
30S亚基• mRNA IF3- IF1复合物
30S• mRNA • GTP- fMet –tRNA- IF2- IF1复合物
复制子 replicon
单击此处添加小标题
一个复制起始点控制下复制的一段DNA
生物医学概论生化第4章基因信息的传递和表达
5 3
串联重复序列 反向重复序列
3 5
· · · TGTGGATTA-‖-TTATACACA-‖-TTTGGATAA-‖-TTATCCACA
58
66
166
174
201
209
237
245
E. coli复制起始点 oriC
目录
引发体和引物
Dna B、 Dna C Dna A 5 3
引物 酶
进行解链，进行的是单点起始双向复制。
复制中的放射自显影图象
目录
3. 半不连续复制
3
前导链 (leading strand)
5 3
解链方向
后随链 (lagging strand)
5
目录
顺着解链方向生成的子链，复制是连续进行的， 这股链称为前导链(leading strand) 。
另一股链因为复制的方 A C T G G
T C C A T G A C G G T G A C C
C C A C T G G
G G T G A C C
AT GC GC TA AT CG TA GC CG CG AT CG TA GC GC
+
AT GC GC TA AT CG TA GC CG CG AT CG TA GC GC
氢键，使DNA双链解开成为两条单链。
单链DNA结合蛋白(single stranded DNA binding
protein, SSB) ——在复制中维持模板处于单链状
态并保护单链的完整。
目录
复制起始点附近区域的DNA双链解开成为两条单链。
SSB
解链方向 解螺旋酶
目录
DNA拓扑异构酶改变DNA超螺旋状态、理顺DNA链
名词解释总结
名词解释总结第五章 DNA 复制DNA复制（DNA replication）：亲代双链DNA分子在DNA聚合酶的作用下，分别以各单链DNA分子为模板，聚合与自身碱基可以互补配对的游离的dNTP, 合成出两条与亲代DNA分子完全相同的子代DNA 分子的过程。
复制子（Replicon）:又称复制单位或复制元;DNA中含有一定复制起点和复制终点的复制单位; 1.3万～90万不等复制体（Replisome）：复制叉处的许多酶和蛋白组成的复合体，协同动作合成DNA。
The multi protein (30±) structure that assembles at replicating fork to undertake synthesis of DNA 。
DNA的半保留复制（Semi-Conservation Replication）复制过程中各以双螺旋DNA的其中一条链为模板合成其互补链，新生的互补链与母链构成子代DNA分子复制起点（origin）：复制开始处DNA分子的特定位置原核生物（Prokaryote）：单复制起点真核生物（Eukaryote）：多复制起点复制叉（Replication fork）：染色体中参与复制的活性区域，即复制正在发生的位点复制眼（replication eye）：电子显微镜下观察正在复制的DNA，复制的区域形如一只眼睛慢停突变(slow-stop mutation）在37℃下可以正常发动DNA的复制，当转入42℃的培养条件下，由于DNA的延伸由延长基因控制，整个复制过程不会立即停止，只有当完成这一周期的复制后，下一周期的复制启动不能发动快停突变(fast-stop mutation）复制延长基因温度敏感型突变体，在37℃和42℃下均可以正常发动DNA的复制，但当转入42℃的培养条件下，由于DNA延长基因的突变，整个复制过程表现立即停止的表型。
θ复制(Theta structure replication)双链环状DNA的复制眼可以形成一种θ结构，形状像希腊字母θ，D环式复制（Displacement form replication）线粒体和叶绿体DNA的复制方式，复制起点先是以一条链为模板起始合成DNA的一段序列；两条链的起点并不在同一个点上，由于两条链的起点分开一定距离，所以产生D环复制共价延伸方式（covalence elongation）或滚环式复制（rolling circle replication）多为病毒、细菌因子的复制方式，DNApol三种的比较DNA旋转酶（gyrase）又称拓扑异构酶ⅡDNA解旋酶（DNA helicase）DNA解旋酶是利用ATP水解获得的能量来打断氢键，解开双链DNA并在DNA分子上沿一定方向移动的一类酶的总称（又称解链酶）。
DNA的复制
A gene participates in three major activities:
1. Information Storing 2. Replication 3. Accumulating mutations
Information Storing
Accumulating mutations
三、DNA聚合酶与DNA聚合反应
DNA的复制是由DNA聚合酶（DNA polymerase） 负责完成的，它具有按照模板的指令在模板链 上催化新DNA链合成的活性。 DNA聚合酶是一种模板指导的聚合酶，产物 DNA与模板的碱基组成相同。说明在DNA聚合 酶的作用下，DNA的两条链都能复制。
在适量DNA和镁 离子存在下， DNA聚合酶催化4 种脱氧核糖核苷酸 合成DNA，每次 在DNA的3’-OH末 端加入一个核苷酸 使DNA链由5’向3’ 方向延长，同时释 放无机焦磷酸。
பைடு நூலகம்
半保留复制是双链DNA普遍采用的复制 机制。即使是单链DNA分子，在其复制 过程中也要先形成双链的复制形式。半 保留复制机制说明了DNA在代谢上的稳 定性。
半保留复制作为一个复杂的过程，需要 多种细胞组分的参与。同时为保持遗传 的稳定性，要有高度的忠实性。
二、DNA复制的起点、方向和方式 DNA复制的起点
2）β 二聚体
体外互补实验是鉴定复制体系组分的重 要手段。
二、DNA聚合酶 1 大肠杆菌的DNA聚合酶
大肠杆菌中发现了三种DNA聚合酶：DNA聚 合酶Ⅰ、DNA聚合酶Ⅱ、DNA聚合酶Ⅲ。 DNA聚合酶Ⅰ参与损伤DNA的修复，并在半 保留复制中起切除RNA引物的作用。 DNA聚合酶Ⅱ也参与修复。 DNA聚合酶Ⅲ是一个多亚基的蛋白质，是合 成DNA新链的主要复制酶。
DNA复制
A model for E. coli initiation of DNA replication. The major events in the E. coli initiation of replication are illustrated, (a) Multiple DnaA-ATP proteins bind to the repeated 9-mer sequences within oriC. (b) Binding of DnaA-ATP to these sequences leads to strand separation within the 13-mer repeats. This is mediated by an ssDNA binding domain in DnaA-ATP. (c) DNA helicase (DnaB) and the DNA helicase loader (DnaC) associate with the DnaA bound origin. An ssDNA binding domain in the helicase loader as well as protein interactions with DnaA are required to form this complex.
大肠杆菌DNA聚合酶的种类及其功能
DNA Polymerase I
DNA聚合酶 I (coded by polA)不是大肠杆菌 DNA复制的主 要聚合酶。它具有 3’ →5’ 核酸外切酶活性，保证了 DNA复制 的准确性。它的 5’→3’ 核酸外切酶活性可除去冈崎片段 5' 端 RNA引物，保证连接酶将片段连接起来。
RNA？
机体选择RNA作为引物，其原因可能在于减少致死突变 （ethal mutation）。DNA复制中，从模板拷贝最初的 几个核苷酸时，由于碱基堆集力很弱，其氢键结合能力也
DNA复制转录和翻译-幻灯片(1)
核酸外切酶活性
?
5’ A G C T T C A G G A T A
3’
||||||| ||| |
3’ T C G A A G T C C T A G C G A C 5’
3 5 外切酶活性
辨认错配的碱基对，将其水解－校对
5 3 外切酶活性
切除引物或突变的DNA片段
真核生物的DNA聚合酶
DNA - pol 后随链合成 DNA - pol DNA修复
35 ’’
dCTP
DNA-pol DNA-poDl NA-pDolNA-pol
5
’
dGTP
dTTP
dATP
dATP dGTP
dCTP dTTP
（二）复制的 半不连续性
5
3
解链方向 ’
3
3
5 ’
5
领头链 ( leading strand )
顺着解链方向生成的子链，其复制是连续 进行的，所得到一条连续片段的子链。
引发体（primosome）
引物酶与其他和复制有关的蛋白质形成的复合 物。
DNA连接酶 ( DNA ligase )
连接DNA链 3- OH末端和相邻DNA链5- P 末端，使二者生成磷酸酯键 ，从而把两段相 邻的DNA链连接成完整的链。
ATP
OH P
DNA连接酶在DNA修复、重组、剪接中也起 连接缺口的作用。
功能：
复制终止时，染色体线性DNA末端确有 可能缩短，但通过端粒酶的作用，可以补 偿这种由除去引物引起的末端缩短。
telomerase
端粒酶与药物
hTR和hTERT 核酶 逆转录酶抑制剂 3-叠氮胸苷（AZT）
四、其他复制方式
分子生物学第三章-dna的复制-the replication of dna-2019
4. The Replication Fork（复制叉） 5. DNA Synthesis at the Replication Fork（复制叉上的
DNA合成） 6. Initiation of DNA Replication（复制的起始） 7. Binding and Unwinding（结合和解旋） 8. Finishing Replication（复制的终止）
Fingers （手指）
Thumb（拇指）
Palm （手掌）
DNA聚合酶的3个结构域：拇指，手指，手掌
DNA Polymerase-palm domain(手掌域）
1. Contains two catalytic sites, one for addition of dNTPs and one for removal of the mispaired dNTP.
3. 3. Exonuclease site/proof reading site（校对功能，外切 核酸酶活性位点）
DNA Polymerase-finger domain（手指域）
Binds to the incoming dNTP, encloses the correct paired dNTP to the position for catalysis（手指域中 的几个残基可以和引入的dNTP结合，一旦形成正确的 碱基配对后，手指域即发生移动，包围住dNTP）
Processivity（延伸能力） is a characteristic of enzymes that operate on polymeric substrates（酶 处理多聚体底物的一种特性）
核酸复制(双语)
Conservative replication would leave intact the original DNA molecule and generate a completely new molecule. Dispersive replication would produce two DNA molecules with sections of both old and new DNA interspersed along each strand.
复制的酶学 (Enzymology of DNA Replication)
参与DNA复制的物质
底物(substrate): dATP, dGTP, dCTP, dTTP
聚合酶(polymerase): 依赖DNA的DNA聚合酶，简写
为 DNA-pol
模板(template) : 解开成单链的DNA母链
DNA的生物合成 (Biosynthesis of DNA)
DNA
RNA
protein
DNA Replication
Reverse Transcription
A double stranded nucleic acid is duplicated to give identical copies. This process perpetuates the genetic information and keeps the daughter cells having almost the same genetic information as their parent cell.
The cell cycle is an ordered set of events, culminating in cell growth and division into two daughter cells. The stages are G1-S-G2-M. The G1 stage stands for "GAP 1". The S stage stands for "Synthesis". This is the stage when DNA replication occurs. The G2 stage stands for "GAP 2". The M stage stands for "mitosis", and is when nuclear and cytoplasmic division occur.
E DNA的复制
DNA的复制（DNA Replication）E1 DNA复制概况( Surveys of Replication )DNA复制亲代双链DNA分子在DNA聚合酶的作用下，分别以各单链DNA分子为模板，聚合与自身碱基可以互补配对的游离的dNTP,合成出两条与亲代DNA分子完全相同的子代DNA分子的过程。
1.半保留机制2.复制子、复制起点和复制终点3.半不连续复制4.RNA引导三种可能的DNA复制方式定义：由亲代DNA 生成子代DNA 时，每个新形成的子代DNA 中，一条链来自亲代DNA ，而另一条链则是新合成的，这种复制方式称半保留复制。
一半保留复制中国科学院上海生化与细胞所2002年招收硕士研究生分子遗传学入学考试：请设计一个实验来证明DNA 复制是以半保留方式进行的（8分）。
现已为大家所公认，成为原核生物和真核生物DNA 复制的普遍规律。
15N 标记实验· 细胞生长在15N 标记培养基中· 转入正常N 源培养基中· 分离各代DNA· 分析各代DNA 的浮力密度15N 标记DNACsCL 密度梯度离心浮力密度N15－DNA 1.742g/ml N15－N14－DNA 1.717g/ml N14－DNA 1.710g/ml1958Meselson-stahl设计的CsCl超离心试验证实了DNA复制的这一特性Semiconservative DNA replication Replication fork 亲代链分开及新生链开始复制处称为复制叉模板以3’－5’方向被读，新生链以5’－3’方向合成合成底物为dNTP ，合成能量来自dNTP 水解，并产生焦磷酸DNA半保留复制的生物学意义：DNA的半保留复制表明DNA在代谢上的稳定性，保证亲代的遗传信息稳定地传递给后代。
二复制子、复制起点和复制终点DNA的半保留复制是从DNA分子的特定位点开始的，即复制原点(用ori或o表示)。
DNA 复制(英文版)
C end
• small fragment (323 AA): having 5´→3´ exonuclease activity
• large fragment (604 AA): called Klenow fragment, having DNA polymerization and 3´→5´exonuclease activity
• Transferring the genetic information to the descendant generation with a high fidelity
replication
parental DNA
daughter DNA
Daughter strand synthesis
• Chemical formulation:
Phosphodiester bond formation
DNA replication system
Template: double stranded DNA
Substrate: dNTP
Primer:
short RNA fragment with a
free 3´-OH end
Enzyme:
Replication fork
5' 3'
3'
5'
5'
3'
5'
direction of
3'
replication
Bidirectional replication
• Once the dsDNA is opened at the origin, two replication forks are formed spontaneously.
分子生物学 第十三章 DNA复制(DNA replication)
13.2 DNA polymerases are the enzymes that
make DNA
DNA polymerases are enzymes that synthesize a daughter strand(s) of DNA (under direction from a DNA template). May be involved in repair or replication. DNA replicase is a DNA-synthesizing enzyme required specifically for replication. Repair of damaged DNA can take place by repair synthesis, when a strand that has been damaged is excised and replaced by the synthesis of a new stretch. It can also take place by recombination reactions, when the duplex region containing the damaged is replaced by an undamaged region from another copy of the genome. Replication of duplex DNA takes place by synthesis of two new strands that are complementary to the parental strands. The parental duplex is replaced by two identical daughter duplexes, each of which has one parental strand and one newly synthesized strand. It is called semiconservative because the conserved units are the single strands of the parental duplex.
Chapter 5 DNA复制
DNA聚合酶(DNA polymerase)
DNA聚合酶的共同特点是：
（1）需要提供合成模板； （2）不能起始新的DNA链，必须要有引
物提供3'－OH； （3）合成的方向都是5‘→3’ （4）除聚合DNA外还有其它功能。
大肠杆菌的三合酶种聚合酶
activity, the product of the dnaG gene. The enzyme is a
single polypeptide of 60 kD (much smaller than RNA polymerase).
The primase is an RNA polymerase that is used only under specific circumstances, that is, to synthesize short stretches of RNA that are used as primers for DNA synthesis. DnaG primase associates transiently with the replication complex, and typically synthesizes an 11-12 base primer.
合成，另一个用于后随链的合成。一个复合体 中具有两个聚合酶可以保证两条链以同样的速 度进行合成。
一旦后随链的引物被DNA pol Ⅲ 延伸，会由DNA
polⅠ来将引物去除，并填补上DNA。 DNA polⅠ具有 5‘－3’聚合酶，5‘-3’外切核酸酶以及3‘-5’校正外切核酸 酶活性。
5‘-3’外切核酸酶在去掉引物的同时，聚合酶通过延伸 邻近冈崎片段3‘DNA来填补缺口。两个片段最后的磷酸 二酯键是由DNA连接酶来催化完成的。
DNA replication
Student’s presentation (next week)Paper 2: Wang S, Wang JW, Yu N, Li CH, Luo B, Gou JY, Wang LJ, Chen XY. Control of plant trichome development by a cotton fiber MYB gene. Plant Cell (2004) 16(9): 2323-2334.Group 2 and Group 8DNA replication (recombinationand transposition)Features of DNA replication（DNA复制的特征)1.Semi-conservative (半保留复制)2.Semi-continuous (半连续复制)3.DNA polymerases are template-and primer-dependent(DNA 聚合酶依赖于DNA模板与引物)4.All DNA polymerases synthesize DNA in the 5‘to 3’direction,reading the template 3‘to 5’(所有的DNA聚合酶按5‘-3’方向[模板DNA为3‘-5’方向]合成DNA)5.DNA polymerases require the four deoxynucleosidetriphosphates(dATP, dGTP, dCTP, and dTTP)(DNA聚合酶合成DNA需要4种脱氧核糖核酸分子: dATP, dGTP, dCTP, and dTTP)NextSemiconservative Conservative Dispersive +++Three proposed ways for a double-stranded DNA molecule to be replicated. The red bar represents new synthesized DNA and the green bar represents parental DNA.最初提出的三种可能的DNA复制模式。
DNA Replication
CHAPTER 2 DNA Replication2.1 Semiconservative Replication2.2 Replicon2.3 Replicons of Circle DNA2.4 Prokaryotic DNA Replication2.5 Eukaryotic DNA Replication2.1 Semiconservative Replication•Daughter strand•The antisense strand ofDNA is complementary tothe sense strand, and is theone that acts as thetemplate for synthesis ofmRNA.Meselson-Stahl Experiment (1958)15N14NThe parental duplex is replicated to form two daughter duplexes, each of which consists of one parental strand and one (newly synthesized) daughter strand.This behavior is called semiconservative replication.2.2 RepliconThe replicon(复制子）is a unit of thegenome in which anindividual act of DNAreplication occurs.Each replicon containsan origin for initiationof replication.The replicated regionappears as areplication eye2.2.1 Direction of replicationA bacterium usually has a circular chromosome that isreplicated from a single origin, but a eukaryotic chromosome has many origins, each defining a separate replicon.2.2.2 Replicon organization differs inprokaryotes and eukaryotes2.3 Replicons of Circle DNAD-loop replication（D环复制）Rolling circle replication滚环状复制(σ复制)θReplication(θ复制)2.3.1D-loop replication2.3.2 Replication by rolling circles滚环状复制(rolling circle)φX174replication2.3.3 θstructure•θ复制:是一种双向复制的方式，是许多细菌基因组的复制方式。
Chapter3 DNA复制
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Main function of pol I: excise RNA primer or damaged DNA and fill the gap,
3’→5’ exonuclease activity 3’→5’核酸外切酶活性 5’→3’ exonuclease activity 5’→3’核酸外切酶活性
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DNA 聚合酶催化的反应
T CA 5’ OH
C
+
ppp
OH
T CA C
5’
OH 3’
+
ppi
5 ´ → 3 ´ 聚合作用
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（二）复制的起点、方向和速度 1. Origin of Replication 复制起点 2. Replication/Replicating fork 复制叉 3. Replicon 复制子 4. Direction of replication 复制的方向
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1. 复制起点：
（二） Single-Stranded DNA-Binding Proteins，SSBs （单链DNA结合蛋白） Role of SSB SSB蛋白的作用：
1. 主要起稳定作用，防止单链DNA重新退火形成双螺旋 2. 防止单链DNA 降解 3. 对它们的同源DNA聚合酶具有激活作用
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（一）Semiconservative replication DNA的半保留复制
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（一）Semiconservative replication DNA的半保留复制 1. 定义 DNA复制必须以一条母链为模板以碱基 互补的原则合成新的DNA链，即新合成 的DNA双螺旋由一条母链和一条新合成 的子链构成。
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Elongation of DNA Replication
After RNA primer is synthetized later, the elongation of DNA
begins. The leading chain is continuously synthetized, and the lagging chain is discontinuously synthetized.In the replication fork, DNA helicase moves from 5' to 3' on the DNA template . DNA primase periodically bonds with helicase, and synthetizes new primer in the lagging chain template . Afteran Okazaki fragment is completely synthetized,the core which is responsible for the Okazaki fragment, slides from the sliding clamp and DNA.
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Materials
●Template:One of the strand of dsDNA;
● dNTPs:4 kinbs of deoxynucleotide triphosphates, that's,ATP,GTP,CTP,TTP;
● Primer:usually RNA; ● Proteins and enzyme:such as DNA polymerase,DNA helicase,Singlestrand DNA binding protein （SSB）,DNA topoisomerase,DNA ligase,Telomerase (special in euka-ryotes);
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DNA helicase
In discontinuous reproduction of DNA, it integrats in front of replication fork, catalyzing double chains of DNA to unlink. And it has the activity of ATPase, so two kinds of activivity coupling, by using the activity of ATPase as the energy to unlink two chains.
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Initiation of DNA Replication
Elongation of DNA Replication Finishing of DNA Replication
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The Concepts of DNA Replication
●DNA replication is a process in which two same copies can be obtained.
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Special Constructure of DNA During Replication
Replicon
As a unit for replication a DNA sequence.It contains a replicationorigin, some times it also contains a finishing sequence.
Protokaryotic replicon
Eukaryotic replicon
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Special Constructure of DNA During Replication Replication Fork
It's the Y shape area formed by dsDNA which is being replicated.Unwinded two single templateDNA and the new chains which is being synthetized consist ofthe head of Y , and dsDNA template constitutes the tail of Y.
Replicator
Distinction between the replicator and origin of replication
ቤተ መጻሕፍቲ ባይዱ
-------Origin of replication is always a part of the
replicator.
The specific sites at which DNA unwinding and
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Special Constructure of DNA During Replication
The entire set of cis-acting DNA sequences that is
sufficient to direct the initiation of DNA replication
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Special Constructure of DNA During Replication
Okazaki fragment In DNA discontinuous reproduction, it's the DNA fragments synthetized using the lagging strand template.Then they are covalent connected to a ssDNA. Its length is different in prokaryote and eukaryote.
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SSB
It In te grats w i th ssDNA unlinked by DNA helicase in replication fork,to prevent ssDNA rematching and to protect it from degradating by protein or nucleic acid enzymes.
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Elongation of DNA Replication
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Elongation of DNA Replication
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Enzyme and Protein Involved in Replication ●DNA polymerase; ●DNA helicase; ●Singlestrand DNA binding protein （SSB）; ●DNA topoisomerase; ●DNA ligase; ●Initiator;
• Wuhan University • The College of Life Science
静思笃行 持中秉正
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Contents
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The Concepts of DNA Replication Materials And Special Constructure of DNA Enzyme and Protein Involved in Replication
and continues to synthetze leading chain
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Initiation of DNA Replication
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Elongation of DNA Replication
The Constructure of Elongation DNA Replication
origin
initiation of replication occur,are required for DNAreplication initiation. It's sequence are rich in AT , usually is a cross structure
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DNA Ligase Nicks occur in the deve-loping molecule becau-se the RNA primer is removed and synthesis proceeds in a discontinuous manner on the lagging strand. The final replicationproduct does not have any nicks bec-ause DNA ligase forms a covalent phosphodiester bond between 3'hydroxyl and 5'phosphate groups.
●In E.coli，Dna A bonds 9bp reverse repeat sequences,
and degenerates 13bpsequences.Then open initiation complex is formed.
●In the condition that ATP offer energy,13bpare unlinked.
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Enzyme and Protein Involved in Replication
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DNA polymerase
It is the enzyme using one of strand of dsDNA as a template to synthetize new DNA . It has two domains that's, palm domain, t humb d omain a n d fingers domain. It has three activity, 3'-5' and 5'-3' exonuclease activity;DNA polymerase.