DNA复制是指原始DNA分子解链并通过碱基互补配对原则形成两个子DNA链的生物学过程，该过程发生在细胞分裂周期的S期。DNA复制以亲代DNA分子为模板，脱氧核苷三磷酸为底物，还需相关酶和蛋白因子的参与，如：DNA聚合酶、DNA引物酶、DNA连接酶、核酸外切酶、拓扑异构酶、引发体等。

DNA复制过程包括引发、延伸、终止三个阶段，DNA双链在复制起点的解旋酶作用下形成单链模板，从RNA引物的3’-OH末端开始，沿5’→3’方向连续不断地添加碱基，再通过共价连接成一条连续完整的新DNA链。

DNA复制具有半保留复制、双向复制、半不连续复制等特点，1953年James Watson和Francis Crick提出DNA双螺旋结构后，1958年Meselson-Stahl实验通过氮同位素标记证实了DNA的半保留复制机制。

DNA复制是生命体最基础的生物学过程，控制着遗传信息的精确和稳定传递，是生物遗传的基础，为生命的演化提供了根基。通过对DNA复制的机制的研究，可以深入了解DNA复制在疾病发生发展中的作用，从而为疾病的诊断、治疗和预防提供依据。例如，DNA复制错误可能引发突变，导致遗传性疾病的发生，如21-三体综合征、先天性的耳聋、色盲、血友病、白化病等。

Let's take a look at DNA replication the process in which DNA copies itself.
让我们来看一下DNA复制,DNA自我复制的过程·
Why does DNA need to copy itself
为什么DNA需要复制自己?
Well before a cell divides during mitosis it must make a copy of its original DNA.
嗯,在有丝分裂期间,细胞在分裂之前必须复制其原始DNA·
This ensures that both resulting daughter cells will have DNA that is identical to the original cell's DNA.
这确保了两个子细胞将拥有与原始细胞DNA完全相同的DNA·
So at what point in the cell cycle does DNA replication happen
那么,DNA复制发生在细胞周期的哪个阶段?
DNA is copied or replicated during the S phase of the cell cycle.
DNA在细胞周期的S期复制或复制·
A good way to remember this is that S stands for synthesis which means to make.
记住这一点的好方法是,S代表合成(synthesis),意思是"制造"·
Now let's see how DNA replicates during the S phase.
现在,让我们看看DNA在S期是如何复制的·
If we zoom into the nucleus we can see the DNA molecules two strands or sides twisted together in the classic double helix formation.
如果我们放大到细胞核内,我们可以看到DNA分子呈经典的双螺旋结构,两个链或两边相互缠绕·
The two strands are connected by hydrogen bonds between their nitrogenous bases.
这两条链通过它们的氮碱基之间的氢键连接在一起·
The first step of replication begins with an enzyme called DNA helicase.
复制的第一步是由一种叫做DNA解旋酶(DNA helicase)的酶开始的·
The suffix A S E or ASE tells you right away that helicase is an enzyme.
后缀A-S-E或ASE表明解旋酶是一种酶·
Helicase unwinds and then separates the two sides of the DNA molecule by breaking the hydrogen bonds between their nitrogenous bases.
解旋酶通过打破氮碱基之间的氢键,解开并分开DNA分子的两条链·
Each separate half of the DNA can now serve as a template or pattern for the creation of a new strand of DNA.
DNA的每一半现在都可以作为模板或图案,用于创建新的DNA链·
This separation exposes all of the nitrogenous bases on both sides of the DNA to the environment within the nucleus where free nucleotides are present.
这种分离使DNA两侧的所有氮碱基暴露在细胞核内的环境中,在那里自由核苷酸存在·
This brings us to the second step in DNA replication the creation of two new identical DNA strands.
这就引出了DNA复制的第二步,即创建两个新的相同的DNA链·
An enzyme that assists in this process is called DNA polymerase.
在这个过程中起作用的酶叫做DNA聚合酶(DNA polymerase)·
It adds free nucleotides available in the nucleus to the original template strands.
它将细胞核中可用的自由核苷酸添加到原始模板链上·
DNA polymerase does this by creating new hydrogen bonds between the available nitrogenous bases of the free nucleotides and those on both sides of the original DNA molecule.
DNA聚合酶通过在自由核苷酸的氮碱基和原始DNA分子两侧的氮碱基之间形成新的氢键来完成这个过程·
New nucleotides are added to the template strands following the base pair rule of nitrogenous bases.
新的核苷酸被添加到模板链上,遵循氮碱基的配对规则·
Remember in DNA adenine always bonds with thymine.
记住,在DNA中,腺嘌呤(A)总是与胸腺嘧啶(T)配对·
Thymine always bonds with adenine.
胸腺嘧啶(T)总是与腺嘌呤(A)配对·
Guanine always bonds with cytosine
鸟嘌呤(G)总是与胞嘧啶(C)配对,
and cytosine always bonds with guanine.
而胞嘧啶(C)总是与鸟嘌呤(G)配对·
So these newly attached nucleotides form a mirror image or complementary strand on each template strand of the original DNA.
因此,这些新附着的核苷酸在原始DNA的每个模板链上形成了镜像或互补链·
As a result of this replication process two duplicate molecules of DNA are produced from the original DNA molecule.
由于这个复制过程,两个DNA的副本分子从原始DNA分子中产生·
With DNA replication now completed the cell is ready to begin mitosis.
DNA复制现在已经完成,细胞准备开始有丝分裂·
We will cover mitosis in another video.
我们将在另一段视频中讲解有丝分裂·
In summary DNA replication is a process in which DNA duplicates itself making an identical copy.
总之,DNA复制是DNA自我复制的过程,生成一个相同的副本·
Replication occurs during the S phase of the cell cycle when a somatic cell is preparing to divide.
复制发生在细胞周期的S期,当一个体细胞准备分裂时·
DNA replication is necessary so that the two daughter cells produced after mitosis both have DNA that is identical to each other and identical to the DNA in the original cell.
DNA复制是必要的,这样在有丝分裂后生成的两个子细胞才能拥有相同的DNA,并且与原始细胞的DNA完全相同·
At the beginning of replication an enzyme called DNA helicase breaks the hydrogen bonds between nitrogenous bases and unwinds the DNA molecule.
在复制的开始,一种叫做DNA解旋酶的酶会打破氮碱基之间的氢键,并解开DNA分子·
Each side of the original DNA molecule serves as a template for the creation of a new complementary strand of DNA.
原始DNA分子的每一侧作为模板,用于创建新的互补DNA链·
With the assistance of DNA polymerase and other enzymes
在DNA聚合酶和其他酶的帮助下,
free nucleotides are added to the template strands following the base pair rule.
遵循氮碱基配对规则,将自由核苷酸添加到模板链上·
The result of DNA replication is two identical duplicate DNA molecules from the original DNA molecule.
DNA复制的结果是从原始DNA分子中生成两个相同的DNA副本·
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