twisted around each other in a double helix shape.

形成的雙股螺旋分子

Each strand is made up a sequence of four chemical bases

每一股是由四個化學鹼基形成的序列構成的

represented by the letters A, C, G and T.

分別由字母A,C,G跟T表示

The two strands are complimentary.

DNA兩股是互補的

This means that wherever there's a T in one strand

意思是只要在其中一股上有一個T鹼基

there will be in an A in the opposite strand,

另一股上就會有一個A鹼基與其配對

and wherever there's a C

或者任一地方有C鹼基

there will be a G in the other strand.

另一股上就會有G鹼基與其配對

Each strand has a 5' end and a 3' end.

每一股可分為5'端與3'端

The two strands run in opposite directions.

兩股的方向相反

This determines how each strand of DNA is replicated.

這決定了兩股DNA會如何被複製

The first step in DNA replication is to separate the two strands.

DNA複製的第一步是將兩股分開

This unzipping is done by an enzyme called helicase

這個分開兩股的任務是由叫做解旋酶的酵素負責

and results in the formation of a replication fork.

並且造成複製叉的形成

The separated strands each provide a template for creating a new strand of DNA.

被分開的兩股各自提供了製造新股DNA的模板

An enzyme called primase starts the process.

名為引子酶的酵素開始了複製的過程

This enzyme makes a small piece of RNA

這個酵素製造了小片段的RNA

called a primer.

稱作引子

This marks the starting point for the construction of the new strand of DNA.

引子標記了新股DNA在何處開始被製造

An enzyme called DNA polymerase binds to the primer

名為DNA聚合酶的酵素接上引子

and will make the new strand of DNA.

並且製造DNA的新股

DNA polymerase can only add DNA bases in one direction,

DNA聚合酶只能往一個方向加上DNA的鹼基

from the 5' end to the 3' end.

即從5'端至3'端

One of the new strands of DNA, the leading strand,

其中一股新股DNA，稱作領先股

is made continuously,

能被不間斷的製造

the DNA polymerase adding bases one by one in the 5' to 3' direction.

DNA聚合酶由5'至3'一個接一個的添加新的鹼基

The other strand, the lagging strand, cannot be made in this continuous way

另外一股，稱作延遲股，無法如領先股一樣不間段的製造

because it runs in the opposite direction

因為它的方向與領先股相反

the DNA polymerase can therefore only make this strand in a series of small chunks

因此DNA聚合酶只能夠將延遲股的DNA做成一連串的短片段

called Okazaki fragments.

稱作岡崎片段

Each fragment is started with an RNA primer.

每一個片段由RNA引子起頭

DNA polymerase then adds a short row of DNA bases

接著是被DNA聚合酶由5'端至3'端加上得

in the 5' to 3' direction.

短片段的DNA鹼基

The next primer is then added further down the lagging strand.

下一個引子接著在遠處被接上延遲股

Another Okazaki fragment is then made and the process is repeated again.

接著另一段岡崎片段會被製造，並且一再重複這個過程

Once the new DNA has been made

一旦新的DNA完成製作

the enzyme exonuclease removes all the RNA primers from both strands of DNA.

會由核酸外切酶移除兩股DNA上的RNA引子

Another DNA polymerase enzyme then fills in the gaps that are left behind

另一個DNA聚合酶接著將留下來的空隙

with DNA.

補上DNA

Finally the enzyme DNA ligase seals up the fragments of DNA

最後由DNA連接酶串聯起

in both strands to form a continuous double strand.

在兩股中所有的片段並且形成連續的兩股

DNA replication is described as semi- conservative

DNA複製被形容成半保留複製

because each DNA molecule is made up of one old, conserved strand of DNA

是因為每個雙股DNA分子是由一股舊股，即被保留的DNA舊股

and one new one.

與新股所組成