What is DNA replication?

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DNA replication: A wondrous complex process whereby the ("parent") strands of DNA in the double helix are separated and each one is copied to produce a new ("daughter") strand. This process is said to be "semi-conservative" since one of each parent strand is conserved and remains intact after replication has taken place.

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The copying of the double-stranded DNA molecule, producing two identical DNA double helices.


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One of the most important features of DNA is the ability to have many copies made of it. The process of making copies of DNA molecules within the cell nucleus is called DNA replication. The Watson-Crick double helix model for DNA allows for a simple way that exact copies of the DNA molecule can be produced. This simple method is referred to as semi-conservative replication.

Each DNA molecule is made up of two strands of DNA that are bound together by hydrogen bonds. The hydrogen bonds form between complementary base pairs, or nucleotides. Adenine always pairs with thymine and cytosine always pairs with guanine. When a DNA molecule is split into two separate strands, free nucleotides in the nucleus can bond with the unpaired bases of each strand. This is exactly what happens during DNA replication.

During the replication process, the two strands of DNA that make up the double helix are split. Free nucleotides in the nucleus pair with the matching bases of the two single strands. The nucleotides are joined together forming a new complementary strand of DNA. The two resulting copies of the DNA molecule have one new strand and one from the original molecule. This is why DNA replication is called semi-conservative – half of each molecule is new and half is conserved from the DNA molecule being copied.


There are many enzymes that are involved in the DNA replication process and each manages a specific step. The DNA double helix structure is very stable and DNA is often found in a highly coiled state, so the two strands will not split without some help. DNA gyrases work to relax, or uncoil, the DNA molecule. As the DNA is uncoiled, another enzyme begins to unzip the DNA molecule or break the hydrogen bonds between the base pairs. Single-strand binding proteins then bind to the separated strands in order to keep them apart and allow replication to occur.

Keeping the strands apart allows the free-floating nucleotides to form hydrogen bonds with their complementary pair. Once the nucleotides are in position, DNA polymerase joins the free nucleotides together, forming the backbone of the DNA strand. Lastly, DNA ligase runs along the new backbones and fills any gaps that occurred during the replication process.

Exact replication of DNA is important as DNA carries the genetic information for the cell. If genetic information is to be passed from each generation to the next, there must be some way of duplicating the information. This is the ultimate role of DNA replication – to produce exact copies of the genetic material that can be passed on to the next generation of cells.

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