How Does DNA Copy Itself?

Contributor: Hannah Brooks. Lesson ID: 12207

Living creatures have been around a lot longer than photocopiers! So, how did DNA replicate, or copy, itself before modern technology? Then, as now, it's by an amazing procedure that keeps us alive!


Life Science

learning style
personality style
Grade Level
Middle School (6-8), High School (9-12)
Lesson Type
Dig Deeper

Lesson Plan - Get It!


What if there were only a single copy of the blueprint for all the houses in a housing development? How would they all be built? What do you think would happen if DNA never replicated?

If DNA never replicated, living things would not be able to live very long, because DNA is the blueprint for life!

It is responsible for telling cells when to divide, how to carry out different functions, and build proteins.

  • So, how does a molecule make a copy of itself?

It carries out a process called, "DNA replication." This process starts in the cell nucleus.

Before continuing, if you missed, or want a refresher in, the previous lesson in this What Is DNA? series, find it under Related Lessons in the right-hand sidebar.

animal cell

The nucleus keeps the DNA safe, and DNA is too large to ever leave the nucleus. DNA replication starts with the two strands "unzipping" from one another. This separation is aided by an enzyme, a special protein, called, "Helicase."


Notice how there is now space between the singular strands. This space allows new nitrogen bases to come and bond, creating a new double strand of DNA.

  • Remember how DNA bases bond?

You learned in the previous lesson that cytosine bonds with guanine, and adenine only bonds with thymine! There is another enzyme responsible for making sure the bonding pattern is correct: DNA polymerase.

DNA replication

  • How many DNA polymerase enzymes do you see in the image?

That's right, there are two working at the same time to ensure that the DNA is copied correctly!

DNA replication is called "semi-conservative" because it creates a new strand from an old strand acting as a template. Imagine tracing a new image by using an old image as a model; this is the same idea as DNA replication.

  • Can you believe that this entire process is occurring in the cell nucleus, which is much smaller than a single cell?

DNA replication is a necessary process to keep cells functioning well and to pass on genetic information.

  • Can you give an overview of DNA replication?
  • It starts with the two strands unzipping, which is helped along by what enzyme?

Then, DNA polymerase helps the DNA match bases to create a new strand. See if you can explain the process to a parent or teacher!

Now, you are ready to move to the Get It? section to work with an online interactive.

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