Okazaki Fragments: Definition & Overview

Lesson Transcript
Instructor: Adrianne Baron

Adrianne has a master's degree in cancer biology and has taught high school and college biology.

Learn what Okazaki fragments are and how they are formed during the process of DNA replication. There is a short quiz to follow to see how well you understand the lesson.

Definition of Okazaki fragments

'What a strange-looking and sounding term,' may be the first thing that popped into your mind when you first heard the words 'Okazaki fragments.' I know that was my first impression. My next thought was that whatever they are, they're probably pretty complicated with a name like that. As I found out, that wasn't really the case! So what exactly does that complicated term refer to?

Okazaki fragments are fragments of DNA that are produced during the process of DNA replication. So now you may be thinking the same thing that I thought next which is, 'why not just call them DNA fragments?' Well, scientists have this knack for liking to name their discoveries after themselves or something that relates to them. Can you guess who discovered the DNA fragments? Yep, you probably guessed. They were discovered by a scientist by the name of Reiji Okazaki.

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Formation of Okazaki Fragments

We've covered some of your initial thoughts on these fragmented pieces of DNA, so let's move on to the next thought. How are these fragments formed, and what is their significance? Okazaki fragments are formed as the lagging strand of DNA is copied. Let's quickly look at how this process happens.

Remember that DNA is structured like a double helix, which looks a lot like a spiral staircase. There are two strands that compose the double helix. The double helix is opened up for the process of replication to take place by DNA helicase. DNA helicase is an enzyme that breaks the hydrogen bonds that hold the DNA in the double helix structure. One strand is opened in the 5' - 3' direction, which is the forward direction, and is called the leading strand. The other strand is opened in the 3' - 5' direction, which is the reverse direction, and is called the lagging strand.

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