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DNA Ligase: Definition & Role

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  • 0:01 DNA Ligase Defined
  • 1:16 Role of DNA Ligase
  • 2:53 Lesson Summary
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Lesson Transcript
Instructor: Adrianne Baron

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

You will learn how everything comes together at the end of DNA replication through the actions of DNA ligase. Once you think you know the lesson, then take the quiz to check your understanding.

DNA Ligase Defined

DNA ligase is an enzyme that has a very critical role in the process of DNA replication and DNA repair. There are two different things going on when DNA is replicated. Let's revisit this process very briefly. As you may remember, our DNA is formed of two complementary strands of DNA that are linked together in a double helix. The strands of DNA are antiparallel, meaning that they are parallel to each other, but in the opposite direction. DNA helicase opens the DNA so that both strands are exposed. During the process of replication, this double helix is unwound, and nucleotide bases are added to both strands going in the 5' to 3' direction.

One strand is continuous while the other is composed of fragments of DNA
Picture of Okazaki Fragments

For one strand, a new continuous strand of DNA is synthesized. For the other strand, small fragments of DNA are synthesized as more and more of the DNA is opened and replicated. These fragments are called Okazaki fragments. Since the DNA is not one continuous piece at this point, something has to be done in order to make it into one continuous piece. This is where DNA ligase comes in. DNA ligase makes the DNA continuous by using the template strand to fill in the complementary bases.

The Role of DNA Ligase

Let's look at this from a different standpoint for a minute. There are many times when construction crews may work towards creating new roads for us to drive on. These roads may be a combined effort between multiple states. Each state would work on the portion of the road that lies within their state and then stop. This would cause many different pieces of the road to be built, rather than one continuous road. Bridges would then have to be built in order to connect the different pieces of the road, making one continuous road that we could drive on. DNA ligase is similar to the construction crew that builds the bridges.

DNA ligase builds bridges in DNA
Picture of bridge

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