In this video, we're going to talk about base excision repair. Base excision repair is a DNA repair mechanism that replaces and repairs damaged nitrogenous bases that may have been damaged through some kind of chemical modification to the nitrogenous base. Base excision repair uses enzymes called glycosylases. These glycosylases can identify the damaged bases and then remove them. Base excision repair occurs in a series of three steps that we have numbered down below in our image. Notice the image below is focusing on base excision repair, which utilizes enzymes known as DNA Glycosylases, represented in this image as a green circle that you see highlighted right here.
The DNA glycosylase enzyme identifies the DNA distortion caused by the damaged nitrogenous base. After it identifies the distortion, you can see that the DNA backbone here is distorted, it will then remove the damaged nitrogenous base. Here you can see that the damaged nitrogenous base is the guanine that's chemically modified. It is being removed, as you see here, by the DNA glycosylase enzyme. Then, another enzyme will come in and cut the sugar phosphate backbone at the site where the damaged nucleobase used to be. Here you can see the enzyme comes in and cuts the sugar phosphate backbone. What happens next is that the DNA polymerase enzyme comes back into play, and its 3' to 5' exonuclease activity removes and then replaces the damaged region of DNA, and DNA ligase will seal it together. Here, the new DNA has been removed and replaced, and now the correct nitrogenous base has been implemented.
This concludes our brief lesson on base excision repair. We'll be able to get some practice applying these concepts and learn about other DNA repair mechanisms as we move forward. So, I'll see you all in our next video.