In this video, we're going to talk more about step 1a in the steps of DNA cloning, which is using restriction enzymes. Recall that restriction enzymes are enzymes themselves that are specifically important for cleaving or cutting the DNA at these specific locations called restriction sites on the DNA, and that is going to produce sticky ends. We will define restriction sites and sticky ends down below in our text. Restriction sites are really just defined as specific sequences of DNA where a restriction enzyme will bind and cut the DNA. These restriction enzymes don't just bind and cut any region of the DNA. They only bind to very specific regions of the DNA and only cut very specific regions of the DNA called restriction sites. Of course, once that DNA has been cut at the restriction site, it produces sticky ends, and sticky ends are really just a single-stranded DNA overhang that is going to be produced from the restriction digestion reaction. We can get a better feel for this down below in our image, looking at restriction enzymes and restriction sites along with sticky ends.

Notice over here on the left-hand side, what we have is a specific DNA molecule here, and this DNA molecule has a very specific region called the restriction site, and this specific region is going to have a very specific DNA sequence that is going to be recognized by the restriction complex enzyme that is going to be binding to the restriction site and cutting the restriction site. When these restriction enzymes cut at the restriction site, they usually generate these sticky ends and so they create a staggered type of cut in the DNA. Notice that the DNA is being cut in this kind of staggered way, and when it's cut in this staggered way, it creates these overhangs, these single-stranded DNA overhangs that are kind of sticking out of the rest of the molecule. These are the sticky ends that we are referring to. The reason that they're called sticky ends is because they can still complementary base pair to other matching sticky ends as we'll talk about moving forward in our course. But for now, this here concludes our brief lesson on step 1a, using restriction enzymes, and how restriction enzymes will bind and cut restriction sites to generate sticky ends and separate molecules. We'll be able to get some practice applying these concepts and talk more about step 1b as we move forward. So, I'll see you in our next video.