In this video, we're going to talk about some of the enzymes and proteins involved with the unwinding of the DNA during DNA replication, and these include the enzymes topoisomerase and helicase, as well as the protein single stranded binding proteins or SSBs. It turns out that several different proteins participate in the unwinding of the DNA during DNA replication. Of course, the unwinding of the DNA just refers to the separation of the 2 strands of DNA. These include the proteins, these 3 proteins that are listed down below, 1, 2, and 3, and the first of these 3 is topoisomerase, which is also sometimes referred to as DNA gyrase in prokaryotes. Topoisomerase or DNA gyrase, its function is to cut and rejoin the DNA in order to relieve strain that's caused by DNA supercoiling.
DNA supercoiling or just supercoiling can actually inhibit DNA replication and therefore supercoiling must be relieved in order for DNA replication to proceed normally. If we take a look at our image down below, on the left, we're showing you some DNA supercoiling here. You can see that we're showing you a DNA molecule, but the DNA molecule here is supercoiling and so this structure that you see here is a DNA supercoil. The DNA supercoil is going to, again, cause strain and it can inhibit DNA replication, and so this DNA supercoil must be relieved in order for DNA replication to proceed. That is the function of the DNA gyrase or the topoisomerase which is right here ahead of the replication fork over here.
The DNA gyrase's job is to again eliminate or remove the DNA supercoils. The DNA supercoiling can be better understood by thinking about the supercoiling of one of these old telephone wires. This old telephone wire will supercoil just like the DNA molecule has a tendency to supercoil. The topoisomerase is going to help with getting rid of and eliminating the DNA supercoils. Now the second protein involved with the unwinding of the DNA is helicase, and helicase unwinds the DNA by breaking hydrogen bonds.
The hydrogen bonds are forming between the 2 DNA strands. When helicase breaks these hydrogen bonds between the two strands, it separates the strands. So helicase is going to help create single stranded DNA. If we take a look at our image down below, what you'll notice is that the helicase is represented as this yellow triangle, and its job is to break the hydrogen bonds that hold the 2 DNA strands together. It separates the 2 DNA strands creating single stranded DNA.
This is where the third proteins come into play, the single stranded binding proteins, which are abbreviated as just SSBs. These single stranded binding proteins, or SSBs, are going to bind to the single stranded DNA to prevent the reannealing of the DNA, to prevent those hydrogen bonds from reforming. They're also going to prevent the degradation of each of these single stranded DNA molecules since single stranded DNA within cells tends to be degraded. These single stranded binding proteins will bind to the single stranded DNA, prevent reannealing and degradation of each of the separated DNA strands. When we take a look at our image down below, notice that the single stranded binding proteins are these orange circles here that are binding to the single stranded DNA that's being separated here.
These are the proteins that are going to be important for the unwinding of the DNA and the separation of the two strands of DNA so that they can serve as templates for building the brand new DNA strands. This here concludes our lesson on the unwinding of the DNA, and we'll be able to get some practice applying the concepts that we've talked about here as we move forward in our course. So I'll see you all in our next video.
