Unwinding the DNA: Topoisomerase, Helicase & SSBs

by Jason Amores Sumpter
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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 topo I summaries and he'll a case as well as the proteins single stranded, binding proteins, or SBS. And so it turns out that several different proteins participate in the unwinding of the DNA during DNA replication. And, of course, the unwinding of the DNA is just referring to the separation of the two strands of DNA. And so these include the proteins, these three proteins that are listed down below 12 and three. And the first of these three is topo ice armories, which is also sometimes referred to a DNA guy raise and precarious and topo I summaries Ordina Guy raise its function is to cut and rejoin the DNA in order to relieve strain that's caused by DNA super coiling. And so DNA, super coiling or just super coiling can actually inhibit DNA replication and therefore super coiling must be relieved in order for DNA replication to proceed normally. And so if we take a look at our image down below, over here on the left were showing you some DNA super coiling here so you can see that we're showing you a DNA molecule. But the DNA molecule here is super coiling. And so this structure that you see here is a DNA super coil. And so the DNA super coil is going to again cause strain, and it can inhibit DNA replication. And so this DNA super coil must be relieved in order for DNA replication to proceed. And that is the function of the DNA guy race or the topo I summaries, which is right here ahead of the replication fork over here. And so the DNA guy raise its job is to again eliminate or remove the DNA. Super coils and the DNA super coiling kind of represent can be better understood by thinking about the super coiling of one of these old telephone wires. And so this old telephone wire will super coil, just like the DNA molecule has a tendency to super coil. And so the topo ice armories is going to help with getting rid and eliminating the DNA Super coils. Now the second protein involved with the unwinding of the DNA is hell a case and he'll a case unwinds the DNA by breaking hydrogen bonds and the hydrogen bonds are forming between the two DNA strands. And so when he'll case breaks these hydrogen bonds between the two strands, it separates the strands. So he'll a case is going to help to create a single stranded DNA. And so if we take a look at our image down below, which you'll notice is that the healer cases represented as this yellow triangle and its job is to break the hydrogen bonds that hold the two DNA strands together. And so it separates the two DNA strands creating single stranded DNA. And this is where the third proteins come into play the single stranded binding proteins, which are abbreviated as just S s bees. And so these single stranded binding proteins, or S S B s are going to bind to the single stranded DNA to prevent the RIA kneeling of the DNA to prevent those hydrogen bonds from reforming. And they're also going to prevent the degradation of each of these single stranded DNA molecules. Since single stranded DNA within cells tends toe be degraded. And so these single stranded, binding proteins will bind to the single stranded DNA prevent ria kneeling and degradation of each of the separated DNA strands. And so when we take a look at our image down below, noticed that the single stranded, binding proteins are these orange circles here that are binding to the single stranded DNA that's being separated here. And so 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. And so this year concludes our lesson on the unwinding of the DNA. Uh, and we'll be able to get some practice applying the concept that we've talked about here as we move forward in our course, so I'll see you all in our next video.