in this video, we're going to begin our introduction to DNA replication. And so it's important to keep in mind as we move forward in our course and continue to talk Mawr and Maura about DNA replication, that there's actually much more information that is known about pro carry ah, tick DNA replication. Then there is information known about eukaryotic DNA replication. And so, for that reason, as we move forward in our course, were mainly going to be focusing on pro carry ah, tick DNA replication. However, it is also important to keep in mind as we move forward in our course that scientists believe that most of the DNA replication process is fundamentally similar in both pro Kerasiotes and eukaryotes. And so, even though moving forward in our course were mainly gonna be focusing on pro carry attic DNA replication, it's important to remember that most of the process is fundamentally similar in both of them. And as we move forward in our course, will try toe point out some of the key differences between pro Cariou pro carry attic and eukaryotic DNA replication. But in both pro carry attic and eukaryotic DNA replication, DNA replication occurs via a semi conservative process, which again we introduce what semi conservative DNA replication waas in our last lesson video. And so again, semi conservative DNA replication suggests that the old parental strands in the original DNA molecule are going to separate from one another. And they're each going to act as templates in the synthesis of new DNA strands that air complementary to the old parental strands. And so, if we take a look at our image down below, what we're showing you is another image of semi conservative DNA replication. So notice over here on the far left, we start with just one DNA molecule. This is the original DNA molecule, and by the end of this DNA replication process, we end up with two DNA molecules one here and one here. And so the way that this DNA replication works is that the DNA strands and the old parental DNA molecule are going to separate from one another. And so you can see the separation here is beginning. And so, as these old original DNA strands separate from one another, they act as templates to build new DNA that's complementary to it. And so you could see the new DNA. Here is this yellow strand that's being built using the old Blue Strand as a template. And so this process will continue and continue. And ultimately it results in two DNA strains that are identical to each other and identical to the original, since it's building via complimentary base pairing. And again we'll be able to talk more and more about the mechanism of this semi conservative DNA replication as we move forward in our course, and we'll start off by introducing the DNA replication components. And so I'll see you all in our next lesson video to talk about that.
Components of DNA Replication
Play a video:
Was this helpful?
in this video, we're going to briefly introduce some of the most important components of DNA replication. And so it turns out that DNA replication is actually a relatively complex process that requires, ah, host of multiple enzymes and proteins working together. And so notice down below. We have this table that shows you some of the most important enzymes and proteins involved in DNA replication, along with their functions. Now it's important to note here in this video we're on Lee going to briefly introduce these enzymes and proteins and their functions. But as we move forward in our course in their own separate videos, we're going to talk about each of these enzymes and proteins and mawr detail, along with the details of their functions. And so again, keep in mind that this is just a brief introduction and so you can use this table down below as a reference, moving forward as we cover these different enzymes and proteins in more detail. And so what you'll notice is over here in this column we're going to show you is the shape that we're going to use here in clutch prep to represent each of the individual enzymes and proteins. And then, of course, we have the name of the enzyme and protein in this column. And then we have the function of the enzyme, a protein in this column here. And so the first enzyme enzyme that we're showing you here is going to be topo Aissami race and topo Aissami races, also sometimes referred to as DNA guy race in pro Kerasiotes. And so you may see your textbooks or your professor refer to it is that and its function is to relieve DNA super coiling ahead of the replication fork. And again, we'll talk more about what DNA super coiling is in the function of topo I summaries and DNA iris in their own separate video as we move forward. And that again goes for all of these enzymes and proteins. And so the next enzyme that we're showing you is represented with this yellow triangle here here, a clutch prep, and it is a healer case, and he'll cases function is to unwind DNA double helix at the replication fork. Next we have are these little orange circles, and these represent our single stranded, binding proteins. And as their name implies, these single stranded binding proteins they're going to bind to and stabilize single stranded DNA. Now, next, what we have is this pink structure which is going to be the primates. And as the primates employees, um, name implies it is going to create RNA primers, which act as a starting point for DNA synthesis. Next, what we have is this light blue circle here which represents DNA prelim arrays, three in pro carry attic organisms. And this is the main DNA pull Emery's that's responsible for building a new strand of DNA, using the old strand of DNA as a template. But there are multiple DNA prelim A races, and this DNA prelim a race is going to be DNA proliferates one and pro corrodes, and its job is to replace our primers with DNA. Now, notice that DNA polymerase too, is not mentioned here on this list. And that's because DNA polymerase, too, is not one of the most important components of DNA replication. And it has a slightly different function that we're not really going to cover in this course now. The last protein, the last component that's very important for DNA replication, is going to be DNA like Jace and DNA lie Jace is function is to co violently join together what are known as Okazaki fragments in the lagging DNA strand. And again, this will make a lot more sense these functions. And, uh uh, these enzymes and proteins will be cleared up as we move forward and talk about them in more detail in their own separate videos. But again, this year concludes our brief introduction to some of the most important components of DNA replication that we're going to encounter moving forward. And again, we'll be able to talk Maura about thes as we move forward in our course. So I'll see you all in our next video.
Origin of Replication
Play a video:
Was this helpful?
in this video, we're going to introduce the origin of DNA replication or just the origin of replication. And so DNA replication actually begins at a specific set of DNA sequences that air collectively referred to as the origin of replication or just the Ori for short. And so it turns out that pro carry attic cells have a small circular chromosome, and these small circular chromosomes of pro carry attic organisms have just one single origin of replication on their chromosome, whereas eukaryotic organisms have larger linear chromosomes, and these larger linear chromosomes of eukaryotes actually have multiple origins of replication. In some cases, they can have up to hundreds of origins of replications, orm or and so if we take a look at our image down below notice on the left hand side. Over here, what we're showing you is pro carry. Ah, tick DNA replication. And on the right hand side over here, what we're showing you is you carry attic DNA replication, and what you'll notice is that the chromosome of pro Kerasiotes is circular and the circular chromosome of pro carry it's on. Lee has just one single origin of replication, one origin of replication Now, if we take a look over here at the Eukaryotic chromosome, noticed that its chromosome is linear and it's the linear chromosome actually has two origins of replication in this image, but again, they can have many origins of replication. So multiple origins of replication. And so what you'll see here is that the darker blue molecules represent the old original parental DNA strands. And as DNA replication proceeds, uh, it's going to occur and begin at this origin of replication. And so what you'll notice here in this image is that the new DNA strands are in the light blue color. And, of course, thes little pink structures are representing RNA primers, which we're going to talk Maura, about the functions of these RNA primers, Um, as we move forward in our course. But the point here is that the origin of replication is where DNA replication is going to begin the process. And so you can see over here, uh, in the eukaryotic DNA replication image that once again, the origin of replication is going to represent the starting place where DNA replication is going to begin and proceed. And so this here concludes our brief introduction to the origin of replication this, uh, set of DNA sequences that marks the beginning of DNA replication. And we'll be able to talk more and more about DNA replication as we move forward in our course. So I'll see you all in our next video.
Play a video:
Was this helpful?
in this video, we're going to introduce Replication Forks. And so recall from our last lesson video that DNA replication begins at a specific set of DNA sequences called The Origin of Replication, or just the Ori for short. And so it turns out that many different proteins are going to bind to this origin of replication. And those proteins are going to separate the two strands of DNA unwinding the DNA so that DNA replication can begin. And this unwinding forms a replication fork, which is sometimes also referred to as a replication bubble. And so replication forks are really just these Why shaped regions that are at the end of the bubble, where DNA is unwound and so we'll be able to see the replication forks down below here in our image. And so if we take a look at this image, which you'll notice is here, over here on this side, we're showing you this replication forks, and so you can see that the DNA strands have unwound. So we have the old original DNA strand. Are these darker blue color and which will see is that they're starting to be separated Here. There's a separation of these two strands, and the separation of these two strands creates the replication, forks or the replication bubbles. And so what you'll notice is that at each of these positions on each side of this, unwinding is a replication fork. So the replication forks are indicated with these yellow backgrounds that you see here and over here, and you'll notice that they are these why shaped regions that they kind of create these the sideways. Why right here and the sideways? Why is the replication fork? And you'll also see the sideways? Why over here? And so that's why we call these replication forks thes. Why shaped regions at the end of the bubble where DNA's unwound and you'll notice that it does kind of create somewhat of a bubble. So from here to here, there's a little bit of a bubble, and so sometimes it's referred to as the replication bubble. And so what you'll notice here is that DNA replication eyes actually going to proceed by directionally and by directionally just means that it's going to occur in both directions at each replication for and so you'll see that the direction of DNA replication on the replication for is gonna be indicated by these red arrows. And so DNA replication is going to proceed in this direction at this replication for And it will also proceed in this direction for this replication for ca's well, and so that's important to keep in mind moving forward because we're going to talk about DNA replication and just one replication for But we have to keep in mind that DNA replication occurs that the other replication fork in the same in the opposite direction. And so DNA replication proceeds by directionally in both directions at each replication. For And so once again, we're gonna talk, Maura about the process of DNA replication, uh, involving these RNA primers and thes different strands as we move forward in our course. But for now, this here, uh, concludes our video, introducing the terms replication forks, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video
Which of the following is incorrect regarding DNA replication forks?
DNA replication forks begin forming at the origin of replication (ORI).
DNA replication forks are caused by helicase separating two complementary strands of DNA.
There are two replication forks found in each replicating prokaryotic chromosome.
DNA replication forks are found at both ends of the replication “bubble”.
None of the above are incorrect.
Unwinding the DNA: Topoisomerase, Helicase & SSBs
Play a video:
Was this helpful?
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.
What is the function of the enzyme topoisomerase in DNA replication?
Relieving strain in the DNA ahead of the replication fork caused by the untwisting of the double helix.
Elongating new DNA at a replication fork by adding nucleotides to the existing chain.
Reattaching the hydrogen bonds between the base pairs in the double helix.
Building RNA primers using the parental DNA strand as a template.
Additional resources for Introduction to DNA Replication