Intro to DNA Replication - Video Tutorials & Practice Problems
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Intro to DNA Replication Concept 1
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Hey, everyone. So in this video, we're gonna talk about the beginnings of DNA replication. Now under DNA replication, a template strand is used to synthesize a new DNA strand that is complementary to it. Now, here we're going to say that our template strand, well, this is just the starting or parent strand that is copied during replication. So if we take a look here, our template strand is this right here and this is actually a DNA double helix made up of two template strands. We we're gonna say our complimentary or our daughter strand. Well, this is the newly synthesized strand of DNA copied from the template strand. So here we have our DNA double helix made up of two template strands. Those nitrogen spaces are linked together. Remember by hydrogen bonds, what happens is we start to cut through these hydrogen bonds and unwind the DNA exposing the template strands. So here are two step template strands exposed, the nitrogenous spaces are no longer hydrogen bonded. And what we start doing is we start copying these exposed template strands. We can see this growing green strand here and this growing green strand here we're copying the exposed template strands over time, we just keep going higher and higher up. The DNA double helix is becoming more and more unwound and our daughter strands are growing and growing eventually. What we'll get at the end is two DNA double helix. And if you can, if you see, we see that they are a mixture of what our template strand and our daughter strength. We're gonna say that the two new DNA double helix or double helices that were created. We're gonna conserve some of our old DNA. This is what we call the semiconservative model where we say both double helices are gonna have one template strand and one daughter strength. So in that way, you kind of retain some of the old DNA we had in the very beginning, the starting or parents strand is still present in both double helices as well as our newly copied daughter strands, right? So just remember when we're talking about DNA replication, we're talking about the semiconservative model.
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example
Intro to DNA Replication Example 1
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In this example question, it says which of the following statements most accurately describes DNA replication A. It's a semiconservative with all of the DNA copied and is restructured with both new double hela seeds, right? So if we look at all these options, we can see that this says semiconservative, dispersive, semiconservative and conservative. From what we said earlier, we know that DNA replication follows a semiconservative model. So we know the answer is gonna be either A or CB is out. D is out. So what's the difference between A and C? Well, again, A says it is a semiconservative with all of the DNA copied is restructured within both new double helotes. OK. C says it is semiconservative with the template strand being found within both double helos here. The better answer is option C remember we're going to copy the template strand to create our complementary or daughter strand. At the end, we'll have two DNA double helices each with one template strand and one daughter strand here. This is saying that the template strand will be found within both new double helices. This is true. So here sees the better answer and see would be our final answer.
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concept
Intro to DNA Replication Concept 2
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2m
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Now, when we talk about DNA replication, we're going to say that it requires a host of multiple enzyme slash proteins working together. Here, we've compiled the list of the most important enzymes and proteins necessary for DNA replication. First, we're gonna start out with heli case heli case is an enzyme and we'll display it as a triangle that is yellow. Its job is to unwind the DNA double helix and it does it at the replication form. We'll talk about the replication for it later on as kind of a landmark that we find when we're talking about DNA replication. Now, when we say unwind, remember it's cutting through our hydrogen bonds between the nitrogen and spaces in order to expose our template strands for replication. Next, we have what are called stabilizing proteins. Here, destabilizing proteins, we're gonna depict them as these orange balls here. Their job is to basically uh they're gonna bind to and stabilize the single strand of DNA. Now DNA wants to be in a double helix form. We need this protein to basically keep it open so that our replication can start, we can start to copy our template strands to produce our daughter strands. Next, we have what's called our prima, which we're depicting as this image here. This pink mag magenta type color here. Its job is to create R and A primers as a starting point to replication. Next, we're gonna have this bluish figure. This is our DNA polymerase. Now, what is its job? Well, it creates a new DNA strand using the template strand of DNA. So its job is to make our complimentary or daughter strand. And then finally, we have DNA ligase here. What it does here is it's going to join, so it joins together new strands of DNA. So again, it's all of these enzymes and proteins working in conjunction with one another that allows us to do DNA replication. Here. We're just talking about what they resemble what their names are and what their function will be. Later on. When we're talking about DNA replication, we'll see how the process actually happens, right? So, keep in mind these important enzymes and proteins.
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concept
Intro to DNA Replication Concept 3
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3m
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Hey, everyone. So in our continued discussion of DNA replication, we can say that replication begins with hela case, unwinding DNA at a specific site called the origin of replication. Now, this origin of replication or, or I or or I, this is basically where he locates the sides where it wants to cut into the hydrogen bonds between our nitrogenous spaces. This typically happens when it's scanning for a specific sequence of nucleotides and that's where it starts to cut. So if we take a look here, we'd say that this orange box that is on top of this phosphate sugar backbone of our DNA double helix represents our origin of replication. You can see here we have a hela case and it looks like it's moving this way and another hela case that's moving this way, they are bending and then breaking these hydrogen bonds that are connecting the different nitrogenous spaces together. Now, here we're going to say that our two strands of DNA are separated forming what we call two replication forks. These replication forks are y shaped regions at each end of the bubble or DNA is unwound. Now, if we take a look here we still have our origin of replication here. We have our hela case here. In our hela case here, they're just continually to cut through the hydrogen bonds, opening up our DNA double helix where we have this gap. Now, this empty space in here replica um represents our replication bubble. And we're gonna say that the regions that are highlighted in yellow. Well, those are our replication forks. Remember we say they are Y shaped regions. If you look kind of looks like A Y, it's like a Y here too. So they are Y shaped regions. Now DNA replication proceeds bidirectionally in both directions. So as you can see here, we have our old DNA in blue and then we have our new DNA being laid down. Once we've opened up the double helix, we can see that DNA is being laid down in this direction and DNA is being laid down in this direction. We also see that we have a magenta tail. That's our RN A primer which remember RN A primers are put down by our enzyme primates that first has to be put down before our new DNA can start being put down complementary to the DNA template strands, right? So just remember when we're talking about replication forks, we're talking about this region highlighted in yellow looks like A Y. It's being created by heli case just continuously moving down the double helix and cutting through the hydrogen bonds that connect the nitrogen and spaces together, opening it up creates replication bubble which then allows new DNA to come in and start being laid down on the DNA template strands. With this new DNA, we have DNA replication.
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example
Intro to DNA Replication Example 2
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1m
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Which of the following is incorrect. Regarding DNA replication forks, DNA replication forks begin forming in at the origin of replication or the ori that's true. He like he come there and then they start cutting through and we're starting to form replication forks right then. And there DNA replication forks are caused by heli case separating two complementary strands of DNA. That is true. The two strands of DNA are complementary to each other, they run anti parallel to each other. So this is true. There is one replication fork found for every replication bubble formed. So remember we have our replication bubble, right. So we have our replication bubble that's formed. We know that this region here and this region here represent our replication forks and we know we have our or I or origin of replication there. From this image, we can see that one replication bubble as associated with it. Two replication for its. So this statement is incorrect. It's not one replication fork for every replication bubble. It's two replication forks for every one replication bubble. Now DNA replication forks are found at both ends of the replication bubble. We can see that from this drawing that this is true as well. So here, the only statement that's incorrect is option c remember one replication bubble will have two replication forks, one in each end of the bubble.
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Problem
Problem
How many helicase enzymes are needed for a strand of DNA that possess 5 origins of replication?
A
2
B
5
C
6
D
8
E
10
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concept
Intro to DNA Replication Concept 4
Video duration:
5m
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In this video, we continue our discussion of DNA replication in terms of the lagging strand and the leading strand. Now here, after separating the double helix replication creates two new strands, we're gonna say the strand types are dependent on the direction of the replication fork. Here, we have our leading strand and our lagging strand. We're gonna say the leading strand is the continuous replication in the same direction as the replication fork movement and only one RN A primer is required for application. If we come down here and take a look at this image, remember we have our old DNA in blue, our new DNA being laid down in green and then our RN A primer that's being put down by primates to help initiate replication. Now imagine that we have our origin of replication and it's over here, everything that's going on is to the left of that. Right now, we're just paying attention to half of our replication bubble. If we take a look at this, we're gonna look at our leading strand. First, we say that we put down our primer and remember when we're putting down our primer and starting to create new DNA, it always goes in the five prime to three prime direction. So here this is the three prime end of our old DNA. If we're going five prime to three prime, that means we have to lay down our initial primer and then the new DNA on the five prime and of itself, and it's gonna go this way or it's three prime for itself, three prime for itself would correlate to five prime of the old DNA strand. Now, we have our hela case here which is cutting through the hydrogen bonds of our nitrogenous spaces. So this is our replication fork here. Our hela case is moving in this general direction. And so our application fork is moving in that same direction. The leading strand puts down new DNA in that same direction. It's moving this way in the same direction as the hela case and the replication for. So it's as this is becoming more and more open, we're putting more and more DNA down the lying strand though is the opposite. Here. It is a dis discontinuous replication in the opposite direction. As the replication fork movement here, we're gonna create what are called Okazaki fragments. These are small, multiple small replicated segments that require an RN A primer. So if we take a look here, we're gonna say that an Okazaki fragment is just a small segment of new DNA coupled with our primer that's been put down. So we can see that we have 12345 Okazaki fragments shown here collectively altogether. This is what is the lagging strand or a lagging strand is just a collection of Okazaki fragments. Now, how does this work? Well, our replication fork and our hela case is going in this direction, we see that new DNA is being put down in this direction. It's going the opposite way. This indicates a lagging strand. Now, the way it works is as we're opening up this great as we're opening up this DNA helix with our replication bubble being formed, we're putting down a primer. So primer gets laid down here as we open up and then new DNA starts getting created. But then what happens? This thing keeps sliding down this way, opening up the DNA strand even more. And as it ha as it opens up even more, then another primer has to be put down here and new DNA moves forward. So we're basically waiting for this thing to open up so that we could put a primer there and then grow this way. It opens up a little bit further down here. We put another primer, it moves down that way. We're waiting for it to open up even more the DNA double helix. So we could put a primer and then move in the opposite direction. This is gonna cause small gaps in between our Okazaki fragments. Later on, we'll see how we can connect these gaps together at the end of DNA replication. But for now, our lagging strand, it puts down new DNA in the opposite direction of the replication fork movement. This creates these Okazaki fragments and they have small gaps between them. This is different from the leading strand which just continuously puts more and more DNA down as long as it needs to, to make a whole strand of new DNA. It's moving in the same direction as the healer case and the replication fork movement. We don't have these small gaps that we would see in the lagging strand when it comes to the leading strand. All right. So just keep in mind the difference between our leading strand and our lagging strand is really in reference to direction of our replication fork movement and the hela case enzyme.
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example
Intro to DNA Replication Example 3
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1m
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Here, we're told that a newly synthesized leading strand of DNA is given as the following. So from the three prime and we have att CG AC TA A towards the five prime, it says determine the template DNA strand that was copied. So remember this leading strand was copied from our template strand, which is our original or parent strand. So here, remember they need to be anti parallel to one another. So this N will be five prime, this and here will be three prime. And remember this is DNA. So the base pairings are A with T and G with C. So here this is a, so this originally had to be T, this was A and A, this is C. So this was a G, this is a G. So this was AC, this is T, this is a G, this is an A and then this is T and T. So this was our original template DNA strand that was copied to make this leading strand. So this will be our final answer.
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Problem
Problem
Based on the image below, which of the following statements is true?
A
Arrow A represents the lagging strand and moves in the opposite direction of the replication fork movement.
B
Arrow B represents the lagging strand and moves in the same direction of the replication fork movement.
C
Arrow A represents the leading strand and moves in the same direction of the replication fork movement.
D
Arrow B represents the leading strand and moves in the opposite direction of the replication fork movement.
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