Steps of DNA Replication - Video Tutorials & Practice Problems
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concept
Steps of DNA Replication Concept 1
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Video transcript
Now DNA replication can be simplified into six steps. Step one involves the enzyme, healer case he a case it binds and unwinds the two strands of the template DNA by breaking hydrogen bonds. If you come down here in the image, we're first going to label the five prime, three prime ends of our DNA template strands. We're gonna say up here is our five prime. And if we found this here, this will be three prime. If this is five prime, this would have to be three prime, this would have to be five prime. Then coming down here. If we follow this, we can see that this trend here would be five prime and therefore this would not be three prime. So these are the ends of our uh DNA strands. We're talking about step one where Hela case is going to cut through our hydrogen bonds between the nitrogenous bases. So we can see here that this hydrogen will not, these hydrogen bonds are broken with a bang by the heli case enzyme. It slices through them, opening up the DNA double helix. So that replication can commence. Now, here for step two, we have our stabilizing uh proteins. Here they're going to bind to and stabilizes the single strand of DNA. Now DNA wants to maintain these hydrogen bonds, but we have the stabilizing proteins which come in and kind of force it to stay open, stay open long enough so that DNA replication can proceed. So here we have our stabilizing proteins. Remember they're represented by these orange spheres. So this would be step two. Next, we have step three, which deals with primate. Our enzyme prima adds the RN A primer to the template DNA so that polymerase can start replicating. Now, if we come down here, here is step three, we have our primates adding down these primers. So we have one here here, here and here. And what's important here is that we're gonna continuously add primers to the lagging strand to make several Okazaki fragments. Remember the lagging strand goes in the opposite direction of the replication fork movement. Because of this, we're gonna have to continuously add primers to make our new DNA strands. And this is just the way it has to be. And if we look, we have Okazaki fragments, remember these Okazaki fragments are just the small p small bits here where we have our primer and a small amount of DNA being laid down with it. So we're gonna say that is three. Now we have DNA polymerase which has two functions. First, it adds new DNA nucleotides in the five prime to three prime direction. So here this would be step four, we're adding in the five prime to three prime direction. So since this is the three prime end and the strands have to be anti parallel in order to be compliment, complimentary, we're gonna say here that this is the five prime to three prime end in which we lay down our new DNA. OK. So this is the DNA polymerase and this is also our DNA polymerase doing the same thing, it's adding down in the five prime to three prime. And right, so this is five prime over here and it's going this way towards three prime. Now, the second function it has is it removes RN A primers and replaces them with DNA. So we're gonna say here, step five, there's this primer here. This polymerase will also replace that poly on that primer in order to add in new DNA. So this pink portion and all these pink portions are eventually going to be removed by D DNA polymerase. And then finally, step six, we have DNA ligase which links Okazaki fragments together on the lagging strand to create a single new DNA strand. Remember there's these gaps that we have between our Okazaki fragments. Step six are ligase comes in, it kind of fills in these gaps here. So we have one strand of new DNA just like we have our leading strand up here. That's all one strand of DNA, right? So when we talk about DNA replication, we could talk it, talk about it in reference to these six major steps which incorporates different enzymes and proteins in order for DNA replication to be successful. So again, just remember from Hela case all the way down to like gates, they all have a job in order to get new DNA, new daughter strands to be created from our DNA template strands.
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example
Steps of DNA Replication Example 1
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1m
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Video transcript
In this example question, it says DNA polymerase can join new nucleotides only to the end of a pre-existing strand. So we're talking about the primer and the strands are anti parallel. This will provide the basis of, well, think about what DNA polymerase does. It's going to help add new DNA strands. These new DNA strands can come in the form of leading and lagging strands. Now, here we take a look. It does more than just leading strands. Yes, it can have the formation of Okazaki fragments which are the individual parts of the lagging strand does more than that. The formation of the ori no, the origin of replication. That's not what DNA polymerase does both leading and lagging strands of DNA. Yes. Again, Pulmonary says too has a function of adding new DNA. This comes in the form of either leading strands or lagging strands. Remember if we're looking at one individual lagging strand that represents an Okazaki fragment. So really by saying lagging strands, we're including Okazaki fragments as well. So this is our answer. If we look at the last one, it says DNA ligase and stabilizing proteins, those are other enzymes and other proteins, they work independent, they work in conjunction with DNA polymerase. They are not responsible for what polymerase does they have their own separate functions. So this would not be a good example, would not be a good answer. So here, the answer is option D.
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Problem
Problem
Which of the following statements correctly describes the difference between the leading and the lagging strands of DNA during DNA replication?
A
The leading strand is synthesized by adding nucleotides to the 3' end of the growing strand, and the lagging strand is synthesized by adding nucleotides to the 5' end.
B
The leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction.
C
The lagging strand is synthesized continuously, whereas the leading strand is synthesized in short fragments that are ultimately stitched together.
D
The leading strand slows its rate of replication so that the lagging strand can catch up.
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Problem
Problem
Below is a close-up of the portion of a DNA replication bubble.
Helicase is shown as a yellow triangle currently moving from left to right. Based on what you know about the creation of new DNA during replication, which is the lagging strand and why?
A
A is the lagging strand, as DNA is always synthesized in the 5' to 3' manner.
B
B is the lagging strand, as DNA is always synthesized in the 5' to 3' manner.
C
A is the lagging strand, as DNA is always synthesized in the 3' to 5' manner.
D
B is the lagging strand, as DNA is always synthesized in the 3' to 5' manner.
E
It is impossible to tell, with the information provided.
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