Copy the following simplified drawing of a DNA replication fork:
a. On the drawing, indicate the direction of synthesis of the new strand labeled A and the location of DNA polymerase on the strand.

Question

Copy the following simplified drawing of a DNA replication fork:

a. On the drawing, indicate the direction of synthesis of the new strand labeled A and the location of DNA polymerase on the strand.

Accepted Answer

All right. Hello everyone. So this question is asking us to consider the following DNA replication fork encircle the location of the DNA polymerase on strand a determine the direction of synthesis on strand A. So first let's go ahead and analyze this diagram and acknowledge where the replication fork actually its. So in this diagram of the replication fork, we can see two strands of DNA. Now towards the left side, we can see that this DNA is double stranded. And then towards the right side, we can see that the original two strands of DNA have since been separated into single strands. Right? At some point, there is one specific location where that double stranded DNA and the single stranded DNA converge. Now the enzyme that's responsible for this separation of the double stranded DNA is known as helicase. And so the unwinding action of helicase create what's known as an origin of replication. So here this exact branch point where the double stranded DNA and single stranded DNA meet is known as the replication for because it's almost a benchmark of sorts, right? It is the marker to let you know where replication is taking place because that's where the double stranded DNA was unwound. So once you've separated these initial two strands, you have two separate template strands where DNA takes or DNA replication takes place after that's completed, you end up with two new double helices, one strand being from the original copy and the other strand having been synthesized by DNA polymeric. Now DNA polymeric as the name implies, is responsible for generating new DNA. And so it generates new DNA using its template as a reference. Now, when talking about DNA polymerase, there's one interesting bit of nuance that we have to talk about because recall that double stranded DNA has once again two strands of DNA that run in opposite directions, one of them runs from three prime to five prime and the other runs from five prime to three prime. So when DNA polymerase is generating that new strand of DNA, it's only going to do so in the five prime to three prime direction. So let's go ahead and break down how this works in the context of the replication fork. Let's take for example, the template strand that's towards the top of the diagram. We can see based on the labels that it's running from three prime to five prime. Now strand A is the newly synthesized DNA strand that is complementing this template strand running from three prime to five prime. Therefore, strand A is running from five prime to three prime because it should run in the opposite direction as the other strand. And so because of this, we can see that DNA polymerase is not going to be interrupted as it is synthesizing strand. A because strand A is running alongside or in the same direction as DNA polymerase synthesizes DNA, right. So there's no interruption there, but the same cannot be said for the other template strand. Because here, when looking at the other template strand towards the bottom of the diagram, we can see that it's running from five prime to three prime. This means that its complementary strand has to be running in the opposite direction from three prime to five prime. So while in strand A, you have DNA polymerase moving towards the left at the bottom. Here, DNA polymerase is actually moving to the right because again, it can only make DNA from five prime to three prime. So because of this difference in how DNA polymerase is able to perform its function strand A is known as the leading strand, whereas the other strand is known as the lagging strand. And so with that in mind, we've arrived at our final answer because going back to strand A for just a moment because strand A is being synthesized from right to left, that is the direction of synthesis. And the reason why we can also confirm that this is indeed the leading strand is because the direction of synthesis is actually going towards the replication for because we can see it's approaching that point where the double stranded DNA becomes single stranded. So that's the direction of synthesis. And so at this point, because strand A is already rather long as it's approaching the replication fork, DNA polymerase is going to be towards the end. So here I'm drawing out this red oval that represents DNA polymerase and there you have it. So with that being said, we've arrived at our final answer. So if you watch this video all the way through, thank you so very much. And I hope you found this helpful.

Copy the following simplified drawing of a DNA replication fork:

a. On the drawing, indicate the direction of synthesis of the new strand labeled A and the location of DNA polymerase on the strand.

Verified video answer for a similar problem:

Key Concepts

DNA Replication Fork

Direction of Synthesis

DNA Polymerase