In this video, we're going to begin our lesson on DNA Polymerases. And so it turns out that the primary enzyme that's responsible for building new DNA strands are actually these DNA polymerases. You can actually see the function of this enzyme here in its name. And so you can see that anything that ends in ASE is going to be an enzyme, as we discussed in our previous lesson videos when we first introduced enzymes. These are going to be enzymes that polymerize or build DNA. DNA polymerases are going to be the primary enzyme responsible for building new strands of DNA. Now, organisms tend to contain multiple types of DNA polymerases, and these different types of DNA polymerases will have slightly different functions. Moving forward, we're not going to talk about all of the different types of DNA polymerases. We're only going to focus on the most important DNA polymerases involved directly with DNA replication. New DNA strands that are built by these DNA polymerases are always going to be built in the same direction from the 5' end of the DNA molecule to the 3' end of the DNA molecule. These new DNA strands are always being built from their 5' end to the 3' end or direction, is going to be something that's consistent with all DNA polymerases. The new DNA strands are always going to be elongating from its free 3' hydroxyl group or OH group. Recall from our previous lesson videos that the 3' end of the DNA strands has the free hydroxyl group or OH group, and that is what's required to elongate the DNA strand, and we'll talk more about this requirement in our next lesson video. What you'll notice is down below over here, we're showing you this image, and this image is, basically a little cartoon to help you remember that new DNA strands are always elongated from 5' to 3'. Notice that this guy over here is the boss, and he's saying, "Hey, poly or polymerase, can you work an extra shift today?" And the worker over here, the DNA polymerase, is saying, "Boss, you know I only work from 5' to 3'. I don’t work any other shifts." Hopefully, this little creative image here can help you remember that new DNA strands are always built from 5' to 3' and never in the opposite direction from 3' to 5'. To remind you a little bit of DNA structure here, remember the DNA structure consists of these 2 strands of nucleotides that are anti-parallel with respect to each other. They go in opposite directions in terms of their 5' and 3' ends. Notice that the 5' end is going to have a free phosphate group for each of them, and the 3' end has the free hydroxyl group. It's the free hydroxyl group that is required to elongate new DNA strands. And so, the new DNA strands can only be built in this direction, from 5' to 3'. This here concludes our brief introduction to DNA polymerases, and we'll continue to talk more about DNA polymerases and their requirements as we move forward in our course. So I'll see you all in our next video.
DNA Polymerases: Study with Video Lessons, Practice Problems & Examples
Created using AIDNA polymerases are essential enzymes that synthesize new DNA strands by adding nucleotides in a 5' to 3' direction, requiring a template and an RNA primer for initiation. In prokaryotes, DNA polymerase III is the primary enzyme for elongation. Methylation of adenine and cytosine on the template strand allows DNA polymerase to distinguish between old and new strands during replication. Understanding these processes is crucial for grasping DNA replication and its regulatory mechanisms.
DNA Polymerases
Video transcript
DNA Polymerases Requirements
Video transcript
In this video, we're going to talk about some DNA polymerase requirements. In prokaryotic organisms, we know that there are multiple DNA polymerases that can have slightly different functions from our previous lesson videos. We're not going to talk about all of the different types of DNA polymerases, but what you should know is that in prokaryotes, it's specifically DNA polymerase III, written with a Roman numeral III, which is actually the primary enzyme for elongating or building new DNA strands. Notice in our image down below here, we're showing you DNA Polymerase III.
It turns out that all DNA polymerases have 2 central requirements that are necessary for them to operate. We've got these 2 central requirements listed down below, numbers 1 and 2 right here. The first central requirement for all DNA polymerases is a template. All DNA polymerases require a template, and the template is really just referring to the old or parental DNA strand that's going to act as a guide for building the new strands. Notice that the template strand is the strand down below here, the old DNA template strand.
The second requirement that all DNA polymerases require is a primer. A primer is really just a small RNA molecule that acts as the starting point for DNA polymerase. DNA polymerase requires a free 3 prime hydroxyl group and can only extend existing strands. It cannot actually build brand new DNA molecules from scratch. It requires: 1, a template, and 2, a primer as a starting point so that it can provide the free 3 prime hydroxyl group that's needed for DNA polymerase to elongate or extend the new DNA strand. The primer is built by the enzyme primase, which builds the RNA primer. Notice that we're showing you the primase enzyme up here, and its job is to build this primer, this RNA primer. The RNA primer acts as a starting point for DNA Polymerase III, providing a free 3 prime hydroxyl group, which is needed for DNA polymerase III to extend the strand. As it extends, it's going to be base pairing those free nucleotides that come in with the template strand, which is how it knows what nucleotides to replace. Ultimately, the RNA primer is going to be converted to DNA, and the DNA will be part of the newly built DNA strand. We'll talk more about the enzyme that replaces or converts the RNA to DNA, DNA polymerase I, a different DNA polymerase, later in our course.
This concludes our lesson on DNA polymerase requirements that DNA Polymerase III is the primary enzyme that builds these new DNA strands, and it has two central requirements. It requires a template strand, and it requires a primer so that the primer provides the starting point for it to elongate the new DNA strand. We'll be able to get some practice applying these concepts and learn more about DNA replication as we move forward in our course. So I'll see you all in our next video.
If the sequence of the 5'-3' strand is AATGCTAC, the complementary sequence has the following sequence:
DNA Polymerase Distinguishes Template from New Strand via Methylation
Video transcript
In this video, we're going to talk about the ability of DNA polymerase to distinguish the old template DNA strand from the newly built DNA strand via methylation. Over time, Adenine and Cytosine bases, specifically on the old DNA strands or the template DNA strands, are methylated via regulatory processes within the cell. Methylation refers to the addition of a methyl group, a specific type of functional group characterized by a CH3 , 1 carbon and 3 hydrogens.
During DNA replication, the DNA polymerase has the ability to distinguish the old template DNA strands from the newly built strand. The reason the DNA polymerase can distinguish these two strands is because the template DNA strand, the old template DNA strand, is methylated, whereas the newly built strand is not yet methylated, but it will become methylated once again over time. If we take a look at our image down below, we can get a better understanding of how methylation is important during DNA replication. Notice on the left-hand side, we're showing you the original DNA molecule where there are 2 old template DNA strands. Notice that each of these old template DNA strands is methylated specifically at cytosine and adenine residues. Really only cytosine and adenine residues are going to be the ones that are most likely to become methylated. And there are methyl groups on the opposite strand as well. Each of these little pink circles that you see represents methyl groups.
In the process of DNA replication, we know that these two DNA template strands are going to be separated and they're each going to serve as a template for building a brand new strand. Once again, the old template DNA strand is going to be methylated. However, the newly built DNA strand is not yet going to be methylated. So we could say that it is not methylated yet. The DNA polymerase has that ability to be able to distinguish the newly built DNA strand from the old template DNA strand just by this methylation process. This is going to be important later down the line, as we start to continue moving forward and talking more about the abilities of the DNA polymerase. But for now, this here concludes our brief lesson on how the DNA polymerase has the ability to distinguish the old template DNA strand from the newly built strand, and it does so via methylation because the template strand is going to be methylated but the new strand will not yet be methylated. We'll be able to get some practice applying these concepts as we move forward so I'll see you all in our next video.
What is DNA methylation?
Why is DNA methylation important in DNA replication?
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What is the primary function of DNA polymerases?
DNA polymerases are essential enzymes responsible for synthesizing new DNA strands by adding nucleotides in a 5' to 3' direction. They play a crucial role in DNA replication, ensuring that genetic information is accurately copied and passed on to daughter cells. These enzymes require a template strand and an RNA primer to initiate the synthesis process. In prokaryotes, DNA polymerase III is the primary enzyme for elongating new DNA strands. Understanding the function of DNA polymerases is fundamental for grasping the mechanisms of DNA replication and its regulation.
Created using AIWhy do DNA polymerases require a template and a primer?
DNA polymerases require a template and a primer to synthesize new DNA strands. The template strand provides the sequence of nucleotides that the polymerase will use as a guide to build the new strand. The primer, a short RNA molecule synthesized by the enzyme primase, provides a free 3' hydroxyl group necessary for the DNA polymerase to start adding nucleotides. Without these two components, DNA polymerases cannot initiate or elongate new DNA strands, as they can only extend existing strands and cannot start synthesis from scratch.
Created using AIHow do DNA polymerases distinguish between old and new DNA strands?
DNA polymerases distinguish between old and new DNA strands through a process called methylation. In this process, adenine and cytosine bases on the old template DNA strands are methylated, meaning they have a methyl group (CH3) added to them. During DNA replication, the old template strands are methylated, while the newly synthesized strands are not yet methylated. This difference allows DNA polymerases to identify the old template strands from the new ones, ensuring accurate replication and repair processes.
Created using AIWhat is the role of DNA polymerase III in prokaryotic DNA replication?
In prokaryotic DNA replication, DNA polymerase III is the primary enzyme responsible for elongating new DNA strands. It adds nucleotides to the growing DNA strand in a 5' to 3' direction, using the template strand as a guide. DNA polymerase III requires a primer to provide a free 3' hydroxyl group to initiate synthesis. This enzyme ensures the accurate and efficient replication of the prokaryotic genome, playing a critical role in cell division and genetic inheritance.
Created using AIWhat is the significance of the 5' to 3' direction in DNA synthesis?
The 5' to 3' direction is significant in DNA synthesis because DNA polymerases can only add nucleotides to the free 3' hydroxyl group of the growing DNA strand. This directional synthesis ensures that the new DNA strand is built in a consistent and orderly manner. The 5' end of the DNA strand has a free phosphate group, while the 3' end has a free hydroxyl group. The requirement for a 3' hydroxyl group for elongation is a fundamental aspect of DNA replication, ensuring the accuracy and efficiency of the process.
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