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, is actually the primary enzyme that's 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, number 1 and number 2 right here. The first central requirement for all DNA polymerases is a template. All DNA polymerases require a template, and the template is just referring to the old or parental DNA strand that's going to act as a guide for building the new strands. If you take a look at our image down below, notice that the template strand is the strand that's down below right here. This is 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' hydroxyl group and can only extend existing strands. It cannot actually build brand new DNA molecules from scratch. It requires, again, number 1, a template, and requires a primer as a starting point so that it can provide the free 3' hydroxyl group that's needed for DNA polymerase to elongate or extend the new DNA strand.
The primer is going to be built by the enzyme primase, and primase is going to be the enzyme that builds the RNA primer. When we take a look at our image down below, 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. That's because the RNA primer provides a free 3' hydroxyl group, and this free 3' hydroxyl group is what's needed for DNA polymerase III to extend the strand. As it extends the strand, it's going to be base pairing those free nucleotides that come in with the template strand, and that is how it knows what nucleotides replace the RNA primer in this molecule. 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 this a little bit later, but the enzyme that replaces or converts the RNA to DNA is going to be DNA polymerase I, a different DNA polymerase. We'll talk more about that later in our course. But for now, this here 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 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.