In this video, we're going to talk more details about ribosomes, specifically the ribosome subunits. And so ribosomes, which recall are the main structure responsible for translation, actually consist of 2 subunits or 2 components that are referred to as the small and large ribosomal subunits. And so each of these subunits, the small and large ribosomal subunits, are made of proteins and ribosomal RNA or rRNA. Now it turns out that the ribosomes of prokaryotes differ from the ribosomes of eukaryotes. And so notice down below in our image, we're going to be talking about prokaryotic ribosomes over here on the left-hand side, and on the right-hand side, we're going to be focusing on eukaryotic ribosomes.
Now, again, it's very important to make sure that you're able to distinguish the complete intact ribosome from the other ribosomal subunits that come together. And so, again, what you'll notice here is that there is a large ribosomal subunit and then there is a small ribosomal subunit. And the large and small ribosomal subunit need to come together to form the complete intact ribosome. Okay? And so, that's important to keep in mind.
Now it turns out that prokaryotes, they actually have a complete intact ribosome with both subunits combined, that's referred to as a 70S ribosome. Okay. So the complete intact ribosome for prokaryotes with both subunits combined together is called a 70S ribosome. So we can fill that in down below in our image. Now the 70S ribosome of prokaryotes, again, it's going to be made of these 2 subunits, the large ribosomal subunit and the small ribosomal subunit.
The large ribosomal subunit on its own when it is separate from the small ribosomal subunit is referred to as a 50S large ribosomal subunit. And the small ribosomal subunit of prokaryotes is going to be referred to on its own as a small 30S ribosomal subunit. And so one thing to note here is that 50 + 30 does not equal 70, and that's okay. That is how this works. It is not going to be the sum of these 2 subunits that gives you the complete intact ribosome.
Instead, this s here is a unit that you don't really need to worry about for the purposes of our course, but it is the Svedberg unit. And it basically describes how these ribosomes would, basically, sediment, or centrifuge in a complex process. So you don't need to worry about what this s is. But what you should note one thing that's important to note is that the 50S plus the 30S does not equal 70S, and that's okay. That's how this works.
So prokaryotes have a 70S complete intact ribosome that is made up of a large 50S subunit and a small 30S subunit. Now, eukaryotes on the other hand, which are over here, their ribosomes, as we mentioned, are different. And so eukaryotes actually have an 80S intact ribosome, complete intact ribosome. So when both the large and small subunits are complexed together, the entire ribosome is referred to as an 80S ribosome in eukaryotes. And so, this complete intact 80S ribosome in eukaryotes, of course, is going to be made up of smaller components, the smaller subunits, the large subunit and the small subunit.
And so the large ribosomal subunit in eukaryotes is actually going to be a 60S large ribosomal subunit. And so you can see this, the 60S subunit is this large ribosomal subunit. And the small ribosomal subunit for eukaryotes is going to be a 40S small ribosomal subunit. So you can see the 40S for small ribosomal subunit is here. And so once again, 60 plus 40 does not equal 80, but that's okay.
That's how this process works. And so, the 80S ribosome is composed of the 60S and the 40S subunit. And so, this here is how it works, but how are you supposed to remember this process? How are you supposed to remember that the prokaryotic ribosome is a 70 s ribosome when it's completely intact and that it's made up of a large fifty s ribosomal subunit and small 30 s ribosomal subunit and, also the details of the eukaryote. How are you supposed to remember that?
Well, an easy way that helps me remember this is that, notice that all of these numbers, if you put them together, they're basically, just going 30, 40, 50, 60, 70, 80. 30, 40, 50, 60, 70, 80. So what I like to do is I write down all of those numbers in, their order. So I say 30, 40, 50, and then I say, okay, well, 60, 70, 80. And then what I like to do is I like to put them in pairs.
Okay? And I say, okay, 30, 40 is the pair, 50, 60 is a pair, and 70, 80 is a pair. And so the 30, 40, because those are the smallest numbers, this is going to represent the small ribosomal subunits. And, of course, the 50, 60 is a little bit larger, so this is going to represent the large ribosomal subunits. And then, of course, the 70, 80 over here is going to be representing the complete intact ribosomes, complete intact ribosomes.
And so, of course, the complete intact ribosome is when the small and large ribosomal subunits come together. So now that I've got those pairings there, then I know that the smaller number within each pair is going to be prokaryotic. So I know the 30S is going to be here, the 50S is going to be here, and the 70S is going to be here. And then the larger number in each pair is going to be eukaryotic. So you can see the 40S is here, the 60S is here, and the 80S is here.
And so if you just order these numbers, 30, 40, 50, 60, 70, 80, and do what we talked about here in this video, then you'll have no problem remembering the components and the differences between prokaryotic and eukaryotic ribosomes. And so this here concludes our brief introduction to the ribosomal subunits and we'll continue to talk more about ribosomes and the process of translation as we continue to move forward in our course. So I'll see you all in our next video.