 The actual contents of this monomer here, they were actually known before we had the full structure of DNA. So the actual contents of each monomer here is that you have a base. And in DNA, it's there are four different ones called AG, C and T. Adenine, Grendine, cytosine, and timing. In RNA, you have a different one. I'll get to that one in a second. And then these ones are connected together. And much of this was known already in the 19th century. So it's very old discoveries. It's just that people didn't know that it carried the genetic material at the time. In the early 20th century, it was discovered that these are actually forming multimmers and they're binding together through these phosphates and forming long chains. And I think this is an important lesson too of how fast science has started to move the last few years. Because again, that here we're talking there were decades between the various steps. And even after Levene, it was another 30-plus years before we got to the structure. So if you look at the detail of the DNA here, we first have the phosphates out there. We then have a sugar base, sorry, a sugar in yellow or ribose. And that one is connected to the base in blue. So the nucleobases sitting up there in blue is the one that discovers that's one of what makes each sequence unit here slightly different from the previous ones. I can magnify that a little bit so that we have the base or the nitrous base or the nuclear base. We call it many different things. That base connected to the sugar, which is a pentose ring. So sometimes you would call that a pentose sugar. Those two together is called the nucleoside. And that's again the unit on the inside of the DNA spiral. Together, with at least the first phosphate here, we tend to call them a nucleotide. Sorry, I can only apologize on behalf of a generation of scientists that we didn't give those more unique names, but I can't fix that for you. You're going to need to learn that by heart and separate a nucleotide from a nucleoside. And surprisingly, much of this was known long before we had the full DNA structure because these are simple small compounds that we can compare to other compounds and examine how they were bound. But going from there to the full DNA structure was a significantly greater challenge.