Levene’s nucleotide model

11:14have a phosphate. >> Exactly. And these are the things that make up my nuclean. >> Okay. >> Okay. That's that was sort of the prevailing thing. There's four different types of nucleotides. What he did notice was that there's four different types of bases in DNA. Here we're actually showing five because RNA which is another type of nucleon has another type of nucleotide. But notice the following and this is going to be important later with those nitrogenous bases which is part of the building block of this nucleon. >> Mhm. >> Some of them have a single carbon ring. >> Mhm. >> Those are called the paramedines.

11:54>> Yes. >> And then some of them have a double carbon ring. They're a little bit bigger. Right. They've got a pentagon on a hexagon. Whereas the other guys are just a bunch of hexagons, single hexagons. >> Yes. Yes. Yes. >> Right. Yes. >> And and he noticed that there's these four different types. >> And he had this thing called the tetra nucleotide hypothesis, which is basically that all of DNA is just basically made up of these four types of nucleic acids that are all come in four. And this what you're seeing here is the first ever proposed structure for DNA. >> Okay. >> Okay. He's like these four different things. There's the A, there's the C, there's the T and the G. That's adinine,

12:36guanine, cytosine, and thymine. Those things [clears throat] come together and they create a structure called DNA or nuclean at that point. >> And this is what confers that structural scaffold >> into the nucleus. So this is the very very first proposed structure of DNA. >> Okay. >> Okay. Is just like this box-like structure. >> Yes. with with the four just in a little rectangle. Yes. >> Okay. And he's like, "This is what it is. >> It clearly is not what it is. >> It clearly is not what it is. We know that it's >> We know that now. >> We know that now. But back then, back then, you can imagine like the tools that they have is not at all what the tools that we have, right? There's no X-ray crystalallography. There's no um

13:18genetic sequencing. There's you're dealing with really crude tools compared to what we have today. It's incredible that they were able to make to to get to this intuition and this directionality of what was correct. [snorts] >> Details were a little fuzzy, but it was directionally accurate and tactically wrong. >> Yeah. Yeah. Yeah. Tactically wrong. But but he had already figured out that there's four different types. But because he had this hypothesis that well they're all just like >> conglomerated in this square shape, there's no there's no real way for them to >> be complex. They're just simple. Yeah. >> And life is very complex. >> So, how do you how do you go from the simplicity of that structure into all of

13:58the >> complications? And that's kind of a little >> and so they're like, "Okay, okay. So, this is not this is not what it is, right?" >> Okay, that makes sense. That makes sense. >> Then we get to a Fiser. So, this is in Liverpool University.