In this video, we're going to talk about some of the scientists that help with discovering the structure of DNA. Way back in the early 1950s, a female scientist named Rosalind Franklin actually used a technique called x-ray diffraction on DNA, and she used x-ray diffraction on DNA to capture an incredibly important photo that is well known as photo 51. If we take a look at our image down below over here on the left-hand side, you can see an image of the scientist Rosalind Franklin, and you can also see an image of Franklin's photo 51, which again is showing an x-ray diffraction pattern of DNA. What you'll notice is in this x-ray diffraction pattern, these bands create a kind of X-like formation. Through very complicated concepts and math, it turns out that photo 51 here is actually evidence to show that DNA has a double helix structure. However, it wasn't until 1953 that the scientists James Watson and Francis Crick actually were able to use Franklin's photo 51 along with other information that they knew to help them describe the structure of DNA as a double helix structure with 2 antiparallel strands of nucleotides. This is information that we had already covered in some of our previous lesson videos when we first introduced DNA. If you don't remember the information from those older videos on DNA, be sure to go back and check out those older videos on DNA. Watson and Crick had also come up with how these base pairing rules apply, known as Watson and Crick base pairing. Watson and Crick base pairing basically describes how nucleotides on opposite strands of DNA will pair with each other via hydrogen bonds, where all of the adenines or A's would base pair with all of the thymines or T's on opposite strands, and all of the cytosines would base pair and hydrogen bond with all of the guanines on opposite strands. So C's base pair with G's. This is going to be really important information for you guys to be able to keep in mind how the base pairing works, A's with T's and C's with G's. If we take a look at our image down below, over here on the right-hand side, we're showing you the images of James Watson and Francis Crick, who again were able to use Rosalind Franklin's photo 51 along with other information that they knew to help reveal the structure of DNA as a double helix structure where there are 2 strands of nucleotides that are antiparallel with respect to each other. Recall from our previous lesson videos when we first introduced DNA that antiparallel is just referring to the fact that one strand will go from 5 prime to 3 prime in one direction from left to right here, whereas the other strand would go from 5 prime to 3 prime in the opposite direction, and that's why they're called antiparallel. This image over here is showing you how the Watson and Crick base pairing works, where all of the cytosines or C's base pair with all the guanines or G's, and all of the adenines or A's base pair with all of the thymines or T's on opposite strands. And this blue backbone that you see here of the molecule represents a sugar phosphate backbone. We'll get to talk a little bit more about the details of the DNA structure in our next lesson video. But for now, this here concludes our introduction to how the DNA structure was discovered, and we'll be able to get some practice as we move forward in our course. So I'll see you all in our next video.