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.
Discovering the Structure of DNA: Videos & Practice Problems
Rosalind Franklin's x-ray diffraction image, known as Photo 51, was pivotal in revealing the double helix structure of DNA. This structure consists of two antiparallel strands of nucleotides linked by hydrogen bonds, with adenine pairing with thymine and cytosine pairing with guanine. Each nucleotide comprises a phosphate group, a five-carbon sugar, and a nitrogenous base. Understanding the directionality of DNA strands, with free phosphate at the 5' end and hydroxyl at the 3' end, is crucial for grasping DNA replication and function.
Discovering the Structure of DNA
Video transcript
The scientist/s that was/were given credit for first determining the structure of DNA is/are:
The scientist/s that used x-ray diffraction to help reveal the structure of DNA is/are:
Detailed DNA Structure
Video transcript
In this video, we're going to talk a little bit more about the detailed DNA structure. First, it's helpful to recall the information that we covered about DNA in our previous lesson videos where we first introduced DNA. If you don't know anything about DNA structure, then please be sure to go back and check out those older videos on DNA before continuing here. Now that being said, recall from those older videos that DNA actually consists of two strands of nucleotide monomers or these nucleotide building blocks that are repetitively linked together. If you take a look at our image down below, notice that we're showing you three different representations of the DNA molecule. We've got one representation of the DNA molecule over here, another representation of DNA here in the middle, and a third representation of the DNA molecule over here on the right. Previously, in our previous lesson videos, we had shown that DNA forms a double helix where there are two strands, one strand there and another strand here, that are wrapped around each other and twisted upon each other to create a double helix, this twisting ladder type, formation. But if you were to take this DNA, double helix and you were to untwist the DNA double helix so that it's a straight formation, it would look something like what you see here. And then if you were to zoom into this structure, then you would get this image right here, a more detailed view of the DNA molecule. Again, what you would notice is that the DNA molecule consists of these nucleotides that are repetitively linked together. So here is one nucleotide. This is one nucleotide here. This is another nucleotide here. Here is another nucleotide. These nucleotides are just repetitively linked together to create a DNA strand. We have two DNA strands here. We have one DNA strand right here, and then we have a second DNA strand over here. Notice that these two DNA strands are both made up of nucleotides, and they are connected to each other via these hydrogen bonds that form between the nitrogenous bases. Here we can label these dotted lines as hydrogen bonds that form between the two strands and that connect and keep the two strands held together. Recall from our previous lesson videos that a single nucleotide consists of three components: a phosphate group, a 5-carbon sugar, and a nitrogenous base, either adenine, guanine, thymine, or cytosine, abbreviated as A, G, T, or C. Also, again, recall that these two DNA strands are antiparallel with respect to each other, which means that they go in opposite directions in terms of their 5' prime and 3' prime ends. You can see that this strand over here on the left is going from 5' prime to 3' prime, top to bottom. However, this other strand over here on the right is going from 5' prime to 3' prime in the opposite direction from bottom to top. The DNA strands are going to be antiparallel. When you compare the 5' prime end to the 3' prime end, what you'll notice is that at the 5' prime end of each strand is a free phosphate group. At the 3' prime end of each strand is a free hydroxyl group. What you'll note is that when we take a look at the 5' prime end, again over here, there is a free phosphate group or a phosphate group that is not linked to another nucleotide. Whereas this new phosphate group is not free because it's attached here to two nucleotides. But this is a free phosphate group, and notice that both 5' prime ends have a free phosphate group. Then notice, again, at the 3' prime end, you'll have a free hydroxyl group or a free OH group, And, that applies for both, 3' prime ends. What you'll notice is that here comparing the same sides of the two strands, that they are chemically different. One has a free phosphate group, and one has a free hydroxyl group. That's why it's important to keep in mind the directionality of these DNA strands in terms of their 5' prime and 3' prime ends, and that'll be very important as we move forward in our course and talk about DNA replication. What you'll notice here is that the nitrogenous bases are kind of toward the middle of the DNA molecule and on the perimeter of the molecule is the sugar phosphate backbone. They call it the sugar phosphate backbone because it's a repetitive repeat of sugar phosphate, sugar phosphate group, sugar, phosphate group, sugar, phosphate group, and so on. DNA molecules will have a sugar phosphate backbone. That's why we represent that sugar phosphate backbone here, using these blue lines. This here concludes our brief introduction to some of the detailed DNA structure, and we'll be able to get some practice applying these concepts that we've learned as we move forward in our course. So I'll see you all in our next video.
In the polymerization of DNA, a phosphodiester bond is formed between a phosphate group of the nucleotide being added and which of the following atoms or molecules of the last nucleotide in the DNA strand?
Within a double-stranded DNA molecule, adenine (A) forms hydrogen bonds with thymine (T), and cytosine (C) forms hydrogen bonds with guanine (G). What is the significance of the structural arrangement?
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Who were the key scientists involved in discovering the structure of DNA?
The key scientists involved in discovering the structure of DNA were Rosalind Franklin, James Watson, and Francis Crick. Rosalind Franklin used x-ray diffraction to capture Photo 51, which provided crucial evidence of DNA's double helix structure. James Watson and Francis Crick utilized Franklin's Photo 51, along with other data, to describe DNA as a double helix with two antiparallel strands of nucleotides. Their work revealed the base pairing rules, where adenine pairs with thymine and cytosine pairs with guanine, connected by hydrogen bonds.
Created using AIWhat is Photo 51 and why is it important?
Photo 51 is an x-ray diffraction image of DNA taken by Rosalind Franklin in the early 1950s. This image was crucial because it provided the first clear evidence that DNA has a double helix structure. The x-shaped pattern in Photo 51 indicated the helical nature of DNA, which was later used by James Watson and Francis Crick to model the DNA structure accurately. This discovery was pivotal in understanding the molecular basis of genetic information.
Created using AIWhat are the base pairing rules in DNA?
The base pairing rules in DNA, known as Watson and Crick base pairing, describe how nucleotides on opposite strands pair with each other via hydrogen bonds. Adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). These pairs are complementary, meaning A always pairs with T and C always pairs with G. This specific pairing is crucial for the accurate replication and transcription of genetic information.
Created using AIWhat is the significance of the antiparallel nature of DNA strands?
The antiparallel nature of DNA strands means that the two strands run in opposite directions. One strand runs from 5' to 3', while the other runs from 3' to 5'. This orientation is significant because it allows the complementary base pairs to align properly and form hydrogen bonds. It also plays a crucial role in DNA replication, as enzymes like DNA polymerase can only add nucleotides to the 3' end of a growing DNA strand, ensuring accurate and efficient replication.
Created using AIWhat components make up a nucleotide in DNA?
A nucleotide in DNA consists of three components: a phosphate group, a five-carbon sugar (deoxyribose), and a nitrogenous base. The nitrogenous bases in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G). These nucleotides are repetitively linked together to form the DNA strands, with the phosphate and sugar forming the backbone and the nitrogenous bases pairing to hold the two strands together via hydrogen bonds.
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