14. DNA Synthesis
Discovering the Structure of DNA
1
concept
Discovering the Structure of DNA
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in this video, we're going to talk about some of the scientists that helped with discovering the structure of DNA. And so way back in the early 19 fifties, Ah, 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. And so, 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. And so what you'll notice is in this X ray diffraction pattern. These bands, uh, that create this kind of X like formation, and so through very, very complicated concepts and math. Uh, it turns out that this photo 51 here is actually evidence to show that DNA has a double helix structure. However, it wasn't until the 1953 that the scientists, James Watson and Francis Crick, actually were able to use Franklin's photo along with other information that they knew toe help them describe the structure of DNA. And so they described DNA as a double helix structure with two anti parallel strands of nucleotides. And so, of course, this is information that we had already covered in some of our previous lesson videos when we first introduced DNA. And so, if you don't remember three information from those older videos on DNA, be sure to go back and check out those older videos on DNA. Now Watson and Crick had also come up with how these base pairing rules apply. And so it's known as Watson and Crick base pairing. And so Watson and Crick, basic comparing, basically describes how the nucleotides on opposite strands of DNA will actually pair with each other via hydrogen bonds, where all of the ad innings, or ACE, would base. Pair with all of the thigh means or tease on opposite strains and all of the side of scenes would base pair and hydrogen bond with all of the guanine means on opposite strands. Sow seeds, base pair with GS. And so this is gonna be really important information for you guys to be able to keep in mind how the base pairing works A's with teas and sees with cheese. And so if we take a look at our image down below, of course, over here, on the right hand side, we're showing you the images of James Watson and Francis Crick, who again, we're 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 two strands of nucleotides that air anti parallel with respect to each other and, of course, recall from our previous lesson videos when we first introduced DNA. That anti parallel is just referring to the fact that one strand will go five prime to three prime in one direction from left to right here, whereas the other strand would go five prime to three prime in the opposite direction. And that's why they're called anti parallel. And of course, this image over here is showing you how the Watson Crick base pairing works where all of the site of scenes or sees base pair with all the guanine Zorg es and all of the ad means or ace base pair with all of the thigh means or tease on opposite strains. And this blue backbone that you see here of the molecule represents a sugar phosphate backbone. And we'll get to talk a little bit more about the details off 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.
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Problem
ProblemThe scientist/s that was/were given credit for first determining the structure of DNA is/are:
A
Hershey and Chase.
B
Watson and Crick.
C
Chargaff.
D
Griffith.
E
Hershey and Crick.
F
Watson and Chase.
3
Problem
ProblemThe scientist/s that used x-ray diffraction to help reveal the structure of DNA is/are:
A
Watson and Crick.
B
Hershey and Chase.
C
Avery and Macleod.
D
Chargaff.
E
Franklin.
4
concept
Detailed DNA Structure
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in this video, we're going to talk a little bit more about the detailed DNA structure. And so first, it's helpful to recall the information that we covered about DNA in our previous lesson videos where we first introduced DNA. And so 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 thes nucleotide building blocks that air repetitive Lee linked together. And so, if you take a look at our image down below notice that were actually 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. And so 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 is twisting ladder type formation. But if you were to take this DNA double helix and you were toe untwist the DNA double helix so that it's ah, 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. And again, what you would notice is that the DNA molecule consists of these nucleotides that air repetitive Lee linked together. So here is one nucleotide Uh, this is one nucleotide here. This is another nucleotide here. Here is another nucleotide. And so these nucleotides are just repetitive Lee linked together to create a DNA strand. And so we have to DNA strands. Here we have one DNA strand right here on and then we have a second DNA strand over here. And so notice that these two DNA strands are both made up of nucleotides and they're connected to each other via these hydrogen bonds that form between the nitrogenous basis. And so here we can label these dotted lines as hpe bonds or hydrogen bonds that form between the two strands and that connect and keep the two strands held together. Now recall from our previous lesson videos that a single nucleotide consists of three components. It consists of a phosphate group, a five carbon sugar and a nitrogenous base. Either add ning guanine timing or cytosine abbreviated as a G, T or C, and also again recall that these two DNA strands are anti parallel with respect to each other, which means that they go in opposite directions in terms of their five prime and three prime ends. And so you can see that this strand over here on the left is going from five prime to three prime top to bottom. However, this other strand over here on the right is going from five prime to three prime in the opposite direction from bottom to top. And so the DNA strands are going to be anti parallel. And when you compare the five prime into the three prime end, which you'll notice is that at the five prime in of each Strand is a free phosphate group, and at the three prime end of each strand is a free hydroxyl group. And so what you'll note is that when we take a look at the five 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 to, uh, nucleotides. But this is a free phosphate group and notice that both five prime ends have a free phosphate group and then notice again at the three prime end. You'll have a free hydroxyl group or free O H group, and that applies for both three prime ends. And so what you'll notice is that, uh, 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. And so that's why it's important to keep in mind the directionality of these DNA strands in terms of their five prime and three prime ends. And that will be very important as we move forward in our course and talk about DNA replication. Uh, now what you'll notice here is that, uh, the nitrogenous bases are kind of towards the middle of the DNA molecule, and on the perimeter of the molecule is the sugar phosphate backbone, and 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. And so DNA molecules will have a sugar phosphate backbone. And that's why we represent that sugar phosphate backbone here using these blue lines. And so this here concludes our brief introduction to some of the detail 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.
5
Problem
ProblemIn 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?
A
The 5' phosphate group.
B
C6.
C
The 3' OH.
D
A nitrogen from the nitrogen-containing base.
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Problem
ProblemWithin 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?
A
It allows variable width of the DNA double helix.
B
It permits complementary base pairing.
C
It determines the tertiary structure of the DNA molecule.
D
It determines the type of protein produced from the DNA.
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