DNA Double Helix - Video Tutorials & Practice Problems
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1
concept
DNA Double Helix Concept 1
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We can say that the researchers of Franklin Watson and Crick are credited with helping describe the structure of DNA. Here we describe DNA as being a double helix with two anti parallel strands of nucleotides. Now, when we say anti parallel, we mean that the two strands run parallel to each other but with opposite directions. And we're gonna say that the double helix represents a twisted ladder where our phosphate sugar backbone are on the signs and the bases are on the inside. If we take a look here at this image we have here in yellow, highlighted in yellow, a phosphate group, a pentose ring and a nitrogenous space. Remember these three components represent a nucleotide. Now, we know that these three components are the main things that contribute to the structure of a nucleotide. Remember the phosphate itself isn't directly attached to the pentose sugar ring, it's attached to the five prime carbon and that five prime carbon is connected to carbon. Number four of the pentose ring. Here, we're going to say that stringing a bunch of nucleotides together through fossil disaster bonds represents the primary structure of our nucleotides. So we have a primary structure. Here, we can say here that it runs from the five prime end down to the three prime end. But we said it runs anti parallel to the other one. So for the basis to be complementary for each other, this three prime end would sync up with the five prime end of this other primary structure. This five prime end would link up with the three prime end of this primary structure we have in the middle, the nitrogenous spaces forming hydrogen bonds with each other or H bonds. So here we have our primary structures, primary structures running anti parallel to each other connected through hydrogen bonds. We say here that our sugar phosphate backbones are these blue parts. And again, our bases are on the interior. This is how we're able to transition from our anti parallel DNA strands to our DNA ladder. Remember this DNA ladder ver really represents a twisted ladder. So the way we do this is we would rotate the top part to the left and then this bottom part to the right, twisting it that way doing that gives us our DNA double helix. So we can see that it resembles the ladder that we had, but it's twisted right. So this is the structure that Franklin Watson and helped us to discover, right? So just remember when we're talking about DNA, it's basically adding together everything we've learned thus far. What is a nucleotide? What are fossil disaster linkages? What is a primary structure. How do our base pair with one another in a complementary fashion by utilizing this anti parallel designation DNA hat? Remember this helps to create the ladder, which really is a twisted ladder to give us our DNA double helix. So just remember these key facts when it comes to the DNA double helix.
2
example
DNA Double Helix Example 1
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1m
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Here in this example, it says predict the sequence of bases in the DNA structure that is complementary to the DNA structure or strand shown below. Remember running anti parallel this top strand, this is the five prime end and this is the three prime end anti parallel means the other strand runs parallel to it but in the opposite direction. So this three prime N would link up with this five prime men. This five prime end would be next to the three primate. Now we just have to remember our base pairings. Remember this is DNA. So a links up with T and G links up with C. So here we have C so this would have to be G, this is G. So this would have to be C, we have three A. So this would be TT and T here we have AC. So this would be a G again, T, here will be a CNC would be G and G T would be with A and A would be with T. Remember we'd have hydrogen bonds in between them. Remember these make three hydrogen bonds and he only make two and then these make three again, three hydrogen bonds, two, three, three, two and two. So this is how we show the sequence of bases. It didn't ask for us to do hydrogen bonds. I decided to add those. But just remember, this is what we mean when we're talking about anti parallel, when it comes to our two DNA strands and how the bases they form complementary base pairings with one another. A bonds with TG bonds with C.
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Problem
Problem
Which of the following statements is false?
A
The nitrogenous bases extend inward within the double helix.
B
The two polynucleotide strands in the DNA double helix are identical to one another.
C
Hydrogen bonding occurs between the two polynucleotide strands within DNA.
D
The complementary strand of DNA segment of 5’ GCATTCAT 3’ would be 3’ CGTAAGTA 5’.
E
Phosphate groups and sugars form the backbone of the DNA double helix.
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