The DNA double helix can unwind, or denature, at temperatures ...

Question

The DNA double helix can unwind, or denature, at temperatures between 90 °C and 99 °C. Denaturing occurs when H bonds are broken. Which of the following strands of DNA would be expected to denature at a higher temperature? Provide an explanation.

Accepted Answer

All right. Hello everyone. So this question says that DNA can denature or unwind when the hydrogen bonds between its base pairs break, this typically occurs at temperatures between 90 °C and 99 °C, which of the following DNA strands would be expected to denature at a higher temperature. And here we have two strands of DNA to examine. Now, we also have four different answer choices labeled a through D proposing which strand would d nature at a higher temperature and why? That's the case? Now without reading the individual answer, choices, I want to draw your attention to the explanations that are given because notice how the answer choices in their explanation talk about the comparisons between A T bonds and GC bonds specifically, which one is stronger? Now just to go ahead and very quickly clarify, what does it mean when something denatures at a higher temperature? Well, if it denatures at a higher temperature, that means that, that the hydrogen bond itself in this particular case, is going to be more stable because if it's more stable, it requires more energy to break, hence the higher temperature. So now how do we determine stability because as mentioned before, both A T and GC bonds are held by hydrogen bonding. Well, the difference is in the number of H bonds per base pair. For example, right, recall that hydrogen bonds between adenine and thymine are two. So there are two hydrogen bonds between adenine and thymine. We can compare this now to cytosine and guanine which has three hydrogen bonds stabilizing this base pair together. And so that's why we tend to examine more closely the number of GC bonds or CG bonds. As I've written here, when determining the stability of a given DNA strand, because GC bonds have more hydrogen bonds holding them together, they are more stable and therefore require more energy to break. So now, let's examine right, let's examine these individual DNA strands and see how many GC pairs, each one of them has starting off with strand number one, we can see right off the bat that the majority of strand one is composed of a bonds looking specifically at the number of CG bonds, we can see that there are four GC bots and here just to clarify, I'll be using GC and CG bonds interchangeably, but in any case, we have four of those in strain one. Now this is in contrast to strain number two, which has significantly more CS and GS across both strands. So examining that just looking for the number of CG bonds or juicy bonds, we can see that that makes up the majority of the given strand. And so the total count for strand two is actually 12 GC bonds. And so from here, because strand two has more GC bonds than strand one, it is going to delete her at a higher temperature. So now I'm going to eliminate options A and C because they state that it's actually strand one that would d nature at a higher temperature. But now we have established that that's not true. So now the question is, what is the right justification? Well, as mentioned before, strand two has a higher GC content, it has more GC bonds because GC bonds are held together by three hydrogen bonds as opposed to two in an A pair, that means that that bond is held stronger, stronger bonding means it's more stable. And if it's more stable, it requires a higher temperature. In other words, more energy to break. And so from there, our answer is going to be option B in the multiple choice which reads that strand two would denature at a higher temperature because it has more GC pairs which form stronger bonds than A T pairs and there you have it. So with that being said, thank you so very much for watching. And I hope you found this helpful.

The DNA double helix can unwind, or denature, at temperatures between 90 °C and 99 °C. Denaturing occurs when H bonds are broken. Which of the following strands of DNA would be expected to denature at a higher temperature? Provide an explanation.

Key Concepts

DNA Structure

Denaturation

GC Content

Watch next