Ultraviolet (UV) radiation is mutagenic.
Identify and de...

Question

Ultraviolet (UV) radiation is mutagenic.

Identify and describe two DNA repair mechanisms that remove UV-induced DNA lesions.

Accepted Answer

Hi, everybody. Let's look at our next problem. It says U V radiation can cause a muto GIC impact on an organism's DNA. The DNA repair mechanism in which the strand segment containing the damaged DNA region is removed and replaced by a new DNA segment is called choice. A mismatch repair. B base excision repair, C, nucleotide excision repair and D photo reactive repair. Well, we have two key pieces of information in deciding which repair mechanism we're going to use here. This is a little bit of a deceptively simple question because we're dealing with U V radiation and its mugen impact. And there's kind of two different pathways that can be used for the repair of damage caused by U V radiation. So the key things we're going to want to focus on here are that it's U V radiation, that's the kind of damage that's caused. And that the repair mechanism that was used is one in which the damaged DNA region is removed and replaced. So the two methods of dealing with U V radiation damage are nucleotide excision repair. And we see that as answer choice C here and photo reactive repair, which we see as answer choice. D nucleotide excision repair is used by EOS and photo reactive repair. Uh in general used by bacteria and a few other organisms. But we're not told in our problem whether it's E Caro or pro Caro that it's happening in. However, we are told that the damaged DNA region is removed and replaced and that is going to indicate nucleotide excision repair. And we have even in our name right there, the key word excision cutting out. So that can give you a reminder if you've forgotten photo reactive repair involves the enzyme photo lia and it catalyzes a reaction in which the damage is directly reversed. And this is because the damage that was caused is the formation of pyrimidine diers. So the U V light we can recall can cause covalent bonds to form between two neighboring pyrimidines, most commonly two thymine residues and that can cause a distortion in the DNA double helix. So in the case of photo reactive repair, the photo ice actually catalyzes the breaking of those covalent bonds, restoring the pramine to their original state. So just kind of a direct reversal of the damage in N er nucleotide excision repair, that whole distorted region of the DNA is cut out and replaced with the correct basis. So since our question says the damage DNA is removed and replaced, that leads us to choice C nucleotide excision repair and eliminates choice D photo reactive repair, which as we said was the other method of repairing U V radiation cause damage to be thorough. Let's look at our other answer. Choices. Choice. A mismatch repair would not be correct here because that is, as its name indicates, repair when you just have two bases mismatched. So you have a wrong pairing app, maybe you have an A paired with A G instead of A T and it removes the mismatched base and replaces it with the correct one. But that's not the result of U V radiation and not what we're looking for here. And then finally choice B base excision repair. So this is similar to N er and in fact, it can be tricky to keep the two of them straight. But in the case of base excision repair, what's being excised and replaced is just a single damaged base. So usually when you have some sort of chemical modification done to a single base and that damage base is excised and replaced with the correct one nucleotide excision repair. You are talking about more extensive, we'd say bulky lesions that distort the double helix. So in base excision repair, we don't have that distortion of the structure just damaged to a single base nucleotide excision kicks in when the damage is extensive enough that you've actually um distorted the helix itself. So that's why choice B base excision repair is not a correct answer. So this one looks very simple and straightforward on the top of it and it is in one sense, but it can be a little tricky because keeping straight each of these mechanisms when they occur and what differentiates them from each other can be a little bit tricky. But we've walked through why. In this case, we're looking for choice C nucleotide excision repair. See you in the next video.

Ultraviolet (UV) radiation is mutagenic.
Identify and describe two DNA repair mechanisms that remove UV-induced DNA lesions.

Key Concepts

UV-Induced DNA Lesions

Nucleotide Excision Repair (NER)

Photoreactivation

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