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Mutagens and carcinogens

AP.BIO:
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Created by Ross Firestone.

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  • purple pi purple style avatar for user nathanjames503
    What are some examples of non-mutagenic carcinogens?
    (10 votes)
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  • starky tree style avatar for user Gillian Chance Caudill
    Anyone know if you get the table that tells you what proteins the codons code for in the MCAT or do we actually have to memorize it? Does this even matter?
    (4 votes)
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    • blobby green style avatar for user Nimo.Nour01
      I don't think we memorize this, if a passage refers to this, then they would give a table if necessary. The only codons we should definitely memorize is AUG for the start codon which codes for methionine in prokaryotes and Fmethionine for eukaryotes. Also, the three stop codons we need to know is UGA, UAA, UAG. These stop codons don't code for an amino acid. a trick to help memorize them are: U Go Away, U Are Away, U Are Gone.
      (16 votes)
  • blobby green style avatar for user Josh.Monkey.O
    What are some examples of exogenous mutagens? The teacher said nothing about them.
    (0 votes)
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  • blobby green style avatar for user rajath.rao
    Why would 5BU be incorporated into DNA to replace Uracil? Does he mean RNA? Or does it replace Thymine?
    (2 votes)
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  • starky seedling style avatar for user Jenny Kim
    What are examples of mutagens in our lifestyle?
    (2 votes)
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  • male robot hal style avatar for user Amy Khan
    I am wondering how 5-BU could lead to a mutation since it is a base analogue of uracil. and uracil would be found on a RNA strand and RNA is single stranded.
    (2 votes)
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  • starky ultimate style avatar for user Noah Boyd
    Wait... Doesn't Uracil occasionally do "wobble pairing", so it bonds to A or G? Isn't that how multiple codons can code for a single amino acid?
    (1 vote)
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    • blobby green style avatar for user Emailprovider54
      Correct. But I think its important to understand why its permitted to happen. In a codon, most of the time, the third nucleotide could be anything. Wobble pairing is no different. It happens at the third nucleotide in the codon. Essentially there is not much difference between an A,G,C,I,etc at the third nucleotide in the codon.
      (2 votes)
  • blobby green style avatar for user Sophia Su
    How are exogeneous mutagens different from carcinogens, since they are both from the environment.
    (1 vote)
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  • female robot amelia style avatar for user Gail  Golston
    Overall, the difference between mutagensand carcinogens is that mutagen can actually change the DNA structural form and carcinogens just affect uncontrolled cell divisions making too much of something. Am I right?
    (1 vote)
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  • blobby green style avatar for user Mac MacKay
    You should note that processed meat is a class one carcinogen which is in the same class as tobacco and the other carcinogens he listed.
    (0 votes)
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Video transcript

Voiceover: So, today we're going to talk about mutagens and carcinogens and how they can cause DNA damage, but first I want to review the central dogma of molecular biology and how the genetic information of a cell is stored in the form of DNA, which is then transcribed to form RNA and then translated to generate protein. Now, nucleotides from DNA are transcribed to their complementary forms on RNA, which are then read as codons, or groups of three, to code for specific amino acids in a larger protein. Now, if you mutate one of the nucleotides on DNA, like turn this thymine base into an adenine base, then that will affect the RNA sequence and ultimately the protein that follows. So, we say that mutations are mistakes in a cell's DNA that ultimately lead to abnormal protein production. So, what is a mutagen? Well, a mutagen is any chemical substance or physical event that can cause genetic mutations. Chemical substances, like certain poisons, could be mutagens or physical events, like UV light or different kinds of radiation could also be mutagenic, and we classify mutagens into two different categories. So, let's say we have a person over here. A mutagen could be classified as endogenous, if it comes from inside this person's body, and it's some mutagen that's already found in the organism, but an exogenous mutation is one that comes from outside the affected organism, something that's from the external environment. So, what are some examples of some endogenous mutagens? Well, the most significant endogenous mutagens are what we call reactive oxygen species or ROS, and ROS are naturally occurring metabolites in the human body that are produced by mitochondria during oxidative phosphorylation. So, if we have this guy here, who's about to chow down on a big meal, you can expect that during the metabolism of the meal, his mitochondria will produce a bunch of ROS, like O2 dot minus, which we call superoxide, which is an oxygen molecule with one extra electron, as well as some hydrogen peroxide, which is another ROS that your body can produce. Now, reactive oxygen species, as you may be able to tell by their name, contain oxygen, like both of these examples do, but they're also highly reactive with different cell components, including DNA, and by reacting with DNA, they can actually cause significant damage to a cell's genetic code. One example of this type of damage is the double-strand break, and ROS can actually break a DNA's double helix into two smaller pieces, and you can see why this type of a reaction could cause a mutation, since it quite significantly changes the structure of the cell's DNA. The next type of DNA damage that ROS can cause is base modification, and that's when the nucleic acid bases are changed or swapped around, and that can pretty readily cause point mutations or maybe even other kinds. Now, you may be wondering why would a cell ever make something that could damage itself? Well, it turns out that ROS actually have a couple of beneficial effects on a cell, and cells actually have a couple of ways to make sure that they don't cause damage, but sometimes ROS levels get really high, and cells can't deal with them anymore, and we call this oxidative stress, and antioxidants are something that your doctor might have told you that are good for you, and it turns out that part of what antioxidants do is help make sure that ROS don't damage your DNA. Now, let's look at a couple examples of exogenous mutagens, and there are many different types of exogenous mutagens, but we're really only going to talk about two. Now, intercalators are one example, and one of them is called ethidium bromide, which you may be familiar with if you've ever done a PCR experiment before, and what ethidium bromide will do is it will jump into a DNA double helix and stick itself between the two strands, and when these intercalators intercalate into DNA, they can deform the structure of the DNA and cause some serious problems. Base analogs, like 5-bromouracil, which we also call 5-BU, pretend to be a certain base, but then act differently than that base normally would. So, in the case of 5-BU, it's an analog of uracil and looks a lot like it, but once it's incorporated into DNA, it can shift between two different forms. In its keto-form, it will pair best with adenine. While it's in enol-form, it will pair best with guanine. Now, if you're familiar with organic chemistry, you might know that 5-BU can convert between its keto and enol form through something called a tautomerization reaction, and overall you can see how this base analog might be able to induce mutations in a DNA strand. Now, the last thing we're going to talk about is what a carcinogen is. Now, carcinogens can be mutagens, but not all of them are, but in general, you can say that a carcinogen is something that can lead to cancer, which, if you remember, is when cells in an organism divide uncontrollably and can form big masses of cells, called tumors. Now, some carcinogens will work by making mutations in DNA that lead to cancer, but sometimes they might carry out their effects simply by increasing the rate at which a bunch of cells divide, without actually affecting their DNA, and some examples of carcinogens are tobacco, which come from cigarettes, asbestos, which used to be used as home insulation, and even UV radiation. So, what did we learn? Well, first we learned that mutagens are chemical or physical substances or events that can increase the probability of genetic mutations occurring. And next we learned that carcinogens are things that lead to cancer, and while they can be mutagenic as well, they aren't necessarily mutagenic.