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Biology: Genetic Mutation

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About this Lesson

  • Type: Video Tutorial
  • Length: 9:56
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 106 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: Mendelian Genetics and Mutation (36 lessons, $54.45)
Biology: Genetic Mutation (4 lessons, $6.93)

Taught by Professor George Wolfe, this lesson was selected from a broader, comprehensive course, Biology. This course and others are available from Thinkwell, Inc. The full course can be found at http://www.thinkwell.com/student/product/biology. The full course covers evolution, ecology, inorganic and organic chemistry, cell biology, respiration, molecular genetics, photosynthesis, biotechnology, cell reproduction, Mendelian genetics and mutation, population genetics and mutation, animal systems and homeostasis, evolution of life on earth, and plant systems and homeostasis.

George Wolfe brings 30+ years of teaching and curriculum writing experience to Thinkwell Biology. His teaching career started in Zaire, Africa where he taught Biology, Chemistry, Political Economics, and Physical Education in the Peace Corps. Since then, he's taught in the Western NY region, spending the last 20 years in the Rochester City School District where he is the Director of the Loudoun Academy of Science. Besides his teaching career, Mr. Wolfe has also been an Emmy-winning television host, fielding live questions for the PBS/WXXI production of Homework Hotline as well as writing and performing in "Football Physics" segments for the Buffalo Bills and the Discover Channel. His contributions to education have been extensive, serving on multiple advisory boards including the Cornell Institute of Physics Teachers, the Cornell Institute of Biology Teachers and the Harvard-Smithsonian Center for Astrophysics SportSmarts curriculum project. He has authored several publications including "The Nasonia Project", a lab series built around the genetics and behaviors of a parasitic wasp. He has received numerous awards throughout his teaching career including the NSTA Presidential Excellence Award, The National Association of Biology Teachers Outstanding Biology Teacher Award for New York State, The Shell Award for Outstanding Science Educator, and was recently inducted in the National Teaching Hall of Fame.

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A question I often get from my students is when we start talking about genetic mutation and, you know, when you start to realize that there are billions of nucleotides in your DNA - billions of these things and millions of genes how could one - one nucleotide change cause some of the effects we see when we see some of the horrible genetic disorders that are common in humans and, of course, we're not the only ones that have genetic disorders but, the bottom line is, of course, we study human genetic disorders the most in our medical attempts to cure suffering. And so this whole idea of mutation looms very large to anyone who really wants to understand and investigate the idea of human genetic disorder. Well, what is a mutation - a genetic mutation? You know about chromosomal mutations in the sense that mutation means change. And you know about chromosomal change - pieces get translocated, you get mixed up, you put one on another and that's an entire chromosomal translocation. You get pieces of chromosome missing. But genetic mutation is a completely different story.
Let's get generic here. Let's talk about something called "point mutations." And they are called point mutations because they happen at one particular place - one point. And there's a variety of these, but I want to talk to you generically about a disease that's been very highly studied because it affects an enormous number of Americans. And so we know an awful lot about this. And that is the disease called Sickle Cell Anemia, which afflicts 1 and 400 African Americans. Now, you may have heard a little bit about Sickle Cell Anemia in this course previously, but let's just do a talk about it. Sickle Cell Anemia is a disease where the person afflicted with the disorder has red blood cells that are twisted out of shape. Their red blood cells do not smoothly pass through their capillaries, they are anemic in the sense that their hemoglobin doesn't work properly - it's a syndrome and it's pleitropic, which means that it has a lot of ramifications throughout all of your body systems. This is caused by a point mutation. This disorder is caused by the change of a single nucleotid, an inheritable single nucleotid change. In other words, it is a genetic change. Now let's keep that whole concept of what are genes. Genes are made out of DNA. And so therefore, if you change an important piece of DNA - remembering that most of your DNA does not code for proteins, but if we just happen spontaneously to change one nucleotid in our DNA sequence and that change happens to be in a germ cell which is going to give rise to gametes that will be passed on. You know there are other mutations - there are other mutations, for example, if I were to have, you know, have a mutation in my skin cell right here because I happen to expose myself to much to ultra violet radiation or x-rays and I had a mutation there. Well, that particular mutation, at that point, is going to be localized. And that particular mutation is not going to be passed on to my offspring because this is not a gamete - it's not a germ cell, but this one is. And so let's talk about it. How can this possibly happen? Well, you have to either get it from your parents or have it form spontaneously.
Let's talk about one that has clearly been passed on through lines. And I want to talk about Sickle Cell Anemia because what I want to show you is this. Sickle Cell Anemia comes from the hemoglobin molecule, which has hundreds of amino acids in it. And therefore, hundreds of nucleotides. And remember I'm not even talking introns here - remember what introns are? Pieces of DNA that are non-functioning that are cut out after the pre-MRNA transcript is made - that pre-MRNA. I want to look at these three nucleotides right here. Now, you remember that what's going to happen with these three nucleotides is they are going to match, during transcription, they are going to match an MRNA strand. Now notice, you remember the whole idea of templates etc., etc. So we're going to get this MRNA that's going to come along and then this MRNA is going to leave the nucleus and go the cytoplasm. And at the cytoplasm, it is going through a whole series of steps you are going to make a hemoglobin molecule. A normal hemoglobin molecule has at this GAAA code on this will code for glutamic acid. And that's fine. But I want to do a contrast here. Let's take a look at mutant DNA. Now, in mutant DNA look what we've done. What we have done is - there's my normal hemoglobin and there's my mutant. And what have we done? We've simply made one nucleotide change - and, obviously it's a pair but I'm just showing you the coding side of the gene. We've made one nucleotide change. And from CTT this pair has - or literally we have an A there now. Well, let's go back to my MRNA remember this MRNA that came in here and matched the CTT - we're showing it with shapes - shape is everything. As we transcribe our new MRNA, you know, I keep saying the new MRNA comes in there. I know that you guys know enough about transcription to know that it just doesn't come in there. It's made by RNA polymerase - the geophyte, the aophyte, but we don't have a match here. So as this thing is polymerizing the new RNA it's not going to put in the GAA as it polymerizes instead, it's going to put something else in. It's going to polymerize - the RNA polymerites is going to read this A and it's going to make GUA. So, it's going to read down there and now you've just made a new MRNA strand. What does that change? Well, what that changes is the code on. And if you look this up you will realize the MRNA, GUA does not code for glutamic acid instead it codes for valine. And so you're saying you're telling me I can see how the change here affects the MRNA that's made and I can see how the MRNA that's made is going to change the amino acid, but you just told me that hemoglobin had hundreds of amino acids in it. One amino acid is going to make a difference. Well, let's think about it. In normal DNA what was the RNA that we made - what was the amino acid that we made? Well, in the normal one you remember here's the sickle cell we had glutamic acid. And this is the R group for glutamic acid right here.
Let's talk about our groups. Remember that amino acids have a structure and a structure looks something like this. It has a carboxyl group off here and R group and an NH^2 group and a hydrogen. And amino acids differ by their R groups. And this particular R group glutamic acid, you'll notice has a polar end. Now, with the glutamic acid, which is in the normal hemoglobin that means that this portion of the protein would not be repelled by water. In other words, it will be on the outside of the molecule and you will probably get some polar-interactions in there which will attract it to other amino acids. But, valine is a different story. Valine has this R group. Look at the difference. Now we have a completely non-polar situation, which makes it hydrophobic. Which is going to take that hemoglobin molecule and twist it in a different direction because where you're going to find valine you're going to be hydrophobic and twist toward the interior of the molecule, giving your hemoglobin a shape that's different enough that the blood cells that you formed look like this and not your typical red blood cells.
So, what may seem to be a subtle change to you becomes a huge change when it manifests. And so this whole idea of genetic disease and disorder is in how they occur comes right down to the level of the DNA.
Mendelian Genetics and Mutation
Genetic Mutation
Genetic Mutation Page [2 of 2]

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