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Video transcript

today I'm going to give you a quick introduction into genetic mutations but first let's go over the central dogma of molecular biology which is just the idea that genetic information in a cell is stored in the form of DNA and this DNA is used to generate complementary RNA through a process called transcription that RNA is then used to synthesize a corresponding protein to the process of translation so looking at a quick example our short DNA strand here will be used to generate an RNA strand remember that a pairs with you or T and C pairs with G next our RNA will be used to generate protein through translation and remember that during this process RNA nucleotides are read in groups of three called codons in order to generate corresponding amino acids now just very generally we say that mutations have the effect of making this synthesized protein not turn out quite right so I'm going to give a quick shout-out to sickle-cell disease which is an example of a disease that's caused by a genetic mutation so you may remember that there is a protein in red blood cells called hemoglobin which we can also call HB and hemoglobin is a protein that coordinates two iron ions in order to hold on to oxygen molecules and transport them throughout the body now the mutation that causes sickle cell disease results in a mutated form of hemoglobin called HBS being formed where the S is for the word sickle and the difference between normal hemoglobin and HBS is that one glutamate amino acid residue is being replaced with a valine amino acid residue and this small change results in all of these mutated HBS proteins aggregating together in a red blood cell which makes it very difficult for that red blood cell to transport oxygen effectively now just a side point remember that red blood cells are initially generated from hematopoietic stem cells through a process called hematopoiesis so we're mutations found and how do they come up in the first place let's look at a couple different possible mistakes that could lead to an incorrectly produced protein so first we'll see what happens if a cell makes a mistake during translation and we'll stick with our example of sickle-cell disease from before so let's say that we have this sample piece of DNA with three nucleotides from the gene coding for hemoglobin this DNA is transcribed to form the complementary RNA sequence G a G now that G a G would normally correspond to a glutamate residue during translation but a mistake during translation might lead to a valine residue being translated instead to produce the mutated hemoglobin associated with sickle-cell disease but notice that if a mutation happens during translation the cell will only produce one mutated hemoglobin or HBS for each overall mistake and since cells are making tons and tons of hemoglobin just one mutated protein might not have that big of an effect on the cell so we can say that mistakes during translation probably don't cause mutations like the one associated with sickle-cell disease so next we'll look at mistakes during transcription again we have our CTC piece of DNA which would normally make GHG on RNA but maybe a mistake occurs which leads to the transcription of a GU G instead which would then code for the valine associated with mutated hemoglobin now if this mistake occurred the cell would only make a few mutated hemoglobins for each mistake since an individual strand of messenger RNA will only be translated a couple of times before being degraded so we can say that mistakes during transcription probably don't cause mutations like the one associated with sickle-cell disease finally we'll look at mistakes in the DNA strand if our CTC and DNA is mistakenly turned into a CAC then our corresponding RNA from transcription will be changed and ultimately a valine would be produced instead of a glutamic acid now since a cell's DNA stores all of its genetic information that mistake would lead to all future hemoglobins produced from that gene being mutated so overall we can say that mutations will usually result from mistakes in a cell's DNA and not from the RNA or the protein so where do these types of mutations come from well there are two ways a person can genetic mutation the first is that they inherit it from their parents remember that DNA is passed down from parents to offspring so if we have a mutated father here then there's a good chance that at least one of his kids will inherit that mutated gene the same way that the child might inherit any amount of that parents DNA the other possibility is that the mutation will come on spontaneously which is where a person suddenly gets a mutation in their DNA without their parents having had the same mutation and spontaneous mutations can come from many different sources with just a few examples being from DNA replication errors environmental factors like certain poisons or it's also possible that genetic mutations can come on entirely randomly so what did we learn well first we learn that mutations originate at the DNA level and not at the RNA or protein level but the effects of a mutation like the example we gave a sickle-cell disease are found with problems with the proteins that are ultimately expressed by the mutated DNA now like every rule there are a couple of exceptions to this one but we can say that the effects of the mutation are usually found at the protein level and finally we learned that mutations are either inherited from a parent or come on entirely spontaneously
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