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Transcript
Bio H – Molecular Genetics Mistakes Happen!! What do we already know about mutations? 1. What are they and what might cause them to form? 2. Are they good? Bad? Neutral? All of the above? Explain citing specific examples with which you are familiar. 3. Think back to our “cooking” analogy with DNA, RNA and protein. How do mutations fit into this analogy and what would the result be? What Categories of Mutations Are There? (you are responsible for all of these) - The below are categories. Depending on what the change is, a mutation might fit into multiple categories at the same time. Point Mutation A point mutation: any mutation in which one base of the gene sequence is changed. A single base can be inserted, deleted or substituted. (you may see it used synonymously with just substitution, but the official definition is broader) Example: Typing the word “Mog” or “Doog” when you wanted to type “Dog”. Frame-shift mutation Any mutation in which one or more base is inserted or deleted. It is the equivalent of adding or removing letters in a sentence. However since the RNA sequence is read three letters at a time, adding or removing one letter changes those groups of three, called the reading frame. That means, that each codon following the mutation is going to be read differently. Example: A sentence like “thecatatetherat” is broken up into a specific reading frame and read as “The cat ate the rat.” But let’s delete the “h” in the first word. This sentence becomes “Tec ata tet her at”. Each letter shifts over one and the sentence makes no sense. If, however, we insert or delete 3 nucleotides (or 6, or 9) then we don’t shift the reading frame, we just add amino acids to our protein. This could still have dire consequences. (ex: The Bad Cat ate the rat) Bio H – Molecular Genetics Other types of Mutations: - Nonsense Mutation: Any mutation that creates a stop codon earlier in the coding sequence than it is supposed to be. This causes the protein to end before it should. This protein will end up shortened, or truncated. This is called a nonsense mutation. - Silent Mutation: If a point mutation changes a codon to another codon that codes the same amino acid, then it will have no effect on the protein. This is called a silent mutation. What do mutations do to proteins? 1. For each type of mutation NEATLY put a line through the part of the original DNA sequence that you are mutating and replace the original sequence with your mutation. 2. NEATLY change the RNA to correspond to your mutated DNA 3. Write in the new Amino Acid sequence that is coded by your mutated DNA. You only need to rewrite the part(s) of the sequences that are affected by the mutation. 1. Substitution – In the sequence below, create a substitution mutation. Replace one nucleotide in the DNA with a different nucleotide Original DNA RNA Transcript: Original Amino Acids GCT ATG CTC GAT CCC TCG ATT CGA UAC GAG CUA GGG AGC UAA Arg Tyr Glu Leu Gly Ser STOP New Amino Acids 2. Deletion – Now create a single nucleotide deletion in the second codon of the DNA sequence. Original DNA RNA Transcript: Original Amino Acids GCT ATG CTC GAT CCC TCG ATT CGA UAC GAG CUA GGG AGC UAA Arg Tyr Glu Leu Gly Ser STOP New Amino Acids 3. Insertion – Now create a single nucleotide insertion in the first codon of your DNA. Original DNA RNA Transcript: Original Amino Acids New Amino Acids GCT ATG CTC GAT CCC TCG ATT CGA UAC GAG CUA GGG AGC UAA Arg Tyr Glu Leu Gly Ser STOP Bio H – Molecular Genetics 4. Silent Mutations – time for a silent mutation. You’ll need to think about this one a little. Remember, what ever change you make, it must still code for the same amino acid. Start by looking at the codon charts to see which amino acids have multiple codons. Original DNA RNA Transcript: Original Amino Acids GCT ATG CTC GAT CCC TCG ATT CGA UAC GAG CUA GGG AGC UAA Arg Tyr Glu Leu Gly Ser STOP New Amino Acids 5. Nonsense Mutations – last but not least, create a mutation in this sequence that changes the third codon in the DNA into a stop codon. Original DNA RNA Transcript: Original Amino Acids GCT ATG CTC GAT CCC TCG ATT CGA UAC GAG CUA GGG AGC UAA Arg Tyr Glu Leu Gly Ser STOP New Amino Acids Discussion Questions: 1. Compare the different types of mutations and discuss whether you think one is “worse” than the other. Support your answer with specifics about each type of mutation. 2. Explain the evolutionary benefit to organisms having what is called a “redundant” code, or the fact that there are multiple codons that code for the same amino acid. Bio H – Molecular Genetics 3. The protein that I did my research on is 481 amino acids long. How long is the RNA transcript for that protein? Careful……. 4. Let say that the protein discussed in #3 above had a substitution that caused a nonsense mutation at base number 333. How would the protein produced be different? (provide specifics) 5. If there are multiple reading frames for every gene, how does the ribosome identify which reading frame is correct? What do mutations do to you? Knowing what mutations do to our amino acid sequences is great, but when was the last time you went to the doctor complaining about your proteins being made of the wrong amino acids? Probably (hopefully?) never. For this reason we’re now going to take a look at some specific diseases caused by such mutations and see what specific symptoms they can cause. 1. Go to our resource page and click on “Interactive DNA, RNA and Protein” under “Human Health” click on “Genetic disorders” Click on “single gene disorders” 2. “Claim” a disease from the list by writing it on the board. If your disease is already written on the board, please select one that is not. By the time we are “presenting” you should be able to discuss the following 1. Pronounce your disease correctly () 2. Know what gene/protein cause the disease 3. Identify specific types of mutations that have been associated with the disease and their inheritance pattern 4. Explain how mutations in the protein lead to the symptoms of the disease. 5. What, if anything, can be done to treat/correct the disease? This site is just to get you started, you may venture out to other sites, just keep track of any website from which you pull information and jot it down on your notes.