March%2012%20Mutations%20Posting

March%2012%20Mutations%20Posting - Effect of mutation in...

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5’…ATCGTA TAC GGACGT…3’ 3’…TAGCAT ATG CCTGCA…5 ..A AC. . ..T TG. . ..TA G.. ..AT C.. ..TA T.. ..AT A.. Codon: UAC AAC UAG UAU Amino acid: Tyr Asn Stop Tyr Mutation - Missense Nonsense Silent name: Protein: Wild type Depends Incomplete Wild type ..TAC. . ..ATG. . Effect of mutation in its coding region on a protein DNA: Cell phenotype: wild type depends on environment wild type template
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Potential effects: 1. Change the shape of the protein. 2. Change the temperature stability of the protein (functions at one temperature (37 o C) but not another (48 o C). This is called a “temperature sensitive” mutation; hs or cs. 3. Change interactions with other proteins. 4. Change location of the protein (membrane to cytoplasmic) 5. If the protein is an enzyme, alter it’s activity (change substrate binding or catalytic activity). Missense mutations in proteins change the amino acid sequence
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E31Q 100% E31K 0 W35S 100 H36N 10 K128T 0 K128M 0 Missense mutations in T7 phage lysozyme : some have a big effect and some don’t. K128 E31 W35 H36 This is ‘real’ data Phenotype: Ability to cut peptidoglycan (Relative to wild type)
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Potential effects: If the mutation is not near the C terminal then this will make the protein non-functional. Nonsense mutations in proteins terminate the amino acid sequence early N C
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Let’s Think about basepair mutations 1 1. In the first step of erroneous replication leading to a mutation, a “mismatch” is generated. See cell 2 in the first generation: The two strands of DNA in this cell have 1 mispaired bp. Cell survives if : a) Error is in non-template strand for transcription. b) Error is in template, but “mutant” protein active. c) Error is in the template strand + “mutant” protein not functional, but cell does not require this protein to be active in given environment.
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Let’s Think about basepair mutations 2 2. It takes 2 generations to stabilize a mutation: the error occurs in the first generation, and is stabilized in second generation. The stabilized mutant DNA is structurally normal, all bases complementarily basepaired…. but… 1 basepair differs from wt. Mutant could be viable or not. Depends on a) Activity of the mutant protein b) Environmental requirements c) Effect on phenotype if in non-coding region
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Let’s Think about basepair mutations 3/4 3. Original wt parental genotype/phenotype is NOT lost in the population when mutation occurs. At the end of 2 generations, the original parent has given rise to 4 progeny cells: 1 is mutant, 3 are still wt. 4. Progeny of mutant cell will inherit the mutation (as long as the mutation is not lethal).
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In these mutations, DNA sequences are added or removed from the DNA. This can happen during replication through “strand slippage” Another common form of mutation: insertion and deletion mutations
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Insertion mechanism: Note repetitive sequence AAAAA….
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This note was uploaded on 11/03/2009 for the course ECON 210 taught by Professor James during the Spring '09 term at UBC.

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March%2012%20Mutations%20Posting - Effect of mutation in...

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