lect12

lect12 - 1 Mutations and the code Frameshift mutations A...

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Unformatted text preview: 1 Mutations and the code Frameshift mutations A single base-pair deletion or insertion results in a change in the reading frame AUG UUU AG C UUU AGC UUU AGC WT Met Phe Ser Phe Ser Phe Ser Delete C AUG UUU AGU UUA GCU UUA GC Met Phe Ser Leu Ala Leu Insert C AUG UUU AGC C UU UAG CUU UAG C Met Phe Ser Leu STOP 2 Frameshift mutations- Deletion A single base-pair deletion or insertion results in a change in the reading frame AUG UUU AGC UUU AGC UUU AGC Met Phe Ser Phe Ser Phe Ser Delete C Delete GC Delete AGC 3 Frameshift mutations-Insertion A single base-pair deletion or insertion results in a change in the reading frame AUG UUU AGC UUU AGC UUU AGC Met Phe Ser Phe Ser Phe Ser Insert C Insert CC Insert CCC 4 Missense mutations Missense mutations alters ONE codon so that it encodes a different amino acid UUU UUU UG C UUU UUU WT UUU UUU UG G UUU UUU mut 5 Consequences of Missense Mutations Missense mutations alter one of the many amino acids that make a protein Its consequences depend on which amino acid is altered Conservative mutations: K to R Nonconservative mutations: K to E Surface Vs buried Mutations in globular domains Vs un structured tails Silent mutations Mutations in non-coding regions Nonsense mutations 6 Silent Mutations Silent mutations do not alter the amino acid sequence! AUG UUU AGC UUU AGC UUU AGC WT AUG UU C AGC UUU AGC UUU AGC Mut Mutations that occur in introns are also silent Mutations that occur in non-genic regions are silent 7 Mutations in non-protein coding regions Mutations in the promoter or ribosome binding site are also mutagenic Reduced expression of mRNA might result in reduced levels of proteins Mutations in splicing junctions may also be mutagenic Improperly spliced mRNA will result in the intron being Translated Mutations in tRNA or aminoacyl-tRNA synthase are mutagenic 8 Nonsense mutations Nonsense mutations alter one codon so that it now encodes for a STOP codon UUU UUU UGC UUU UUU Phe Phe Cys Phe Phe UUU UUU UGA UUU UUU Phe Phe STOP Nonsense mutations insert a stop codon which results in premature termination Truncated polypeptide usually results in loss of function for polypeptide 9 Nonsense suppressor mutations! These are the result of a mutation in the anti-codon loop of a specific tRNA It allows the tRNA to recognize a nonsense codon and base pair with it. DNA Gene encoding tRNA TRP Point mutation occurs in the anticodon loop This allows this tRNA to base pair with a stop codon and ? 10--- UUU UUU UAG UUU UUU -------- Phe Phe STOP 5--- UUU UUU UAG UUU UUU -----3 AUC Trp AAA Met Ala Phe Phe--- Phe Phe Trp Phe Phe ----> A mutant protein that is larger than normal will be synthesized!! Trp-tRNA has mutation In anticodon This allows it to pair with a stop codon Nonsense suppressor 11 Nonsense and Nonsense suppressor--- UUU UUU CAG UUU UUU -------- Phe Phe Gln Phe Phe ------ UUU UUU UAG UUU UUU -------- Phe Phe STOP Nonsense mutation What will happen if an individual carries both a nonsense mutation in a gene...
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lect12 - 1 Mutations and the code Frameshift mutations A...

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