15BIS101F2013MutatLect15

A single base change addition or deletions are

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Unformatted text preview: nes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 21 Molecular Basis of Mutation (Cause and Effect) Molecular Basis of Mutation (How mutations occur) BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 22 Spontaneous Mutations Point Mutations affect only one or two bases in a DNA sequence. A single base change, addition, or deletions are examples of point mutations. Shown below is the effects of point mutations at each of the three positions of the tyrosine codon. three GAU asp CAU his AAU asn UAG non UAU tyr UGU cys UCU ser UAA non UAC tyr UUU phe BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 23 Spontaneous Point Mutations Transition: Mutations that change purines and pyrimidines to their Mutations alternate forms (e.g., A G; C T, etc.). Transversion: Mutations that change purines to pyrimidines and vice Mutations versa (e.g., A C, T G, etc.). Transition A G Transversion Transversion T C Transition BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 24 Tautomeric Shifts (definition) Tautomeric shift (tautomerization): The spontaneous, rare, rapid and reversible isomerization of nitrogenous bases to alternative H-bonding forms (imino/enol forms of pyrimidines and amino/keto forms of purines) due to proton migration around purine rings. Tautomerization creates the possibly of non-canonical base pairing in DNA resulting in mutations or in RNA producing wobble in the anticodon loop of tRNA. BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 25 Tautomeric Shifts in DNA (proton migration) Tautomeric Shifts and Mutations BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 26 Tautomeric Shifts Mispairing of G* to U due to tautomeric shifts. BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 27 Normal Hydrogen Bonding between Bases BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 28 Rare Pyrimidine Tautomeric Shifts Mispairing of C* and T* to A and G bases due to tautomeric Mispairing shifts. shifts. BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 29 Rare Purine Tautomeric Shifts Mispairing of A* and G* to C and T bases due to tautomeric Mispairing shifts. shifts. back mutation BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 30 “Fixing Mutations by 2 R...
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