Unit Four Mutations •Any alteration in the base sequence of DNA—Errors can occur during DNA replication. •Most discovered and corrected by proof reading enzymes. •Some still are missed. •Theoretical basis for Natural Selection. Types Of Mutations Point Mutation •The substitution of one base for another. •AAAICGGC→AAACCGGC •TTTAGCCG→TTTGGCCG •Replacing the “T” with a “C” changes the T/A pair to a C/G pair. •The particular change would alter the amino acids for the codon from SER to GLY. •May or may not affect the functioning of the protein. •The effect may be positive; i.e., a change which results in a more efficient protein. Silent Mutation •An alteration of the DNA sequence which does not alter the amino acid sequence. oRemember the codon table there are usually more than one codon for each amino acid. (Same protein produced - mutation has no effect). •AAAGAG→AAAGAA•TTTCTC→TTTCTTFrame Shift Mutation oInsertion or deletion of a DNA base shifts the reading frame for the entire downstream sequence. (Small insertion or deletion). oAlters virtually every codon. (Thymadine dimmers). oResults in a nonfunctional protein. Addition/Deletion oLarge insertion or deletion of DNA results in nonfunctional protein. Somatic Cell Mutation oSomatic cells—Every cell in your body that is not a sex cell (sperm/egg). oThese mutations not passed along to offspring. oResult most often from external damage. oPrecursor to cancer. Germ Cell Mutation oMutation in egg/sperm. oPassed on to offspring. o`Basis for Natural Selection. oWhy does changing the A.A. change the protein? o20 Amino Acids oEach has own unique shape and properties. Janich 106 Assignments 1
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