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Unit4_notes - Unit Four Mutations Any alteration in the...

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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 AAA C CGGC TTTAGCCG TTT G GCCG 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. o Remember the codon table there are usually more than one codon for each amino acid. (Same protein produced - mutation has no effect). AAAGAG AAAGA A TTTCTC TTTCT T Frame Shift Mutation o Insertion or deletion of a DNA base shifts the reading frame for the entire downstream sequence. (Small insertion or deletion). o Alters virtually every codon. (Thymadine dimmers). o Results in a nonfunctional protein. Addition/Deletion o Large insertion or deletion of DNA results in nonfunctional protein. Somatic Cell Mutation o Somatic cells—Every cell in your body that is not a sex cell (sperm/egg). o These mutations not passed along to offspring. o Result most often from external damage. o Precursor to cancer. Germ Cell Mutation o Mutation in egg/sperm. o Passed on to offspring. o `Basis for Natural Selection. o Why does changing the A.A. change the protein? o 20 Amino Acids o Each has own unique shape and properties. Janich 106 Assignments 1
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