113lecture1406

113lecture1406 - BIOLOGY 113 - MICROBIOLOGY Lecture 14:...

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BIOLOGY 113 - MICROBIOLOGY Lecture 14: Microbial Genetics - Types of mutations, mutagenic agents, identifying mutants and mutagens A mutation can be defined simply as a change in the base sequence of a DNA molecule - From our understanding of genetic expression, it can be expected that such a change in DNA base sequence could lead to a change in the amino acid sequence of a cellular protein if the mutation occurs in a structural gene = For example, if a gene for an enzyme is mutated, the change in amino acid sequence could cause the enzyme to become inactive = Of course, in rare instances, a change in the amino acid sequence could lead to an enzyme that allows the organism to function better in its environment; such is the nature of evolution - Many simple mutations are neutral in that they do not actually cause a change in a cell's phenotype = If the DNA base change results in a change from one mRNA codon to another encoding the same amino acid (e.g., GC A to GC G, both of which encode alanine), an identical protein will be produced = Even if there is an amino acid change, not all such changes alter the function of the protein Mutations can be classified according to the nature of the change in DNA base sequence the the resulting effect on a cell's phenotype - The most common type of mutation is a base substitution or point mutation, involving a single base pair (Tortora et al., Figure 8.16) = For example, A=T might be substituted for G C, or C G might be substituted for G C = If the base substitution results in incorporation of a different amino acid in a protein, it is known as a missense mutation (Tortora et al., Figure 8.17(b))) = A base substitution leading to substitution of a stop codon for a codon encoding
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This note was uploaded on 11/24/2011 for the course BIO 113 taught by Professor Staff during the Fall '09 term at Rutgers.

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113lecture1406 - BIOLOGY 113 - MICROBIOLOGY Lecture 14:...

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