Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings PowerPoint ® Lecture Slide Presentation prepared by Christine L. Case M I C R O B I O L O G Y a n i n t r o d u c t i o n ninth edition TORTORA  FUNKE  CASE Part C 8 Microbial Genetics

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Mutation  A change in the genetic material  Mutations may be neutral, beneficial, or harmful.  Mutagen: Agent that causes mutations  Spontaneous mutations: Occur in the absence of a mutagen

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Base substitution (point mutation) - Change in one base  Can be a missense or nonsense mutation.  Missense mutation - Result in change in amino acid Mutation Figure 8.16a–b

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Nonsense mutation - Results in a nonsense codon Mutation Figure 8.16a, c

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Mutation  Frameshift mutation - Insertion or deletion of one or more nucleotide pairs Figure 8.16a, d

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Mutation  Ionizing radiation (X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Mutation  UV radiation causes thymine dimers.  Light-repair enzymes can sometimes separate thymine dimers. Figure 8.19

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Frequency of Mutation  Spontaneous mutation rate = 1 in 10 9 replicated base pairs or 1 in 10 6 replicated genes  Mutagens increase to 10 –5 to 10 –3 per replicated gene.  10 to 1000 more times likely to occur

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Selection  Positive (direct) selection detects mutant cells because they grow or appear different.  Ex. Looking for penicillin resistance on penicillin containing agar  Negative (indirect) selection detects mutant cells because they do not grow.  Use of replica plating can be used for ID PLAY Animation: Mutations and DNA Repair

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Replica Plating Figure 8.20

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Ames Test for Chemical Carcinogens Figure 8.21