Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Translation  mRNA is translated in codons (three nucleotides)  Translation of mRNA begins at the start codon: AUG  Translation ends at a stop codon: UAA, UAG, UGA PLAY Animation: Translation Figure 8.2

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Translation Figure 8.10

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Translation Figure 8.9, step 1

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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Translation Figure 8.9, step 8

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Bacterial Gene Expression  Constitutive enzymes are expressed at a fixed rate.  Other enzymes are expressed only as needed.  Repressible enzymes  Inducible enzymes

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Operon PLAY Animation: Operons Figure 8.12, step 1

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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Gene Expression Figure 8.13

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Mutations  A change in the DNA - 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  Mutation  Base substitution (point mutation)  Missense mutation  Change in one base  Result in change in amino acid

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

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

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.  Nucleotide excision repairs mutations.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Mutation  UV radiation causes thymine dimers.  Light-repair separates thymine dimers.

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 or 10 –3 per replicated gene.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Selection  Positive (direct) selection detects mutant cells because they grow or appear different.  Negative (indirect) selection detects mutant cells because they do not grow.

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

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