1. Regulation of Bacterial Gene Expression Constitutive enzymes are expressed at a fixed rate. Other enzymes are expressed only as needed. –Repressible enzymes –Inducible enzymes

2. Operon Figure 8.12, step 1

3. Induction Figure 8.12, step 2a

4. Induction Figure 8.12, step 3a

5. Repression Figure 8.12, step 2b

6. Repression Figure 8.12, step 3b

7. Regulation of Gene Expression Figure 8.13

8. 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

9. Base substitution (point mutation) Missense mutation Mutation Change in one base Result in change in amino acid Figure 8.16a–b

10. Nonsense mutation Mutation Results in a nonsense codon Figure 8.16a, c

11. Mutation Frameshift mutation Insertion or deletion of one or more nucleotide pairs Figure 8.16a, d

12. 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.

13. Mutation UV radiation causes thymine dimers. Light-repair separates thymine dimers. Figure 8.19

14. 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.

15. Selection Positive (direct) selection detects mutant cells because they grow or appear different. Negative (indirect) selection detects mutant cells because they do not grow.

16. Replica Plating Figure 8.20

17. The Ames Test for Chemical Carcinogens Figure 8.21

18. Genetic Transfer and Recombination Vertical gene transfer: Occurs during reproduction between generations of cells. Horizontal gene transfer: The transfer of genes between cells of the same generation.

19. Transformation Figure 8.23

20. Recombination Figure 8.24

21. Conjugation Figure 8.26a

22. Conjugation Figure 8.26b

23. Conjugation Figure 8.26c

24. Transduction Figure 8.27

25. Genetic Recombination Exchange of genes between two DNA molecules –Crossing over occurs when two chromosomes break and rejoin Figure 8.22

26. Plasmids Conjugative plasmid: Carries genes for sex pili and transfer of the plasmid Dissimilation plasmids: Encode enzymes for catabolism of unusual compounds R factors: Encode antibiotic resistance

27. Plasmids Figure 8.28

28. Transposons Segments of DNA that can move from one region of DNA to another. Contain insertion sequences for cutting and resealing DNA (transposase). Complex transposons carry other genes. Figure 8.29a–b

29. Transposons Figure 8.29c