1. Chapter 8, part C
Microbial Genetics

2. Mutation 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

3. Mutation Base substitution (point mutation) Missense mutation
Change in one base
Result in change in amino acid
Figure 8.17a, b

4. Mutation
Nonsense mutation
Results in a nonsense codon
Figure 8.17a, c

5. Mutation Frameshift mutation
Insertion or deletion of one or more nucleotide pairs
Figure 8.17a, d

6. 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

7. Mutation UV radiation causes thymine dimers
Light-repair separates thymine dimers
Figure 8.20

8. The Frequency of Mutation
Spontaneous mutation rate = 1 in 109 replicated base pairs or 1 in 106 replicated genes
Mutagens increase to 10–5 or 10–3 per replicated gene

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

10. Replica Plating
Figure 8.21

11. The Ames Test for Chemical Carcinogens
Figure 8.22

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

13. Transformation
Figure 8.24

14. Recombination
Figure 8.25

15. Conjugation
Figure 8.27a

16. Conjugation
Figure 8.27b

17. Conjugation
Figure 8.27c

18. Genetic Recombination
Exchange of genes between two DNA molecules
Crossing over occurs when two chromosomes break and rejoin
Figure 8.23

19. Recipient bacterial DNA
Transduction
Phage protein coat
Bacterial chromosome
Recombinant 1
A phage infects the donor bacterial cell. 2
Phage DNA and proteins are made, and the bacterial chromosome is broken down into pieces.
Bacterial DNA
Donor bacterial DNA
Recipient bacterial DNA
Phage DNA
Recipient cell
Recombinant cell 3
Occasionally during phage assembly, pieces of bacterial DNA are packaged in a phage capsid. Then the donor cell lyses and releases phage particles containing bacterial DNA. 4
A phage carrying bacterial DNA infects a new host cell, the recipient cell. 5
Recombinant can occur, producing a recombinant cell with a genotype different from both the donor and recipient cells.
Figure 8.28

20. 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

21. Plasmids
Figure 8.29

22. 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 8.30a, b