1. Mutations

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 Mutations Transformation Transduction Conjugation
Jumping Genes

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

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

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

7. 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

8. Mutation UV radiation causes thymine dimers
Light-repair enzymes separates thymine dimers through photoreactivation
SOS repair for extremely damaged DNA (this process is error proned).
Figure 8.20

9. 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

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

11. Induced Mutations
caused by chemical or physical agents that damage or alter the chemistry of DNA, or that interfere with DNA repair mechanisms

14. DNA-damaging agents

15. Replica Plating
Figure 8.21

16. The Ames Test for Chemical Carcinogens
Figure 8.22

17. 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

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

19. Recombination
Figure 8.25

20. Transformation
Figure 8.24

21. Transformation nuclease – nicks and degrades one DNA binding strand
protein
nuclease – nicks and degrades one
strand
Mechanism of transformation in S pneumoniae. A long double stranded DNA binds cell surface with the aid of DNA-binding proteins and is nicked by nuclease. One strand is degraded by nuclease. The undegraded strand associates with a competence-specific protein. The single strand enters the cell and is integrated into the host chromosome at a homologous site in the host DNA.
competence-specific
protein
Figure 13.17
Streptococcus pneumoniae

22. 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

23. Transduction
Figure 13.20

24. Specialized Transduction
also called restricted transduction
carried out only by temperate phages that have established lysogeny
only specific portion of bacterial genome is transferred
occurs when prophage is incorrectly excised

25. Specialized transduction Lysogeny
Figure 13.20

26. Conjugation
Figure 8.27a

27. Conjugation
Figure 8.27b

28. Conjugation
Figure 8.27c

29. 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

30. Plasmids
Figure 8.29

31. 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