Mutations

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

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

6. Mutation • Insertion or deletion of one or more nucleotide pairs • Frameshift mutation 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 • Occurs during reproduction, between generations of cells • Transfer of genes between cells of the same generation • Vertical gene transfer • Horizontal gene transfer

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 strand DNA binding protein competence-specific protein Figure 13.17 Streptococcus pneumoniae

22. Transduction Phage protein coat Bacterial chromosome Recombinant Phage DNA and proteins are made, and the bacterial chromosome is broken down into pieces. A phage infects the donor bacterial cell. 1 2 Bacterial DNA Donor bacterial DNA Recipient bacterial DNA Phage DNA Recipient cell Recombinant cell 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. 3 A phage carrying bacterial DNA infects a new host cell, the recipient cell. 4 Recombinant can occur, producing a recombinant cell with a genotype different from both the donor and recipient cells. 5 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