Microbial Genetics

1. Microbial Genetics

2. Terminology • Genetics • Study of what genes are • how they carry information • how information is expressed • how genes are replicated • Gene • Segment of DNA that encodes a functional product, usually a protein

3. Terminology • Genome • All of the genetic material in a cell • Genomics • Molecular study of genomes • Genotype • Genes of an organism • Phenotype • Expression of the genes

4. E. coli Figure 8.1a

5. DNA • Polymer of nucleotides: adenine, thymine, cytosine, guanine • Double helix associated with proteins • "Backbone" is deoxyribose-phosphate • Strands held together by hydrogen bonds between AT and CG • Strands are antiparallel Figure 8.4

6. DNA Figure 8.3

7. DNA Figure 8.5

8. DNA • DNA is copied by DNA polymerase • In the 5 3 direction • Initiated by an RNA primer • Leading strand synthesized continuously • Lagging strand synthesized discontinuously • Okazaki fragments • RNA primers are removed and Okazaki fragments joined by a DNA polymerase and DNA ligase

9. DNA Figure 8.6

10. DNA • DNA replication is semiconservative Figure 8.7

11. Figure 8.8

12. RNA processing in Eukaryotes Figure 8.12

13. Translation • mRNA is translated in codons (3 nucleotides) • Translation of mRNA begins at the start codon: AUG • Translation ends at a STOP codon: UAA, UAG, UGA Figure 8.2

14. The Genetic Code Figure 8.9

15. Translation Figure 8.10.1

16. Translation Figure 8.10.2

17. Translation Figure 8.10.3

18. Translation Figure 8.10.4

19. Translation Figure 8.10.5

20. Translation Figure 8.10.6

21. Translation Figure 8.10.7

22. Translation Figure 8.10.8

23. Translation Figure 8.11

24. 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

25. Mutation • Change in one baseResult in change in amino acid • Base substitution (point mutation) • Missense mutation Figure 8.17a, b

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

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

28. Mutagen • Ionizing radiation • formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone. • Nucleotide excision repairs mutations

29. Mutagen • UV radiation causes thymine dimers • Light-repair separates thymine dimers Figure 8.20

30. 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

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

32. Replica Plating Figure 8.21

33. The Ames Test for Chemical Carcinogens Figure 8.22

34. 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

35. Transformation Figure 8.24

36. Recombination Figure 8.25

37. Conjugation Figure 8.27a

38. Conjugation Figure 8.27b

39. Conjugation Figure 8.27c

40. Plasmids Figure 8.29

41. 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

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

43. Repression Figure 8.13

44. Operon Figure 8.14.1

45. Regulation of Gene Expression Figure 8.14.2

46. Regulation of Gene Expression Figure 8.14.3

47. Regulation of Gene Expression Figure 8.14.4

48. Regulation of Gene Expression Figure 8.14.5

49. Regulation of Gene Expression Figure 8.15