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Chapter 8

Chapter 8. Microbial Genetics. Structure and Function of Genetic Material. Learning Objectives. 8-1 Define genetics, genome, chromosome, gene, genetic code, genotype, phenotype, and genomics. 8-2 Describe how DNA serves as genetic information.

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Chapter 8

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  1. Chapter 8 Microbial Genetics

  2. Structure and Function of Genetic Material Learning Objectives • 8-1 Define genetics, genome, chromosome, gene, genetic code, genotype, phenotype, and genomics. • 8-2 Describe how DNA serves as genetic information. • 8-3 Describe the process of DNA replication. • 8-4 Describe protein synthesis, including transcription, RNA processing, and translation. • 8-5 Compare protein synthesis in prokaryotes and eukaryotes.

  3. Terminology • Genetics: The study of what genes are, how they carry information, how information is expressed, and how genes are replicated • Gene: A segment of DNA that encodes a functional product, usually a protein • Chromosome: Structure containing DNA that physically carries hereditary information; the chromosomes contain the genes • Genome: All the genetic information in a cell

  4. Terminology • Genomics: The molecular study of genomes • Genotype: The genes of an organism • Phenotype: Expression of the genes

  5. E. coli Figure 8.1a

  6. Genetic Map of the Chromosome of E. coli Figure 8.1b

  7. The Flow of Genetic Information Figure 8.2

  8. DNA • Polymer of nucleotides: Adenine, thymine, cytosine, and guanine • Double helix associated with proteins • "Backbone" is deoxyribose-phosphate • Strands are held together by hydrogen bonds between AT and CG • Strands are antiparallel Figure 8.3b

  9. Semiconservative Replication Figure 8.3a

  10. DNA Synthesis Figure 8.4

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

  12. Table 8.1

  13. Table 8.1

  14. DNA Synthesis Figure 8.5

  15. Replication of Bacterial DNA Figure 8.6

  16. Give a clinical application of genomics. 8-1 • Why is the base pairing in DNA important? 8-2 • Describe DNA replication, including the functions of DNA gyrase, DNA ligase, and DNA polymerase. 8-3

  17. Transcription • DNA is transcribed to make RNA (mRNA, tRNA, and rRNA) • Transcription begins when RNA polymerase binds to the promoter sequence • Transcription proceeds in the 5' 3' direction • Transcription stops when it reaches theterminator sequence

  18. Transcription Figure 8.7

  19. The Process of Transcription Figure 8.7

  20. The Process of Transcription ANIMATION Transcription: Overview ANIMATION Transcription: Process Figure 8.7

  21. RNA Processing in Eukaryotes Figure 8.11

  22. Translation • mRNA is translated in codons (three nucleotides) • Translation of mRNA begins at the start codon: AUG • Translation ends at nonsense codons: UAA, UAG, UGA Figure 8.2

  23. The Genetic Code • 64 sense codons on mRNA encode the 20 amino acids • The genetic code is degenerate • tRNA carries the complementary anticodon Figure 8.2

  24. The Genetic Code Figure 8.8

  25. Simultaneous Transcription & Translation Figure 8.10

  26. The Process of Translation Figure 8.9

  27. The Process of Translation Figure 8.9

  28. The Process of Translation Figure 8.9

  29. The Process of Translation Figure 8.9

  30. The Process of Translation Figure 8.9

  31. The Process of Translation Figure 8.9

  32. The Process of Translation Figure 8.9

  33. The Process of Translation Figure 8.9

  34. What is the role of the promoter, terminator, and mRNA in transcription? 8-4 • How does mRNA production in eukaryotes differ from the process in prokaryotes? 8-5

  35. Mutation: Change in the Genetic Material Learning Objectives • 8-8 Classify mutations by type. • 8-9 Define mutagen. • 8-10 Describe two ways mutations can be repaired. • 8-11 Describe the effect of mutagens on the mutation rate. • 8-12 Outline the methods of direct and indirect selection of mutants. • 8-13 Identify the purpose of and outline the procedure for the Ames test.

  36. 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

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

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

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

  40. 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 ANIMATION Mutations: Types

  41. Chemical Mutagens Figure 8.19a

  42. Chemical Mutagens ANIMATION Mutagens Figure 8.19b

  43. Radiation • Ionizing radiation (X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone

  44. Radiation • UV radiation causes thymine dimers Figure 8.20

  45. Repair • Photolyases separate thymine dimers • Nucleotide excision repair ANIMATION Mutations: Repair Figure 8.20

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