Microbial Genetics. Chapter 8

Transcription

1 Microbial Genetics Chapter 8

2 Structure and Function of Genetic Material Genome A cell s genetic information Chromosome Structures containing DNA that physically carry hereditary information Gene Segments of DNA that code for functional products Genotype A cell s genetic makeup Phenotype Organism s expressed properties (how it looks)

3 Figure 8.1a

4 Figure 8.1b

5 Genetic Material DNA and RNA 4 bases: A, C, G, and T in DNA U in RNA DNA Nucleus (eukaryotes) Double stranded RNA Cytoplasm Single stranded Base-Pairing A-T (A-U in RNA) G-C

6 The Flow of Genetic Information DNA Replication Relax supercoil and unwind Helicase Transcribe DNA based on opposite strand Bases added with the enzyme DNA polymerase Semi-conservative replication Parental DNA strand is retained

7 Figure 8.2

8 Figure Overview

9 Figure 8.4

10 The Flow of Genetic Information DNA Replication Bases added in only ONE direction 5 to 3 At Replication fork this gives: Leading strand INTO the fork Lagging strand AWAY from the fork Replication cannot begin de novo Short DNA primers used to start replication DNA pieces (Okazaki Fragments) must be joined together

11 Figure 8.5

12 Figure Overview

13 RNA and Protein Synthesis Transcription mrna codes for proteins or functional RNA Copied directly from DNA template Also 5 to 3 synthesis Made by RNA polymerase Have promoters and terminators

14 Figure 8.7 (Overview) (1 of 7)

15 RNA and Protein Synthesis Translation Convert genetic code from RNA to protein Triplet codons 64 different combinations Degeneracy allows for some errors Code for 20 amino acids and 3 stops AUG codes for both an amino acid (methionine) and the start

16 Figure 8.8

17 Figure Overview

18 Figure Overview (1 of 4)

19 Introns and Exons Introns (rarely found in prokaryotes) Intervening sequence that does not code for proteins Needs to be spliced out before gene is translated Exons are the actual coding sequence Allow organisms to shuffle useful protein motifs Invaluable for evolution Once introns removed the exons are spliced together to make a mature mrna

20 Figure 8. 11

21 Regulation of Gene Expression Cells need to control when and where genes are on Three ways to regulate gene expression Constitutive Repression Induction Regulatory unit called operon

22 Figure Overview

23 Figure Overview

24 Figure Overview

25 Mutations Base substitutions (point mutations) Frameshift mutations (indels) Both lead to three types of end result Silent mutation Mis-sense mutation Non-sense mutation

26 Figure Overview

27 Figure Overview

28 Mutagens Chemical DNA damaging agents (nitrous acid) Nucleoside analogs Anti-viral and Anti-tumor AZT Radiation X-ray and Gamma ray UV light T-T dimers

29 Figure Overview (1 of 3)

30 Figure Overview

31 Figure Overview

32 Selection Positive (direct) Looking for something to grow Makes life easier Negative (indirect) Need to grow on normal media first Replica plate to selective media

33 Figure Overview

34 Identification of Chemical Carcinogens Ames testing -histidine mutant of Salmonella Add suspected carcinogen Look for revertants that can grow on His media

35 Figure Overview (1 of 3)

36 Crossing over Genetic Transfer and Recombination Mixing two homologous DNA sequences Salmonella flagella proteins Vertical transfer From parent to offspring Horizontal transfer From donor to recipient

37 Figure 8.22

38 Bacterial Transformation Bacteria can take up foreign DNA Griffith s experiment with encapsulated Streptococcus pneumoniae

39 Figure Overview

40 Figure Overview

41 Bacterial Conjugation Bacterial sex Uses Pili F+ cells carry a plasmid that they can transfer to F- cells Used to transfer genes to other bacteria

42 Figure 8.25

43 Figure Oveview

44 Bacterial Transduction Carried out by Bacteriophage (phage) Phage chop up host DNA Some host DNA incorporated into phage New phage particle transfers this to new host Specialized transduction Only certain genes transferred C. diptheriae = diptheria toxin S. pyogenes = erythrogenic toxin E. coli O157:H7 = Shiga toxin

45 Figure Overview

46 Plasmids Small, circular DNA molecules Self-replicating Carry genes Catabolize certain sugars Toxins E. coli traveler s diarrhea S. aureus exfoliation toxin C. tetani neurotoxin Resistance factors Antibiotic resistance (Bla)

47 Figure Overview

48 Transposons Mobile DNA Can move about the genome and insert semirandomly If land inside a gene, can cause mutation May carry genes encoding toxins or resistance VRSA Enterococcus faecalis transfer vancomycin resistance to S. aureus (Tn1546)

49 Figure Overview

50 UN 8.1

51 Figure Overview

52 Table 8.1