Microbial Genetics Chapter 8
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)
Figure 8.1a
Figure 8.1b
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
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
Figure 8.2
Figure 8.3 - Overview
Figure 8.4
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
Figure 8.5
Figure 8.6 - Overview
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
Figure 8.7 (Overview) (1 of 7)
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
Figure 8.8
Figure 8.9 - Overview
Figure 8.10 - Overview (1 of 4)
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
Figure 8. 11
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
Figure 8.12 - Overview
Figure 8.13 - Overview
Figure 8.14 - Overview
Mutations Base substitutions (point mutations) Frameshift mutations (indels) Both lead to three types of end result Silent mutation Mis-sense mutation Non-sense mutation
Figure 8.15 - Overview
Figure 8.16 - Overview
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
Figure 8.17 - Overview (1 of 3)
Figure 8.18 - Overview
Figure 8.19 - Overview
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
Figure 8.20 - Overview
Identification of Chemical Carcinogens Ames testing -histidine mutant of Salmonella Add suspected carcinogen Look for revertants that can grow on His media
Figure 8.21 - Overview (1 of 3)
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
Figure 8.22
Bacterial Transformation Bacteria can take up foreign DNA Griffith s experiment with encapsulated Streptococcus pneumoniae
Figure 8.23 - Overview
Figure 8.24 - Overview
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
Figure 8.25
Figure 8.26 - Oveview
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
Figure 8.27 - Overview
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)
Figure 8.28 - Overview
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)
Figure 8. 29 - Overview
UN 8.1
Figure 8.1 - Overview
Table 8.1