5 - Bacterial Genetics Flashcards
How does genetic material in bacteria differ from our genetic material?
Usually single, circular chromosome.
DNA NOT compartmentalized, localized in bacterial cytoplasm.
Often contains plasmids in addition to chromosome.
Chromosome condensed by supercoiling.
What is the mechanism of chromosome/plasmid replication and cell division on bacteria?
Single origin, 2nd round of replication can start before the cell divides.
Replicated DNA partitioned into daughter cell, binary fission occurs.
How does transcription and translation differ in prokaryotes compared to eukaryotes?
Genes are encoded within operons (euk don’t have operons), there’s NO introns or exons (no splicing) and there’s only 1 RNA pol (euk have 3 RNA pol).
Transcription/transclation are coupled since there’s not compartments. Ribosome is 70S.
What results from binary fission? How do bacteria generate genetic diversity?
Following binary fission, all daughter cells are clonal; however, clones can undergo mutations that confer resistance and then the cells can survive in an environment that they previously would not have survived in.
How does drug resistance develop?
Replication errors induce mutations into gene.
DNA pol misincorporates nucleotide and does not correct this mistake though proofreading.
Most mutations do not confer a selective advantage.
What is the freq of mutation in bacteria?
~1 mutation per 300 chromosome replications.
10^-6 or -7 mutations per genome per generation.
Besides mutations, how else can bacteria develop resistance?
Vertical transmission to progeny.
Horizontal transmission: exchange of genetic transmission from one cell to another.
Bacteria are promiscuous with their DNA, what does that mean?
The species barrier in bacteria is much less stringent than in eukaryotes.
What benefit does gene exchange allow bacteria?
PRovides then with a mechanism to create genetic diversity. Only need a single organism in a population to survive.
Helps then out-compete or kill other organisms and provides selectrive advantage.
Horizontal gene transfer largely responsible for rapid spread of ____ ____? what is an example?
Antibiotic resistnace.
Vancomycin resistance from VRE to VRSE.
Exchange of genetic material between bacteria occurs with great frequency and efficiency where?
Outside and within a host.
What are three exchangeable genetic elements?
- plasmids
- transposable genetic elements
- Pathogenicity islands
What is of most concern when it comes to genes being exchanged between bacteria?
Genes encoding virulence factors and antibiotic resistance determinants.
What are plasmids? How can they be transferred?
ss or ds DNA molecules that replicate independently.
Single F (fertility) plasmids or multiple copies can be in cells.
Can be 1500 bp to 400,000 bp.
Can be transferred between bacteria via transformation, conjugation, and transduction.
What are transposable genetic elements?
Linear DNA segments can be mobilized from one location to another; Often disrupt genes in recipient following transposition.
Cannot replicate on own. Once transferred element can transpose from one location to another in the DNA. Must be present on a plasmid or chromosome to be maintained and passed to daughters.
Transposable elements possess ___ ____ ____ at their ends. What recognizes these?
Inverted terminal repeats (ITR)
Transposase (tnp) enzyme recognizes ITR and cuts the DNA, allowing transposition of element from one location to another. Tnp regulated by TF called tpnA.
What are the different types of transposabel elements?
Composite transposons that insert between two insertion sequences.
Mu bacteriophage: insertion sequence carried in genome of bacteriophage. This phage can carry element from one cell to another.
What is an example of an insertion sequence in the bacterial genome that regulates production of a virulence determinant?
Phase variation of fibriae production: transposase has undergone a mutation that has it locked in the front (promotor) part of the gene that encodes fimbriae.
Insertion sequence undergoes site-specific inversion resulting in a spontaneous switch between non-fimbriated and fimbriated forms.
What does fimbriae promote the attachment to?
Urinary tract epithelial cell surface.
What are genomic pathogenicity islands? What do they often encode?
Large segments of bacterial genome carried plasmid or by bacteriophage.
Often encode determinants that give bacteria survival advantage within a specific environment.
How do genomic pathogenicity islands differ from the majority of chromosome? How are they acquired? What do they encode?
G + C content differs; Acquired by horizontal gene transfer from another organism.
10,000 bp to 200,000 bp
Can encode adherence factors, invasion genes, iron uptake systems, protein secretion systems, and toxins.
Can genomic pathogenicity islands replicate by themself?
Nah, must transpose onto a replicon (plasmid or chrom) in the recipient to be maintained and passed to daughter cells following replication.
What are the three mechanisms by which plasmids, transposable elements, and pathogenicity islands are transferred between bacteria?
- Transformation: DNA uptake from environment
- Conjugation: direct cell to cell contact (via sex pilus)
- Transduction: mediated by bacteriophage.
What type of bacteria can do transformation? What happens to the DNA before it can be internalized by the recipient? What needs to occur for stable inheritance?
Uptake of DNA from environment. Occurs in gram + and - bacteria.
DNA released from donor following lysis, dsDNA bound by recipient then processed to ss before internalization.
Stable inheritance requires recombination with host chrom.
