Lecture 3 (19) Microbial Genetics Flashcards
plasmid
bacterial molecule separate from chromosome that has small circular DNA that’s replicated and tx to daughter cells
can be implemented into chromosome =episome
episome
plasmid into chromosome
chromosome structure of bacteria
circular, large DNA
polycistronic RNA
mRNA has genetic info to translate more than one protein
negative gene regulation in bacteria
have a repressor binding to a promotor not allowing DNA polymerase to bind and transcribe
positive gen regulation
- used when have a promotor and an RNA polymerase that don’t bind with high affinity
- use activator to bind the gene, cause the RNA polymerase to bind promotor and activate transcription
vertical gene transfer vs horizontal gene transfer
vertical- genes passed via replication to progeny
horizontal- genes passed to other bacteria (not progeny) via transformation, conjugation or transduction
why is bacterial evolution so difficult? what sort of mechanisms has it developed to foil this?
- no DNA is acquired at cell division, bacteria are asexual and evolution is SLOW because there are very little mutations at replication
- therefore bacteria have developed horizontal transmission
homologous recombination
- exchange of DNA between two DNA molecules based on homology
- result: DNA is incorporated into chromosome and is passed to daughter cells and become permanent part of genome
transformation
- horizontal gene transfer
- DNA is lysed somehow and releases DNA
- dependent on homology, new bacterial cell can implement it into its DNA and pass that new DNA onto progeny
- DNA is released into environment and NOT protected before it is implemented into second cell
Conjugation
- transfer of DNA from one viable bacteria to another via a sex pilus and using plasmid
- F FACTOR (fertility) is a plasmid in the bacteria that carries genes called a TRA OPERON that encodes components of the sex pilus bridge
- ori T is the origin of transfer where the single strand break occurs for transfer
- INTERACTION IS ONLY BETWEEN A DONOR (F+) AND RECIPIANT (F-)
f FACTOR
tra gene
ori T
f FACTOR- plasmid that has the ability to tx DNA
tra gene- gene in a f factor bacteria that is able to encode a sex pilus t transfer
ori T- where a single strand-break occurs for transfer on the F factor plasmid
Hfr
- a different type of bacterial donor that has the F factor integrated into its chromosome versus using a PLASMID
- behaves the same as a F+ bacteria
describe conjugation via a F+ plasmid
conjugation via an F+ plasmid causes gene tx at sex pilus encoded by tra gene. The DNA strand of F+ breaks at ori T and a single strand is transferred. Ori T first followed by lastly, the tra gene
F- undergoes sex change to F- and transfer is unidirectional
tra gene is the last thing to be transferred in
describe conjugation via a HFr bacteria
- since the F factor is integrated into the chromosome, transfer includes part of the chromosome next to the ori T
- OFTEN, the conjugation doesn’t last long enough to transfer all of the chromosome and genes. therefore you can have homologous gene transfer of some but not all genes and since tran gene is the last to enter, it has a good likelihood that it wont be transferred
- this means that there is a chance that the bacteria getting these genes are not going to undergo a sex change but gets new genes and can interact with another HFr or a H+
transduction
- transfer of bacterial DNA via bacteriophage (bacteria parasite)
what are the two types of phages?
1) Lytic phage- lytic replication UPON ENTRY into bacteria- meaning that phage enters bacteria and hijacks its cellular machinery to replicate and bacteria are lysed
2) TEMPERATE/lysogenic phage- integrates itself into the chromosome of the bacteria and remains dormant until an assault occurs and the bacteria become virulent and lyses the bacteria
describe generalized transduction
- a LYTIC phage injects its DNA into the bacteria
- upon replication, the phage secretes nucleases that degrade the bacteria
- phage is messy about its replication and can actually integrate bacterial chromosomal DNA into its phage head
- when phage infects another bacteria, the DNA can be incorporated into its chromosome via homologous recombination
specialized transduction
- uses temperate/lysogenic phage
- phage incorporates itself into host chromosome and waits
- insult leads to conversion to a lytic lifecycle
- the phage then excises itself from the “sinking ship” of a bacteria and when it does this, it can take some of the bacterial DNA with it
- this can be implemented into other bacteria
what type of bacterial transfer requires homologous recombination
transformation, transduction and conjugation with HFr. F+ and F- conjugation does not need homologous recombination
what type of DNA is used in transformation, conjugation and transduction
transformation- any
conjugation- chromosomal or plasmid
transduction- Generalized is any, specialized is only genes adjacent to phage insertion
what type of transfer process is involved in transformation, conjugation and transduction
transformation- uptake of free DNA
conjugation- cell to cell tx
transduction- phage tx
what are the three types of antibiotic resistance
1) intrinsic
2) chromosome- mediated
3) plasmid-mediated
intrinsic antibiotic resistance
- NOT horizontally transferred by bacteria
- not increasing among bacterial populations
- when a bacteria has some feature, intrinsically that makes them resistant to antibiotics
