Term
| what is a genome? what does the bacterial genome consist of? |
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Definition
| the total genetic material found in an organism. the bacterial genome consists of a chromosome, plasmids, bacteriophages, and transposons |
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Term
| what does the bacterial chromosome look like? is it diploid or haploid? are there introns? |
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Definition
| it is a single, circular, dsDNA, highly folded in the cell and encodes 2-4000 genes. it is basically haploid and contains no introns. |
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Term
| what are plasmids? how many are there in a cell? how do they replicate? are they found in gram -/+ bacteria? |
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Definition
| plasmids are small, circular supercoiled DNA. there are 1-5 large plasmid copies in a cell and 10-20 small. they replicate independently of the chromosome, (but can integrate into the chromosome, episome). plasmids are mostly found in gram - bacteria. |
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Term
| what are conjugative/nonconjugative plasmids? |
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Definition
| conjugative plasmids encode transfer enzymes and sex pili for transfer to other cells, (even other species of bacteria). non conjugative plasmids lack transfer genes, but can transfer if in a cell with conjugative plasmid. |
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Term
| what is the medical importance of plasmids? can resistance to more than one kind of antibiotic be transferred at once? |
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Definition
| plasmids can be responsible for transmission of multiple antibiotic resistance or genes for adhesins/toxins/other virulence factors that help bacteria cause disease. resistance to more than one kind of antibiotic can be transferred at once via plasmids. |
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Term
| what are bacteriophages? what is their structure? what kind of genetic material do they have? |
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Definition
| specific viruses that infect specific bacteria. the capsid is icosahedral/helical or both protein subunits that may have a tail and base, but no membrane envelope. the genome can be DNA or RNA, single or double stranded, linear or circular |
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Term
| what are the 2 kinds of bacteriophage lifecycles? |
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Definition
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Term
| what happens in the lytic, (virulent), bacteriophage lifecycle? |
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Definition
| after binding, rapid replication, and within 20 min, lysis. results in cell death and production of a new phage. |
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Term
| what happens in the lysogenic, (temperate), bacteriophage lifecycle? what is a lysogen? lysogenic conversion? |
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Definition
| infection leads to cell lysis or integration of phage DNA into the chromosome, (prophage). a lysogenic conversion is the change of a bacteria into lysogen, which is a bacteria with a prophage. lysogens may aquire antibiotic resistance or some other change through this conversion |
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Term
| can lysogens undergo lysis later? |
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Definition
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Term
| can bacteriophages transfer DNA from other bacteria it has already infected to new, completely different bacteria? |
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Definition
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Term
| what syndrome is associated with streptococcuc pyogenes if infected by bacteriophages? |
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Definition
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Term
| what are the two ways for bacteria to get new genes? |
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Definition
| horizonal gene transfer, (from other like organisms), or from spontaneous mutations, (vertical transfer) |
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Term
| what is bacterial conjugation? |
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Definition
| transfer of DNA from a donor cell to a recipient cell by a conjugative plasmid, (also called F-plasmid for fertility). this requires that the plasmid copies itself followed by intimate contact mediated by sex pili |
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Term
| what is the "tra" gene? where is it found? what does it encode? |
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Definition
| found on f-plasmids, the tra,(transfer) gene encodes sex pili, (F pilus), and special replication enzymes. the pili mediates contact where the cells are drawn together and fuse at a point through which donor DNA is passed. the replication is rolling circle replication so that the donor maintains its copy. |
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Term
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Definition
| resistance plasmid, (F-plasmid harboring an antibiotic resistance gene) |
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Term
| what is an R determinant? |
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Definition
| resistance determinant, a transposon that has an antibiotic resistance gene |
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Term
| what is transduction? does it involve a lysogenic phase? |
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Definition
| transfer of genetic information from one bacterium to another by a bacteriophage. it does involve a lysogenic phase. |
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Term
| what is transformation? do bacteria do this naturally? |
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Definition
| naked DNA from dead bacteria taken in by living cells that incorporate it into their own genome, (if they don't like it they can get rid of it via restriction modification systems). some species of bacteria can do this naturally, if they can, they are referred to as "competent" |
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Term
| what is a complication medically due to bacterial gene transfer? |
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Definition
| if a pt is coinfected with vancomycin resistant enterococcus, (VRE), and methicillin resistant staphylococcus aureus, (MRSA), then the two can both gain dual resistance to both methicillin and vancomycin |
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Term
| what is the difference between homologous and non-homologous recombination? |
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Definition
| homologus recombination occurs between closely related DNA sequences, substitutes one for another. non-homologous recombination occurs between dissimilar DNA sequences and produces insertions, deletions, or both, (used by transposons and lysogenic bacteriophage) |
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Term
| what is a base substitution? transition? transversion? what kinds of mutations might result? what is the clinical significance? |
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Definition
| base substitutions can occur spontaneously due to infidelity of DNA polymerase/chemical instability of bases. an example of a transition would be a purine replaced by a purine, or pyrimidine is replaced by a pyrimidine. transversions are where purines are replaced by pyrimidines or vica versa. these can result in silent, missense or nonsense mutations which could result in antibiotic resistance |
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Term
| what is a frame shift mutation? how does this happen? what is the clinical significance? |
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Definition
| a frame shift mutation is where a single base pair or string of bases, (not in mult of 3), are added or deleted. this occurs in regions containing contiguous short repeats that cause the DNA to stutter and make mistakes, leading to amplification or deletion of a given # of repeats. this can lead to changes on phenotypic surface expression, some cells that have a particular protein/others that don't. the ones that don't might not have infectious ability, but they can establish a colony. |
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Term
| what is a gene rearrangement/inversion? is this reversible? |
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Definition
| a string of bases, (TATA box), is deleted then reinserted in the opposite direction, leading to the DNA being read the opposite way. this is reversible and happens often |
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Term
| what can frameshift mutations and genetic rearrangements, (inversions), result in? |
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Definition
| the ability of the organism to change composition of their surface components to evade the host immune system, (for example antigenic or phase variation) |
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Term
| what is antigenic variation? is LPS subject to this? |
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Definition
| antigenic variation is expression of different variants of a surface molecule. LPS is subject to this |
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Term
| what is phase variation? is LPS subject to this? |
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Definition
| the random presence or absence of a surface molecule. LPS is not subject to this, (b/c it is a part of the cell wall). |
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Term
| what is a transposon? what enzymes control it? can it jump to a plasmid? |
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Definition
| a mobile genetic element that can move from place to place in the chromosome, leaving a copy of itself at the previous site. transposase and resolvase contol its movements. transposons can jump to a plasmid |
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Term
| what is an insertion sequence, (IS)? |
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Definition
| the simplest of the transposable elements, IS is DNA capable of replicating itself into a new site in the chromosome, (or genome), by site-specific recombination, it doesn't really have any other genes |
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Term
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Definition
| an IS element that flanks a structural gene, and carry it to new genome sites/other organisms. |
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Term
| what are pathogenicity islands? |
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Definition
| PAIs are groups of genes that encode for virulence properties, surrounded by transposon-like elements |
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Term
| what are conjugative transposons? |
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Definition
| transposons that mediate transfer through a plasmid-like intermediate |
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Term
| do some transposons have promoters? |
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Definition
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Term
| do bacteria control their genes at the translational or transcriptional level? |
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Definition
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Term
| how do bacteria respond to their environment in response to environmental signals like carbon sources, oxygen, iron, temp, pH, etc? |
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Definition
| bacteria can quickly modulate gene expression in response to environmental signals |
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Term
| how are many genes organized in bacteria? what is mRNA called that comes from these? does this happen in eukaryotic cells? |
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Definition
| as operons, or genes under control of same promoter and termination sequence. mRNA from operons is called "polycistronic" b/c there is more than one gene per mRNA, but the expression can still be individual proteins, (more efficient). this does not happen in eukaryotic cells. |
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Term
| what is an example of an operon in action? |
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Definition
| the e coli lac operon, (genes for enzymes that break down lactose), is repressed in absence of lactose. when lactose is present, it binds to the repressor, which undergoes an allosteric change and binds to the operator. these cells prefer glucose however, so if glucose is available, the lac operon will remain repressed |
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