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46 Cards in this Set
- Front
- Back
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What is the prokaryotes equivalent to the eukaryotes nucleus?
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A nucleoid
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Do prokaryotes have histone-like proteins to tightly pack their DNA?
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Yes
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Is prokaryotic chromosomal DNA circular or linear?
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It can be both
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What is a plasmid?
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a small, autonomous, self-replicating, extrachromosal element composed of circular and linear double stranded DNA. It serves as a vehicle for virulence factors and thus disseminate of AB resistance.
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VIP
Descibe what conjugative plasmids do? |
They autonomously transfer themselves from one host to another, passing on virulence factors, and thus AB resistance.
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What is a non-conjugative plasmid? What are they used for?
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A plasmid that can not transfer themselves however can be transferred by a conjugative plasmid. These are used for genetic engineering.
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VIP
Describe a bacteriophage (aka phage): |
A viral genome of either RNA or DNA that can be single or double, linear or circular, short or long - carrying genes are that encoude virulence factors
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What are the two lifestyle choices of a bacteriophage?
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Lytic (productive) infection - after infection, the viral genome replicates and causes the host cell to lyse which allows progeny virus' to be released into the environment
Lysogenic (latent and temperate) infection: after infection, virus does not replicate because all the genes for lytic infection are being repressed. Thus the lysogenic phase genome (called a prophage), becomes latent. |
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What is a prophage?
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A lysogenic phage genome that is latent. It can either circularize and remain autonous like plasmids or can integrate and become part of the host chromosome.
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VIP
Where does transposition occur? |
WITHIN an individual bacterium
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What is a transposable element (transposition)?
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AKA: Jumping gene - genetic units that mediate their own transfer from one location in a genome to another location with the same genome or from one genome to another.
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Describe the clinical relevance to transposition:
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Transposable elements are major carriers of AB resistance since they can jump from 1 genome to another and find their way to a phage and conjugal plasmids. Using these conjugal plasmids they can transfer genetic material from cell to cell and from species to species.
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VIP!
Can transposons (transposable elements) transfer DNA from 1 cell to another? |
No!
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What is an IS element?
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A transposable element (insertion sequence) that is a segment of DNA that only carries genes for its own transcription. These genes carry a site specific RECOMBINASE and two distinct nucleotide recognition sequences located at both termini. These IS elements insert into plasmids via transposition (recognition of terminal sequences)
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What is a transposon?
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Another transposable element that builds on the IS element. It is a hybrid the consists of a central core of genes bounded by 2 IS elements that carry genes necessary for transposition. The core genes can encode a variety of functions including resistance to AB's.
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What is a transposable prophage?
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Another transposable element (this one is aka bacteriophage). After infection a phage can integrate virtually anywhere in a chromosome and can transpose itself to another location. Later it can under the lytic process to create new infectious phages.
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What is a conjugal transposon?
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A complex of two IS elements that flank genes that encode AB resistance and conjugal machinery. This multiple resistant transposons jump from location to location with in a cell. Also, since they carry genes for conjugation they can mediate their own transfer to other cells.
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What kind of bacteria use conjugal transposons?
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Gram - and gram +
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How are R-plasmids formed?
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By transposing a transposon or IS element into a conjugal plasmid -- this generates an R plasmid that carries multiple virulence factors. It can mediate its transfer from one host to another. And is also resistant to multiple antibiotics.
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Specifically what two things can R-plasmids do that makes them resistant to multiple drugs?
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Can encode enzymes that:
1. inactivate AB's 2. reduce permiability to AB |
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Since R plasmids carry multiple drug resistances what do nonpathogenic bacteria (bacteroide) that carries an R plasmid do?
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These nonpathogenic bacteria act as a reservior of our plasmid for pathogenic bacteria.
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What role do transposons play in the dissemination of AB resistances
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Transposons carry genes that can encode for a variety of functions including resistance to AB's
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How do cells acquire resistance?
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They acquire large pieces of DNA from bacteria that encode ways to get around mechanisms that kill them
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VIP
How is informatino in transformation, conjugation, and transfuction all shared? |
Using a one-way transfer of DNA from a donor cell to a recipient cell.
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What are endogenotes and exogenotes?
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Endogenote: cell's own chromosomes in recipient
Exogenote: molecule of DNA introduced into a recipient from a donor |
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What three ways is genetic information shared between species?
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Transformation
Conjugation Transduction |
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Two steps of transformation:
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1. release of naked DNA into environment by lysis (or pumping out) of donor cells
2. uptake of that DNA by other cells (the recipients) that are "competent" (able to uptake DNA from environment. |
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Explain competency. Is a cell always competent?
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Competency: cells ablility to uptake DNA from environment.
Genes that encode competency are turned on only under certain environmental conditions. |
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What is the clinical relevance to transformation?
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Gram + and - bacteria use transformation to change their appearance of clinically important surface antigens, there by evading host's immune system.
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After a competent bacteria uptakes DNA what are the three fates of that DNA?
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1. degradation - no heritable change in recipient
2. circularization - if it can replicate, it will be inherited as a plasmid 3. recombined into the chromosome |
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VIP
What is conjugation? |
When two cells cuddle up next to each other (contact!) and donor cell releases a conjugal plasmid (via a conjugal bridge)into the recipient using rolling replication.
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What is the clinical relevance of conjugation?
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AB resistance is carried by conjugal plasmids called R plasmids. These can mediate conjugation between one bacteria cell and another and also cross species. Therefore conjugation of R plasmids can cause rapid dissemination of AB resistance.
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How can conjugation be disrupted?
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By shaking
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VIP
What is the most frightening scenerio having to do with conjugation and AB resistance? |
The evolution of a multiple resistant conjugal plasmid in a reservior of benign commensal bacterial followed by conjugal transfer to extremely pathogenic bacteria that could otherwise be easily treated
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How is a sex pilus involved in conjugation?
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It captures recipient, forming mating pair.
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VIP
Is DNA ever naked in conjugation as in transformation? |
NO!!!!!
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What is transduction?
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A form of gene transfer mediated by bacterial virus' (bacteriophage)
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When do bacteriophages reproduce? What does this make them?
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Bacteriophages reproduce only with in bacterial cells. This makes them obligate parasites.
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What is the clinical relevance of transduction?
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The bacteriophage can carry virulence factors including toxins (beta-phages and CTX phages produces toxins) that can be released when the cell lyses.
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VIP
What does a CTX phage produce? |
Cholera toxin
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What is the two step process the phage uses to infect a sensitive cell?
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1. ADsorption or binding to a specific receptor on that cell's surface
2. injecting its genome into the interior of the cell. ???? |
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What is a temperate phage?
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Another name for a lysogenic phage.
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What is a lysogen?
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A cell harboring a latent prophage (dormant bacteriophage) that is capable of becoming lytic.
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Does transduction require cell:cell contact like conjugation?
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No
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During transduction, is DNA ever naked? What protection does it have?
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Never naked, the phage is protected by a capsid so it is resistant to nucleases and detergents.
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Can phages jump from species to species like in conjugation?
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No, phages are generally limited to their own species. Therefore there is a limited cross species exchange.
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