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67 Cards in this Set
- Front
- Back
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Do plasmids replicate independently of the host chromosome?
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yes
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Plasmids range in size from ___ to ___ and are typically less than ___% o the chromosome size
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1kbp to 1Mbp
5% |
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define plasmid incompatibility
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when one copy of a plasmid is lost in replication due to the cell containing more than one copy of a genetically related plasmid
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define episomes
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plasmids that can integrate into the cell chromosome
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define curing
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removal of plasmid from host cell by various treatments
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how does curing work?
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inhibition of plasmid replication without parallele inhibition of host chromosome replication
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define conjugative plasmid
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plasmids that govern their own transfer by cell-to-cell contact
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T/F: all plasmids are conjugative
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false
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what is the region of on the plasmid that contains the genes for transfer by conjugation?
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tra
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how can the tra region affect a chromosome?
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if the plasmid that contains a tra region is integrated into the chromosome then the whole chromosome can be mobilized and transferred from one cell to another
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name a conjugative plasmid that has a broad host range and state what this means
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Pseudomonas, broad host range means that its plasmids are transferable to a wide variety of other gram-negative bacteria
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What types of organisms can plasmids be transferred to?
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-distantly related organisms
-gram-negative/gram-positive -bacteria cells and plant cells -bacteria and fungi |
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Location-Visceral
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pain arising from organs or hollow viscera is often perceived in an area remote from the organ causing the pain
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What are R plasmids?
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plasmids that confer resistance to antibiotic and various other growth inhibitors
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Are all resistance genes carried by a single R plasmid?
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they can be; other cells carry multiple resistance plasmids
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how do resistance genes work?
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encode proteins that inactivate the antibiotic or protect the cell by some other mechanism
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What is a bacteriocin and what does it do?
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a bacteriocin is a protein that the bacteria produces to kill/inhibit different/closely-related strains of the same species
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How do bacteriocins differ from antibiotics?
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bacteriocins have a narrower spectrum of activity
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Genes encoding for bacteriocins are usually carried on _____ or ________
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plasmids/transposons
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Define a mutation
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heritable change in DNA sequence that can lead to a change in phenotype
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Define a mutant
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a strain of any cell or virus differing from parental stain in genotype
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Define a selectable mutation
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mutation that gives the mutant a growth advantage under certain environmental conditions
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Define a non-selectable mutation
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a mutation that gives the mutant neither an advantage nor disadvantage.
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how do you detect a non-selectable mutation?
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examine a large number of colonies and look for differences
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Define a point mutation
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mutations that change only one base pair
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Define a missense mutation
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an amino acid is changed and the polypeptide is altered
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define a nonsense mutation
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when a codon becomes a stop codon, and the polypeptide is incomplete
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T/F deletions and insertions cause more dramatic changes in DNA
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true
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Framshift mutation
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-deletions or insertions that result
in a shift in the reading frame -often results in a complete loss of gene function |
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What type of mutations are usually reversible?
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point mutation
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what are the two types of revertants?
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-same-site revertant
-second-site revertant |
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Smaller the genome, the higher/lower the mutation rate
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higher
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Why does RNA have a higher mutation rate than DNA?
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-only some RNA polymerases have proofreading abilities
-comparable RNA repair mechanisms do not exist |
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What does the Ames test test for?
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Mutagenesis
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Define recombination
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physical exchange of DNA between genetic elements
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Explain homologous recombination
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-endonucleases nicks on strand of the DNA molecule
-helicase activity displaces the nicked strand from the other -SSB protein binds to the single stranded segment -RecA protein binds to the SS region, forming a complex that facilitates annealing with the complementary sequence in the DNA duplex |
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Transduction
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transfer of DNA from one cell to another is mediated by a bacteriophage
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What are the two types of transduction?
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-Generalized
-Specialized |
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Generalized transduction
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DNA derived from virtually any portion of the host genome is packaged inside the mature virion
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Specialized transduction
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DNA from a specific region of the host chromosome is integrate directly in the virus genome
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In what type of bacteria does specialized transduction occur?
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-temperate bacteria
-only during lysogeny |
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Give the 3 characteristics of generalized transduction
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-defective virus particles incorporates fragments of the cell's chromosome randomly
-can be temperate or virulent -low efficiency |
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Describe what happens during generalized transduction
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-phage attaches
-induces the lytic cycle -enzymes that pack viral DNA into bacteriophage pack host DNA by accident |
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What's the difference between virions and transducing particles?
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-virion=contain phage genes
-transducing particles=only contains the host's genes |
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Define bacterial conjugation (mating)
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mechanism of genetic transfer that involves cell-to-cell contact
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GIve 3 characteristics of bacterial conjugation
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-plasmid encoded mechanism
-donor cell contains conjugative plasmid -recipient cell does not contain the plasmid |
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T/F: the fertility plasmid contains several transposable elements that allow the plasmid to integrate into the host chromosome
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true
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What structure is essential for conjugation and only produced by the donor cell?
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sex pilus
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Is DNA synthesis necessary for DNA transfer by conjugation?
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yes
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During conjugation, how is DNA synthesized?
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rolling circle replication
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Define merodiploid
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bacterial strain that carries two copies of any particular chromosomal segment
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define complementation
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process by which a functional copy of a gene compensates for a defective copy
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Complementation tests are used to...
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-determine if two mutations are in the same or different genes
-see if the mutation is in a particular gene |
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Define transposable elements
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discrete segments of DNA that move as a unit from one location to another within other DNA molecules
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Which domains of life can transposable elements be found?
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all three
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Define transposition
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-the process by which transposable elements are moved
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Who observed transposition first?
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Barbara McClintock
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What are the two main types of transposable elements in Bacteria?
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1. transposons
2. insertion sequences |
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T/F only transposons carry the genes encoding for transposase
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false; both insertion sequences and transposons carry these genes
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T/F both transposons and insertion sequences have inverted repeats at their ends
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true
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Which transposable element is the simplest?
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insertion sequences
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Give the 4 characteristics of insertion sequences
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-~1000 nt long
-inverted repeats are 10-50bp long -only gene is for transposase -found in plasmids and chromosomes of bacteria and Archaea and some bacteriophages |
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How do transposons compare in size to insertion sequences?
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transposons are larger
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What does transposase do?
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moves any DNA between inverted repeats
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What are the two known mechanisms of transposition?
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-conservative
-replicative |
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Define conservative transposition
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transposon is excised from one location and reinserted at a second location
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Define replicative transposition
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a new copy of a transposon is produced and inserted at a second location
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