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83 Cards in this Set
- Front
- Back
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What 6 qualities make bacteria so useful to geneticists?
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1. Genomic simplicity
2. Uncomplicated genotypes 3. Rapid generation times 4. Large numbers of progeny 5. Ease of Propagation 6. Numerous heritable differences |
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What does the quality "numerous heritable differences" mean in regards with bacteria?
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Mutants are easily created, identified, isolated, and manipulated for examination.
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What are the 3 mechanisms for transferring DNA in bacteria?
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1. Conjugation
2. Transformation 3. Transduction |
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What is Conjunction?
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The transfer of replicated DNA from a donor bacterium to a recipient bacterium.
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What is Transformation?
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The uptake of DNA from the environment by a recipient bacterium, the change in genotype in the recipient cell
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What is Transduction?
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The transfer of DNA from a donor bacterium to a recipient by way of a viral vector
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What is a Bacterial Chromosome?
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A covalently closed, CIRCULAR molecule of double stranded DNA.
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What are Plasmids?
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Plasmids are small double stranded circular DNA that contain NONESSENTIAL genes (used infrequently or under specialized conditions)
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What are F Plasmids?
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F (fertility) plasmids contain genes that promote its own transfer from a donor to a recipient.
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What are R Plasmids?
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R (resistance) plasmids carry antibiotic resistance genes that can transfer from donors to recipients.
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In conjugation, donor cells are designated as what (F+, F-, or F')? Why?
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F+, to indicate their possession of an F factor
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In conjugation, recipient cells are designated as what (F+, F-, or F')? Why?
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F-, to indicate their lack of an F factor
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Where are the genes that control conjugation located?
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They're located in the genes carried on the F plasmid.
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What are Exconjugant Cells?
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A recipient cell that has had its genetic content modified by receiving donor DNA.
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What are Insertion Sequence Elements?
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Mobile segments of bacterial DNA that are capable of transposing themselves throughout the bacterial genome
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What are Episomes?
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Circular DNA elements that can replicate independently or integrate into the bacterial chromosomes and replicate as part of the chromosome.
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In conjugation, what catalyzes cleavage of one phosphodiester bond on one DNA strand to initiate transferring?
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Relaxosome
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What is a prototroph?
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Wild type bacteria that can synthesize all essential nutrients itself.
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What is an auxotroph?
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Mutant bacteria that is unable to synthesize one or more essential nutrients due to gene mutation
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What is Generalized Transduction?
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The transfer of ANY bacterial gene
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What is Specialized Transduction?
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When temperate phages excise from the bacterial chromosome they may take some bacterial genes with them
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What is a virus?
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A virus is nucleic acids packaged in protein coats (capsids).
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What kind of genomes do Viruses have? double stranded, single stranded? RNA? DNA? Linear or circular?
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Viruses can have it all. DS or SS RNA or DNA, linear or circular.
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What are bacteriophages?
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Viruses that infect bacteria
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Which cycle do virulent phages go through?
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Lytic cycle
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Which cycle do temperate phages go through?
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Lysogenic and sometimes lytic cycle
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Transduction can be used to map genes by measuring what?
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The frequency with which genes are transferred together!
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Phage genes can be mapped by infecting bacterial cells with what?
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Two different strains of phage and counting the recombinants.
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What is the most common transformant?
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Single transformant!
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The rate of cotransformation is inversely proportional to the distances between what?
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The cells!
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In tranformation, if the frequency is 0.9, what does it mean about the distances between the cells?
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They're close together!
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In transformation, close together genes are more likely to do what?
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Transformed together!
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Which type of phages ONLY undergo the lysogenic cycle?
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ONLY TEMPERATE PHAGES!
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During which bacterial phage cycle are new phages released from the bacteria by digesting the host cell?
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Lytic Cycle
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Which cross of F+, F-, F', and Hfr will produce the highest frequency of recombinants?
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A cross between Hfr and F-!
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What is the viral enzyme reverse transcriptase used for?
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It is used to convert the viral RNA genome into a DNA genome!
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What process was used to show that DNA is the genetic material?
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Transformation!
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What are Hfr strains?
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High-Frequency recombination strains have a high rate of recombination with the chromosome of F- recipients.
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Does conjugation between Hfr and F- recipients convert the recipients to F+ or Hfr donors?
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Virtually never.
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What makes Hfr different from F+?
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The F factor in Hfr strains is integrated into the bacterial chromosome.
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What is Interrupted Mating?
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The cessation of conjugation caused by breakage of the pilus tube (takes place naturally).
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What happens when Interrupted Mating occurs?
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Interrupted matings stop conjugation before the Hfr chromosome can be completely transferred.
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What are F' donors?
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Donor bacteria that contain a functional but altered F factor derived from imperfect excision from out of the Hfr chromosome.
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What is the F' factor?
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It is an imprecise copy of the F factor that contains all of its own DNA plus a segment of bacterial chromosomal DNA.
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What are Partial Diploids?
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Exconjugant bacteria that acquire a second copy of one or more genes by conjugation with an F' donor cell.
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What are the 6 steps to the Lytic Cycle?
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1. Attachment of the phage particle to host cell
2. Injection of phage chromosome into host 3. Replication of phage DNA 4. Transcription and translation of phage genes 5. Packaging of phage chromosome into phage heads 6. Lysis of host cell |
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What is Lysogeny?
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Lysogeny is an integration process of temperate phages into the host chromosome.
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What are the 5 steps to the Lysogenic Cycle?
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1. Attachment of the phage particle to host cell
2. Injection of phage chromosome into host 3. Integration of phage chromosome into host chromosome 4. Excision of the prophage 5. Resumption of the lytic cycle |
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What is the Lytic Cycle?
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The life cycle of a bacterium infected by a bacteriophage that replicates within the host cell to produce progeny bacteriophage.
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What is the Lysogenic Cycle?
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Life cycle of a bacterium infected by a temperate bacteriophage that integrates into host chromosome and replicates along with it!
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What is a Temperate Phage?
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A bacteriophage that can integrate into bacterial host chromosome and produce either the lytic or lysogenic life cycle.
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What is a Prophage?
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Prophage is the Phage DNA after its been integrated into the host chromosome!
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In the Lysogenic cycle, what is meant by "excision of the prophage"?
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The prophage reverses its integration and is excised from the chromosome intact.
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What are Generalized Transducing Phages?
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They are phages that are formed when a random piece of donor bacterial DNA is mistakenly packed into the phage head instead of phage DNA.
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What is Cotransduction?
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The simultaneous transduction of two or more genes contained on a donor DNA fragment into a recipient cell where it undergoes homologous recombination to be spliced into the transductant chromosome.
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How is a merozygote formed?
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The F factor and several adjacent genes are excised from the chromosome of an F+ cell and transferred to an F− strain.
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What is the role of Transposase activity in IS elements?
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Cutting DNA at the target sequence!
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What transposition event will mostly likely result in a loss-of-function mutation?
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Insertion of an IS element WITHIN the coding region of a gene.
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How is an Hfr chromosome formed?
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By integration of the F plasmid into the bacterial chromosome
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In what process of genetic exchange in bacteria is one strand of DNA degraded as it enters the recipient cell?
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Transformation!
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What three things are only found in viruses?
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1. Capsomere (core protein
2. Capsid 3. Envelope with glycoproteins |
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What are 3 characteristics that the Lytic cycle has that the Lysogenic cycle lacks?
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1. Host is destroyed
2. cell is lysed 3. new phages are assembled from viral DNA and proteins |
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What are 2 characteristics that the Lysogenic Cycle has that the Lytic cycle lacks?
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1. Integration of Viral DNA into host chromosome
2. Normal cell reproduction |
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When will Capsid enter the host cell?
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If the cell is enveloped!
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Does a retrovirus contain RNA or DNA?
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RNA
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Enveloped viruses bud from what cell?
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The host cell
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HIV contains what kind of transcriptase?
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REVERSE transcriptase!
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How do nonenveloped viruses typically exit the host cell?
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By bursting through the plasma membrane
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How do enveloped viruses generally exit the host cell?
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By budding which because of this, the viral envelope is often derived from the host cell's plasma membrane.
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Which cells can convert exconjugants to a donor state?
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F+ and F' cells
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Which donors can transfer a donor gene to exconjugants?
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F' and Hfr cells
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What was the type of donor cell if the recipient genotype changes in addition to becoming a donor?
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F'
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What was the type of donor cell if the recipient genotype changes but it does not become a donor?
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Hfr
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How is a partial Diploid formed?
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It is formed when a recipient cell receives an F' plasmid from a donor.
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What is the site of integration in transduction called?
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Att site!
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Hfr maps for a given bacterium are consolidated to form what?
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To form a genetic map of the donor chromosome as a whole
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How are F' strains created?
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Created when excising of an F factor from Hfr integration removes F factor DNA along with adjacent donor chromosome DNA
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Conjugation between F' and F- recipient generates what?
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Partial diploidy in exconjugants!
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Transforming DNA undergoes what with the recipient chromosome to produce transformants?
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Undergoes homologous recombination!
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When do recipient cells undergo generalized transduction?
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When donor DNA introduced by a generalized transducing phage recombines with the recipient chromosome.
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Cotransduction mapping determines the order of what?
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The order of genes on DONOR chromosomes!
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How are Specialized Transducing Phages produced?
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Produced by the aberrant excision of a lysogenic prophage that removes a portion of the prophage and an adjacent segment of host DNA.
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Specialized transduction is limited to the transduction of genes where?
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Adjacent to the site of prophage integration!
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