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19 Cards in this Set
- Front
- Back
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bacteria/viruses are good models for genetic studies because: |
-rapid reproduction -many progeny produced -allows all mutations to be expressed directly -growth in labs is easy/requires little space -small genomes -techniques for isolating and manipulating genes -medically important -genetically engineered for commercial products |
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bacterial phenotypes |
-3 letters: designate related phenotype -=/-: presence or absence of a specific character -r/s: resistant or susceptible to compound -lac- (unable to use lactose) & lac+ ( can use lactose) -str-r (streptomycin resistant) & str-s (streptomycin susceptible) -leucine example (pic) |
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three mechanisms of genetic exchange among bacteria |
1. conjugation 2. transformation 3. transduction |
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conjugation overview
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-DNA transferred from donor cell to recipient cell via cell-to-cell contact -allows for exchange of genetic material between bacterial stains -"sexual" reproduction: not true sexual reproduction, no gametes -"parasexual" process: transfer of genetic material occurs in one direction (not back and forth) -involves plasmids
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Lederberg & Tatum experiment
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-what one was lacking, the other could produce -minimal media: media not supplying full complement of nutrients -final sample: colonies can produce amino acids/vitamins they need on their own (in minimal media) |
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Davis experiment |
-proved need cell-to-cell contact for conjugation |
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conjugation mechanism |
-physical contact via a pilus (conjugation tube) -F plasmid in E. coli encodes genes necessary to make pilus -plasmid transferred donor (F+) --> recipient (F-) -ssDNA is transferred (rolling circle replication) -becomes dsDNA in recipient (now F+) -F plasmids are low-copy-number plasmids: replication once per cell cycle and segregate to both daughter cells during division??? |
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transformation |
-donor DNA molecule (free DNA molecule) is taken up from surrounding medium and incorporated into genome of recipient cell |
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transformation mechanism |
1. donor DNA binds to recipient cell surface 2. donor DNA then moves across cell surface 3. one strand of donor DNA degrades, other strand pairs with recipient host cell DNA 4. donor DNA is integrated into recipient DNA: transformed: recombinant region in host cell (one mutant strand and one original strand) -in cell division: transformed daughter cell + non-transformed daughter cell |
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transduction |
-DNA transferred from one bacterial cell to another via bacteria virus: bacteriophage ("phage") -errors in viral life cycle --> bacterial genes incorporated into a phage capsid head (normal viruses carry viral DNA) -virus injects genes into another bacteria, transferring genetic material from one bacterial strain to another |
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phage life cycle
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-can switch to lytic cycle at any time 1. lytic: -virus begins to function and degrades the bacterial DNA -viral DNA gets replicated and produces proteins that make new phages -phages burst from cell |
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Lederberg-Zinder experiment |
-generalized transduction recombination -u tube: shows difference between conjugation and transduction (phototrophic cells were produced) -transduction: genetic exchange without cell-to-cell contact |
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transduction mechanism (pic) |
1. phage infects bacteria 2. bacterial chromosome gets fragmented 3. some bacteria genes get incorporated into phages 4. cell lysis releases transducing phages 5. if the phage transfers bacterial genes to another bacterium, recombination may take place and produce a transduced bacterial cell |
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viral genetics |
-viruses can infect bacteria, plants, animals, humans -present in large numbers - even at a modest mutation rate, variants with altered properties appear ➡️ HIV, Ebola, West Nile virus, bird flu, H1N1 -viruses can't reproduce without help of host -not living organisms ➡️ genetic parasites |
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DNA viruses |
-ss and ds -very efficient use of DNA by overlapping reading frames -multiple genes within a gene |
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retroviruses |
-RNA genomes are converted to dsDNA by reverse transcriptase -integrate into host genome -transcription by host transcriptional machinery (genes expressed by host cell) -Baltimore classification system: what start with (how get mRNA) |
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retroviruses |
-RNA genomes are converted to dsDNA by reverse transcriptase -integrate into host genome -transcription by host transcriptional machinery (genes expressed by host cell) -Baltimore classification system: what start with (how get mRNA) |
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retrovirus replication |
1. attach to host cell membrane receptors 2. inject RNA 3. reverse transcriptase attaches to RNA 4. reverse transcriptase changes RNA ➡️ cDNA 5. RNA is degraded and reverse transcriptase synthesizes second strand of cDNA 6. cDNA enters nucleus and is integrated into the host cell's DNA ➡️ provirus 6. proviral DNA gets transcribed/translated to make more viruses 7. new viruses lyse out of the cell and go on to infect other cells |
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HIV |
-two types HIV-1 and HIV-2 (+ subtypes) -Africa in 1940-50s ➡️ mutated form of SIV from either chimpanzee (HIV-1) or sooty mangabey (HIV-2) -attacks T-lymphocytes -spread via needles, blood contact, blood transfusion, unprotected sex |
