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98 Cards in this Set
- Front
- Back
Define mutation |
change in the nucleotide sequence in the genome of an organism |
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Define genetic recombination |
genetic rearrangements in the genome |
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Prokaryotes do not have ______ reproduction. |
sexual |
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Prokaryotes exchange genetic information (T/F) |
True |
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What is a point mutation? |
Involves a single base mutation |
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What are the three different point mutations? |
Missense Nonsense Silent mutations |
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What do frameshift mutations result in? |
Frameshift mutations result in change in the reading frame. Insertion or deletions |
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Frameshift mutations (picture) |
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What are two examples of chemical mutagens? |
Base analogs Intercalative dyes |
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Define base analogs |
substitutes for bases in DNA. Pair with the wrong base - induce a mutation |
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Define intercalative dyes |
Ethidium bromide. Causes abnormal DNA conformation and results in inserations/deletions |
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What are two types of radiation? |
Ionizing radiation nonionizing radiation |
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Define ionizing radiation |
X-rays, cosmic rays, gamma rays. Generate hydroxyl radicals that can mutate the DNA |
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Define nonionizing radiation |
UV light. Bases of DNA absorb UV light and generate altered DNA structures |
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DNA repairs systems act to do what? |
DNA repair systems act to repair damaged DNA prior |
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When is SOS repair system activated? |
SOS repair - activated by DNA damage |
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What is SOS repair system usually repressed by? |
LexA |
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When LexA is inactivated what happens? |
LexA inactivated by RecA when DNA damage occurs |
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What does SOS repair induce? |
Induces error-prone DNA, called mutases Also induces error-free mechanism |
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What does RecA bind to? |
RecA binds preferentially to single-stranded DNA to form a RecA-DNA filament |
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What does RecA form when it binds to single-stranded DNA? |
RecA-DNA filament |
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What does the RecA-DNA filament act to do? |
The filament acts to catalyze LexA cleavage. (single stranded DNA is increasingly formed following DNA damage...) |
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Non-SOS repair is basically error-_____, but SOS repair is error-_____. |
free prone |
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Why is UV a mutagen? |
Because SOS repair is error prone |
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It is better to survive with genetic errors than to die. (T/F) |
True |
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What is the Ames test used to determine? |
Used to determine the mutagenicity of a compound - related to the carcinogenicity (high correlation) |
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What does a Ames test use? |
Use a mutant strain and screen for mutations that repair the defect (revertants) |
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Important things to remember about Ames test |
Important that the mutation is a point mutation Also has a mutation in the error-proof DNA repair mechanism |
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How is the compound tested in the Ames Test? |
The compound tested is first "activated" by incubation with liver enzymes |
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Example of Ames test using Salmonella |
A histidine mutant of salmonella is grown on medium without histidine, cells do not grow A filter containing water or a test compound was placed on the plates Revertants are increased in the presence of the test compound, revealing it to be a mutagen |
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About what fraction of chemicals turn out positive to be rodent carcinogens? |
About three-fourths of chemicals that are positive in the Ames test are found to be rodent carcinogens, but not all substances that cause cancer in laboratory animals are mutagenic in this assay. |
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All substances that cause cancer in laboratory animals are mutagenic in the Ames assay. (T/F) |
False. Not all substance that cause cancer in laboratory animals are mutagenic in this assay |
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Why is the Ames test used even though it is not completely precise? |
The ease, rapidity (results in 3-4 weeks) and low cost of the text make it an important tool for screening substances for potential carcinogenicity |
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How long does it take to get results from an Ames test? |
about 3-4 weeks |
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Define genetic recombination |
the physical exchange of genetic material between genetic elements |
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Define homologous recombination |
Exchange between homologous DNA sequences from different sources |
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What does homologous recombination require? |
Requires RecA protein Homologs of RecA have been found in all species |
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Homologs of RecA have been found in all species. (T/F) |
True |
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What does RecA bind to? |
RecA binds to single-stranded DNA and catalyzes stand invasion of recipient DNA |
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What does RecA catalyze? |
catalyzes strand invasion of recipient DNA |
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What does DNA strand exchange generate? |
DNA strand exchange generates a crossover structure, called a Holliday junction |
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Define holliday junction |
A mobile junction between four strands of DNA |
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What does the resolution of Holliday junction produce? |
Produces recombinant products |
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Holliday Junction/Rec A (picture) |
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Who is Holliday junction named after? |
The structure is named after Robin Holliday, who proposed it in 1964 to account for DNA exchange during meiosis in yeast |
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When did Robin Holliday propose Holliday junctions? |
1964 |
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Why did Robin Holliday propose Holliday junctions? |
To account for DNA exchange during meiosis in yeast |
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What are the 4 methods to exchange genetic material? |
Transformation Transduction Conjugation Nanotubes |
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Define Transformation |
a cell takes up DNA from the environment |
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Define Transduction |
DNA is transferred from one cell to another by a virus |
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Define conjugation |
DNA is transferred by cell to cell contact |
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Define competence |
The ability to take up DNA from the environment |
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There are many ______ involved in transformation. |
Genes |
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What genes are involved in transformation? |
Membrane-associated DNA binding proteins, cell wall autolysins, nucleases |
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Natural competence occurs in only a few Bacteria. (T/F) |
True |
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What is an example of a bacteria that has natural competence |
Bacillus subtilis |
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What is Bacillus subtilis' competence controlled by? |
Competence controlled by quorum sensing pathway |
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E. Coli is naturally competent. (T/F) |
False. E. Coli is not naturally competent |
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How can you make E. Coli competent? |
Treat with high concentrations of Ca2+ and then chill |
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How does a cell integrate transforming DNA |
the DNA binds to a DNA binding protein on cell membrane DNA is taken up - can be degraded by a nuclease as it enters the cell Bound by competence specific ssDNA binding proteins in cytoplasm |
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What does RecA bind to when a cell is integrating transforming DNA? |
RecA binds to the DNA and integrates it into the genome (by homologous recombination) |
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What are the two types of transduction? |
Generalized transduction Specialized transduction |
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Define generalized transduction |
Transfers DNA from any region on chromosome |
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Define specialized transduction |
transfers DNA from a specific region |
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Describe the process of generalized transduction |
Virus infects a cell Accidentally packages some of the host cell's DNA into a viral particle - transducing particle Tranducing particle infects a new cell The donor's DNA recombines with the recipients genome |
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Define transducing particle |
A viral particle that a virus accidently packaged some of the host cell's DNA into |
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Generalized transduction (picture) |
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Describe the normal process of specialized transduction |
Phage DNA inserts into host DNA. Always in same location Becomes induced and excises out of chromosome Make more phage particles |
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Specialized transduction - normal (picture) |
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Describe specialized transduction when it is not perfectly normal |
Sometimes excises a piece of the host's DNA Packed into the phage particle The transducing particles can transfer the genes to a new cell |
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Specialized transduction - not normal (picture) |
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Conjugation is bacterial sex (T/F) |
True |
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Conjugation is what type of mechanism |
Plasmid encoded mechanism -conjugative plasmid |
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What do conjugative plasmids contain? |
Conjugative plasmids contain an operon that codes for proteins involves in DNA transfer, replication, and mating pair formation |
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Other genetic elements can be transferred at the same time during conjugation. (T/F) |
True |
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Cells that contain conjugative plasmids can not act as ______ |
recipients |
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What happens when a cell contains a conjugative plasmid? |
transfer is blocked by proteins encoded by the plasmid |
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Who discovered that cells that contain conjugative plasmids cannot act as recipients |
Discovery - 1953, Lederberg found that mixing of two auxotrophic bacteria could produce a prototrophic one |
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Define donor cell |
contains a conjugative plasmid |
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What does the donor cell code for? |
codes for a sex pilus |
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What does the Pilus bind to? |
Pilus binds to receptor on recipient cell - pulls it closer |
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How is the Plasmid copied? |
Plasmid is copied by rolling circle replication. The displaced strand is transferred |
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Where does second strand synthesis occur? |
Second strand synthesis occurs in recipient |
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Rolling circle replication (picture) |
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What do some conjugative plasmids integrate? |
Some conjugative plasmids can integrate into the chromosome - episome |
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Define episome |
Some conjugative plasmids can integrate into the chromosome |
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What is an example of an episome? |
F plasmid in E. Coli |
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When the plasmid is integrated into the chromosome called _____ - _____/______/______/_____ |
Hfr high/frequency/of/recombination |
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What does Hfr lead to? |
Leads to transfer of chromosomal genes |
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Archaea contain _____ circular chromosome |
single |
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Genetic manipulation of Archaea lags behind Bacteria. (T/F) |
True |
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Give two examples of how genetic manipulation of Archaea lags behind Bacteria. |
Most antibiotics do not effect Archaea No single species is a model organism for Archaea |
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Examples of transformation, transduction, and conjugation do not exist in Archaea. (T/F) |
False. They do exist. |
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______ works reasonably well in Archaea. |
Transformation |
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Define Nanotubes |
Small tubes linking different species |
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Bacteria exchange cytoplasmic molecules (T/F) |
True |
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Why should we care about genetic exchange in bacteria? |
Plasmids often confer resistance to antibiotics Virulence plasmids - can encode for toxins that promote disease Horizontal gene transfer |
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Define virulence plasmids |
Can encode for toxins that promote disease |