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What us mutation?
Heritable change in DNA sequence that can lead to a change in phenotype.
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What is a mutant?
A strain of any cell of virus differing from parental strain genotype( nucleotide sequence of genome)
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_______ refers to strain isolated from nature.
Wild-type strain
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What are selectable mutations?
Mutations that give the mutant a growth advantage under certain environmental conditions.
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What are nonselectable mutations?
- Those that usually have neither an advantage nor a disadvantage over the parent.
- Screening checks for this
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Screening is more tedious than selection. (true or false)
True
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_____ is available to facilitate screening.
Replica planting
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Replica planting is useful for identification of cells with a nutritional requirement for growth. Cells such as this are known as ____.
Auxotrophs
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protorophs are ?
The the parents from which an auxotroph mutant has been derived
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What is induced mutation?
Mutations made deliberately.
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What are spontaneous mutations?
Those that occur without human intervation.
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How do spontaneous mutations occur?
Can result from exposure to natural radiation or oxygen radicals.
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Point mutations are what?
Mutations that change only one base pair.
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What can point mutations lead to?
To single amino acid change in a protein or no change at all.
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What is a silent mutation?
Does not affect amino acid sequence.
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What is a missense mutation?
- Amino acid changed
- polypeptide altered
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Whats a nonsense mutation?
- Codon becomes stop codon
- polypeptide is incomplete
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What are frameshift mutations?
- Deletions or insertions that result in a shift in the reading frame
- Often result in complete loss of gene function
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____ and ____ cause more dramatic changes in DNA.
Deletions and Insertions
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What kind of mutations are typically reversible?
Point mutations
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What is Reversion?
Alteration in DNA that reverses the effects of a prior mutation
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What is a Revert?
Strain in which priginal phenotype that was changed in the mutant is restored
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What are two types of Revertants?
Same-site revertant, Second-site revertant
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What are same-site and second-site revertants?
- Same-site: mutation restoration activity is at the same site as original mutation
- Second-site: Mutation is at a different site in the DNA.
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What are mutagens?
Chemical, physical, or biological agents that increase mutation rates
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What do nucleotide base analogs resemble?
Nucleotides
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Acridines are intercalating agents, what do they cause?
Frameshift mutations
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What are the two main types of mutagenic electromagnetic radiation?
Non-ionizing and Ionizing
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How does Ionizing mutagenic electromagnetic radiation cause mutations?
- Ionize water and produce free radicals
- free radicals damage macromolecules in the cell
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How does Non-ionizing mutagenic electromagnetic radiation cause mutations?
- Purines and pyrimidines strongly absorb UV
- Pyrimidine dimers is one effect of UV radiation
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What are three types of DNA repair systems?
Direct reversal, Repair of single strand damage, and Repair of double strand damage.
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What does each of the three types of DNA repair systems do?
- Direct reversal: mutated base is still recognizable and can be repaired without referring to other strands
- Repair of single strand damage: Damage DNA is removed and repaired using opposite strand as template
- Repair of double strand damage: a break in the DNA, requires more error-prone repair mechanisms.
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When DNA damage is large scale the cell may need to use a different type of repair system such as?
SOS regulatory system
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What is the SOS regulatory system?
- More error prone
- Allows replication to proceed and cell to replicate, but errors are more likely
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Recombination is what?
Physical exchange of DNA between genetic elements
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What is homologous recombination?
Process that results in genetic exchange between homologous DNA from two different sources
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Selective media can be used to detect what?
Rare genetic recombinants
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What is transformation?
Genetic transfer process by which DNA is incorporated into a recipient cell and brings about genetic change
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S-cells and R-cells are different because?
S-cells have capsules
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What are competent cells?
Cells capable of taking up DNA and being changed
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How can competent cells be made to take up DNA?
By using electroporation
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What is transfection?
Transformation of bacteria with DNA extracted from a bacterial virus
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What is transduction?
Transfer of DNA from one cell to another is mediated by a bacteriophage
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what are the two modes of transduction?
Generalized and specialized transduction
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What is general transduction?
DNA derived from virtually any portion of the host genome is packaged inside the mature virion
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What is specialized transduction?
DNA from a specific region of the host chromosome is integrated directly in the virus genome
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What is bacterial conjugation?
Mechanism of genetic transfer that involves cell-to-cell contact
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What are F (fertility plasmid?
- Circular DNA molecule-100kbp
- conatins several transposable elements that allow the plasmid to intergrate into the host chromosome
- contains tra genes that encode transfer functions
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Sex pilus is essential for conjugation and only produced by the ____ cell.
Donor
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Cells possesing non-intergrated F plasmid are called ______, while those containing an intergrated F plasmid are called _____.
F+, HFU (high frequency recombination)
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F' plasmids are?
Previosly intergrated F plasmids that have excised and captured some chromosomal genes
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What are metrodiploid cells?
Bacterial strain that carries two copies of any particular chromosomal segment
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complementation is what?
Process by which a functional copy of a gene compensates for a defective copy.
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Transposable elements can be found where?
In all thee domains of life
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How do transposable elements move?
Transporation
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What are the two main types of transposable elements in bacteria?
IS (Isertion sequence) and Transposon
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What are IS?
- The simplest transposable element
- 1,000 nucleotides lone
- inverted repeats are 10-50 base pairs
- only gene is for the transposase
- found in plasmids and chromosomes of bacteria and Archaea and some bacteriophages
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What are transposons?
- Larger than IS
- may include antibiotic resistance
- Tn5 and Tn10
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What are the two mechanisms for transposition?
Conservative and Replicative
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Conservative transposition is?
Transposon is excised from one location and reinserted at a second location(Tn5)
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Replicative transposition is?
A new copy of a transposon is produced and inserted at a second location.
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