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