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General Microbiology Chapters 10 and 11


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an organism that has developed a nutritional requirement through mutation
cloning vector
genetic element into which genes can be recombined and replicated
transfer of genes from one prokaryotic cell to another by a mechanism involving cell to cell contact and a plasmid
gene disruption
use of genetic techniques to inactivate a gene by inserting within it a DNA fragment containing a selectable marker. The inserted fragment is called a cassette, and the process of insertion, cassette mutagenesis. Also called gene knockout.
Genetic map
the arrangement of genes on a chromosome
the precise genetic makeup of an organism; the complete sequence of a cell's chomosomes and plasmids if present
molecular cloning
isolation and incorporation of a fragment of DNA into a vector where it can be replicated
an agent that causes mutation
an organism whose genome carries a mutation
an inheritable change in the base sequence of the genome of an organism
the observable characteristics of an organism
an extrachromosomal genetic element that has no extracellular form
point mutation
a mutation that involves a single base pair
the process by which parts or all of the DNA molecules from two separate sources are exchanged or brought together into a single DNA molecule
more tedious than selection, involves examining large numbers of colonies for nonselectable mutation.
allows the isolation of a single from a population containing millions of parental organisms
shotgun cloning
making a gene library by random cloning of DNA fragments
site-directed mutagenesis
a technique whereby a gene with a specific mutation can be constructed in vitro
transfer of host genes from one cell to another by a virus
transfer of bacterial genes involving free DNA
transposable element
a genetic element that has the ability to move from one site on a chromosome to another
a type of transposable element that carries genes in addition to those involved in transposition
vector (i.e. cloning vector)
a DNA molecule that, on being replicated in a cell, brings about the replication of other genes inserted into the DNA molecule.
wild type
a bacterial strain isolated from nature
suppresor mutations
mutations that compensate for the effect of the original muation and restore the original phenotype
lateral gene flow
(i.e. horizantal gene flow)
genes are transfered from donor to recipient, which allows for recombination and gene transfer
genetic markers
genetically altered strains from gene mutation that are used to detect transfers
mutant phenotype
altered phenotype due to mutation
selectable mutation
the mutation confers a clear advantage on the mutant strain under certain environmental conditions, which makes them able to outgrow and replace the parent strain
replica plating
used to detect nutritionally defective mutants; colonies of parental type grow normally but those of the mutant do not.
penicillin selection method
used to enrich a population of mutagenized cells, the penicillin kills only growing cells (i.e. parental cells).
spontaneous mutations
can occur as a result of exposure to natural radiation that alters the structure of bases in the DNA. the bulk occur during DNA replication as a result of errors in the pairing of bases
point mutations
occur from base-pair substitutions in the DNA.
coding region mutation
change in the amino acid sequence of the polypeptide
silent mutations
almost always occur in the third base of the codon: no phenotypic change
missense mutation
called this because the informational "sense" in the ensuing polypeptide changes, if they occur at a critical point then a protein can be inactivated or have reduced activity.
Nonsense stop codon
this is due to base-pair substitution, usually premature termination of translation
a point mutation in which one purine base is substituted for another purine or one pyrimidine is substituted for another pyrimidine.
point mutations where a purine base is substituted for a pyrimidine base, or vice versa.
Frameshift mutations
caused by any insertion or deletion of a base pair, can result in a complete loss of gene function
insertion sequences
a type of transposable element that is identifiable DNA sequence 700-1400 bp in length.
a large section of chromosomal DNA is moved to a new location because of an error in recombination
a mistake in recombination where the orientation of a particular segment of dna is reversed with respect to the surrounding DNA
Types of revertants
same-site revertants
second-site revertants
true revertants
Classes of suppressor mutations:
1. mutation somewhere else in the same gene that restores enzyme function
2. a mutation in another gene that restores the function of the original mutated gene.
3. a mutation in another gene that results in the production of an enzyme that can replace the mutated one.
Adaptive mutations
generated by mechanisms activated by the organism itself in order to survive a particular stress condition
Nucleotide base analogs
molecules that resemble DNA purine and pyrimidine in structure yet display faulty pairing properties and are chemical mutagens; DNA replication errors occur more often at these sites
Intercalating agents
mutagens which become inserted between two DNA base pairs and in the process push them apart.
pyrimidine dimers
two adjacent pyrimidine bases on the same strand become covalently bonded to one another in such a way that during replication the probability of DNA polymerase misreading the sequence is greatly increased.
SOS regulatory system
DNA damage serves as a distress signal to the cell, resulting in the coordinate expression of a number of cellular functins involved in DNA repair. Normally repressed by the protein LexA.
mutant strains that are still viable but have an increased rate of mutation
have the capability of causing cancer in humans or other animals
Ames test
the mutagenicity test for carcinogens, tests the number of revertants against chemical agents
heteroduplex region
each strand has originated from a different chromosome
Ways of genetic recombination
Transformation, transduction, conjugation
a cell that is able to take up DNA and be transformed
process where bacteria can be transformed with DNA extracted from a bacterial virus rather than from another bacterium
generalized transduction
host DNA derived fom virtually any portion of the host genome becomes a part of the DNA of the mature virion in place of the virus genome
specialized transduction
this occurs only in some temperate viruses: DNA from a specific region of the host chromosome is integrated directly into the virus genome, usually replacing some of the virus genes.
Incompatible plasmids
the second plasmid may not be maintained and is lost during subsequent cell replication
Plasmids can sometimes be eliminated from host cells by various treatments, this process results from inhibition of plasmid replication without parallel inhibition of chromosome replication
R plasmids
plasmids resistant to antibiotics and various other growth inhibitors
The virulence of pathogens
1) the ability of the pathogen to attach to and colonize specific host tissues
2) the formation of substances that cause damage to the host
bacteria that produce proteins that inhibit or kill closely related species or even different strains of the same species
plasmid integration
a mechanism for mobiliing the cell's main genetic resources
Alterations to the properties of the cell caused by the F plasmid
1- the ability to synthesize the F pils
2- the mobiliation of DNA for transfer to anotcel
3-the alteration of surface receptors so the cell is no longer able to behave as a recipient in conjugation
interrupted mating
conjugating cells can be separated by agitatin in a mixer or blender.
cis-trans test
used to determine whether or nt two molecules are in the same genetic unit
a genetic unit, a gene

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