Ch 8 Micro
DNA-mediated transformation
"naked" DNA is taken up from the environment by a bacterial cell
phenotype
An organism's observable physical characteristics.
replica plating
Technique for the simultaneous transfer of organisms in separated colonies from one medium to another.
carcinogens
chemicals that cause cancer; most are mutagens
Which of the following can be transferred from one cell to another by conjugation?
chromosomal DNA; plasmid DNA
haploid
contains a single set of genes
______ mutations are generally themes harmful to cells because they change all of the codons downstream of the mutation
frameshift
Which of the following terms describes the sequence of nucleotides (genetic makeup) of an organism or a cell?
genotype
An organism that does not require growth factors is called a(n)
prototroph
insertional inactivation
the gene into which a transposon jumps is inactivated by the event; the inserted DNA disrupts the function of the gene
"Jumping genes" or _____ can lead to changes in genotype within a cell or between cells.
transposons
A base substitution that results in a change in the amino acid encoded is called a(n) ______ mutation
missense
Mutation are rare because
most damage is repaired before it is passed on to progeny
Genetic change in bacteria occurs through which two mechanisms?
mutation; horizontal gene transfer
high copy number
occur in many copies in a cell
base substitution
occurs during DNA synthesis when an incorrect nucleotide is incorporated
Repair of nucleotide incorporation errors during the process of DNA replication is accomplished by _____ by DNA polymerase and by ____ repair
proofreading; mismatch
Mutation rates are low because proofreading and ___ mechanisms fix altered or damaged DNA before it can be passed to the progeny
repair
auxotroph
requires growth factors
Conjugation
DNA is transferred during cell-to-cell contact
Transduction
DNA is transferred from one bacterial cell to another by a bacteriophage
In humans, two of the gens associated with the development breast cancer encode enzymes involved in
DNA repair
Model system
E coli; cells grow quickly in small volumes of cheap media and accumulate in very large numbers
Which of the following mutations frequently results in the production of a shortened and non-functional protein because a different set of codons is translated?
Frameshift
narrow host range
can replicate in only one species
mutation
changes the existing nucleotide sequence of a cell's DNA which is then passed to the progeny through *vertical gene transfer*
frameshift mutation
changes the reading frame of the corresponding mRNA molecule so that an entirely different set of codons is translated
Cells that have the ability to take up DNA from the environment are called __ cells
competent
mismatch repair
fixes errors missed by the proofreading of DNA polymerase
The common consequence of a ______ mutation is the appearance of an early stop codon that produces a shortened and this non-functional protein
frameshift
spontaneous mutations
genetic changes that result from normal cell process; they occur randomly and genes. mutate spontaneously at infrequent but characteristic rates
natural selectin
selection by the environment of the best cells able to survive in that environment
DNA-mediated ____ involves the uptake of "naked" DNA by competent bacterial recipient cells
transformation
Conjugation, DNA-mediated ___ and _____ are methods of horizontal gene transfer in bacteria
transformation; transduction
Which of the following are methods of gene transfer in bacteria?
transformation; transduction; conjugation
Sequences of DNA that can move to new positions within the genome of a single cell are called
transposons
A point mutation involves any substitution of a single nucleotide
true
indirect selection
used to isolate an auxotrophic mutant from a prototrophic parent strain.
Ames test
uses histidine-requiring auxotroph of Salmonella typhimurium to measure the mutagenicity of a chemical
point mutation
when only one base pair is changed
missense mutation
when the altered codon codes for a different amino acid
If a scientist is working with bacteria that have the typical phenotype of those isolated from nature, the bacteria are considered to _____ type.
wild
Recognition and repair of errors in nucleotide incorporation by DNA polymerase is called
proofreading
Errors by DNA polymerase that incorporate the wrong nucleotide into replicating DNA can be repaired quickly by which two mechanisms?
proofreading by DNA polymerase; mismatch repair
Bacteria are a great model system for genetic studies because when they are grown to very high numbers in small volumes of simple media _________.
rare genetic changes that happen can be easily studied
_____ sometimes incorporates the incorrect nucleotide when generating a new strand of DNA during DNA _____; this leads to a detectable distortion in the DNA helix
DNa polymerase; replication
broad host range
can replicate in many different species
SOS repair
damaged DNA activates expression of several dozen genes that encode for the SOS system
genotype
sequence of nucleotides in the DNA
low copy number
occur in one or a few copies per cell
_______ are circular pieces of bacterial DNA that do not usually encode information essential to the life of a cell
plasmids
The return of a gene from a mutated state to its original, non-mutated state is called a
reversion
replicon
the DNA has an origin of replication; plasmids and chromosomes
The process in which better adapted organisms reproduce at higher rates in a given environment is called
natural selection
A base substitution that changes an amino acid-encoding codon to a stop codon is called a(n) ______ mutation
nonsense
SOS mutagenesis
SOS DNA polymerase has no proofreading ability and makes errors
horizontal gene transfer
the movement of DNA from one organism to another
Steps of DNA-mediated transformation
1. Double stranded DNA molecule binds to the surface receptor 2. Nucleases degrade one strand of double-stranded DNA at the cell surface 3. Single-stranded DNA enters the cell after one strand has been degraded 4. Single-stranded DNA integrates into genome after entering the cell 5. Strand being replaced by donor DNA is degraded
reversion (back mutation)
a mutation that changes back to its original and non-mutated state
competent
a specific physiological state that allows the cell to take up DNA
photoreactivation
an enzyme uses the energy of visible light o break the covalent bonds of the thymine dimer; restoring DNA to its original state
proofreading
dna polymerase checks the accuracy of their actions by removing a nucleotide the is not correctly hydrogen-bonded to the opposing nuclease
prototroph
does not require growth factors
homologous recombination
donor DNA becomes positioned next to the complementary region of the recipient cell's DNA; donor DNA then replaces a homologous segment of recipient DNA that is then degraded
excision repair
enzyme recognizes the major distortions in DNA that result from thymine dimer formation and removes the DNA strand with the damaged region
In bacterial conjugation, F+ donor cells are high frequency recombinant cells when the F plasmid
is integrated into the chromosome
transposons
jumping genes or pieces of DNA that can move from one location to another in a cell's genome (transposition)
In this image, the base substitution leading to cysteine is called a(n) ______ mutation
silent
Random genetic changes that occur as a result of natural cellular processes are called ______ mutations
spontaneous
synonymous mutation (silent mutation)
the change generates a codon that translates into the same amino acid as the original
knockout mutation
any mutation that totally inactivates the gene
Consider a population of bacteria susceptible to an antimicrobial, If a bacterium acquires a spontaneous mutation that gives resistance to the antimicrobial, this bacterium will ______ if the population is exposed to the antimicrobial.
grow without competition
In _____ gene transfer, DNA move from one organism to another, while in _________ gene transfer, DNA is passed from a parent cell to its progeny
horizontal; vertical
A point mutation always leads to a shift of the reading frame from the point of mutation downstream
false
direct selection
cells are inoculated onto an agar medium that supports the growth of the mutant and does not allow the parent to grow
A(n) ________ mutation results from an insertion or deletion of nucleotides, leading to a shift of the reading frame from the point of mutation downstream
frameshift
nonsense mutation
occurs when base substitution creates a stop codon that produces a shorter and non-functional protein
penicillin enrichment
selectively kills prototrophs and is sometimes used before replica plating to increase the proportion of auxotrophic mutants.