Chapter 8
The consequences of not repairing damaged DNA in cells include _____
-cell death -cancer (in animals)
Mutations that are caused by external influences such as radiation or chemicals are called _____ mutations
induced
These chemicals, produced in aerobic environments, lead to the oxidation of guanine in DNA resulting in increased base substitutes
reactive oxygen species (ROS)
After new virus particles have assembled in the bacterial host cell, they are usually _____
released as a result of host cell lysis
Extensively damaged DNA activates the _____ repair mechanism, which cannot always determine the correct nucleotide sequence, thus introducing mutations resulting from the repair process itself.
SOS
Plating bacteria in duplicate patterns on both a nutrient agar plate and a glucose-salts agar is an example of _____ platting
replica
The two types of transduction are _____
specialized and generalized
Ultraviolet radiation causes a very specific type of DNA damage called ______
thymine dimers
In insertion sequences, the _____ gene (the only gene) is flanked by _____ repeats
transposase, inverted
When some species of bacteria reach a certain density or when nutrients are in short supply, they _____
turn on genes required for competence
If a scientist is working with bacteria that have typical phenotype of those isolated from nature, the bacteria are considered to be _____ type
wild
Random genetic changes that occur as a result of natural cellular processes are called _____ mutations
spontaneous
Recognition and repair of errors in nucleotide incorporation by DNA polymerase is called _____
Proofreading
In penicillin enrichment, the penicillin selects against the _____ which can grow in the medium
Prototrophs
Replica plating is a form of _____ selection in which duplicate patterns of colonies are plated onto nutrient agar and a plate with glucose-salts agar.
indirect
Which of the following are characteristics of recombinants?
-they have properties of both donor and recipient cells -they result from horizontal gene transfer
Examples of conditions where bacteria can become naturally competent in the environment include _____
-when there is a high density of bacteria -when certain nutrient are scarce
Chemical mutagens can cause which of the following?
-Base substitutions -Frameshift mutations
X rays can cause which types of damage to a DNA molecule?
-Nucleobase alterations -Single stranded breaks -double stranded breaks
Which of the following are systems bacteria can use to protect against invading DNA?
-Restriction-modification -CRISPR
The largest group of chemical mutagens consists of
Alkylating agents
_____ 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
In humans, two of the genes associated with the development of breast cancer encode enzymes involved in _____
DNA repair
DNA transfer by conjugation is more efficient in a liquid medium setting, subjected to very mild agitation (stirring), rather than on an agar plate format. Why?
Direct cell-to-cell contact is required for this process, and this is more likely to be achieved in the fluid liquid format than on an agar plate (especially for relatively non-motile types of bacteria)
Which type of mutation alters the reading frame of a gene?
Frameshift
_____ selection is used to isolate an auxotroph from a prototrophic parent strain, because no selective medium exists to inhibit the parent
Indirect
Which is true about a crown gall tumor?
It results from the incorporation of bacterial plasmid DNA into the plant chromosome
Protection against the toxic effects of antimicrobial compounds or heavy metals is often found to be encoded on ___
R plasmids
_____ is the change of a mutated genetic sequence back to its original, non0mutated form
Reversion
The restriction-modification system always has two genes involved, the cutting enzyme and the methylating enzyme
True
When bacteriophages replicate, phage components are synthesized in the host cell and assemble into new viruses _____
Within that cell before bing released
_____ are a type of radiation that can cause single and double stranded breaks in a DNA strand
X Rays
The study of the crown gall tumor found
a bacteria plasmid promoter that was similar to plant promoters
Which of the following plasmids encodes an origin of transfer?
both conjugative and mobilizable plasmids
Unlike stranded DNA polymerase, the DNA polymerase used in SOS repair _____
can synthesize DNA even in very damaged regions
Chemicals that cause cancer are called _____
carcinogens
The general mechanisms by which most bacteria routinely respond to new circumstances are _____ change and regulating _____ expression
genetic; gene
To increase the chance of detecting carcinogens in the Ames test, the test substance is treated with
ground-up rat liver
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
Indirect selection
is necessary to isolate auxotrophic mutants
The enzymes of the mismatch DNA repair mechanism distinguish between the template strand and the newly synthesized strand by the presence of a _____ group on certain nucleobases of the template strand
methyl
DNA is protected from restriction enzymes by being
methylated
Sometimes the proofreading function of DNA polymerase misses errors in nucleotide incorporation. These errors are usually fixed by a mechanism called _____ repair
mismatch
The genes that vary considerably among strains of a species are called the _____
mobile gene pool
Mutations are rare because _____
most damage is repaired before it is passed on to progeny
The source of variation among microorganisms that were once identical is
mutation
Chemically mutagens that modify _____ increase the odds of incorrect nucleotide incorporation during DNA replication
nucleobases
The easiest way to detect if DNA transformation occurred in the lab is if _____ grow under selective conditions
only transformed cells
Genomic islands that encode disease-causing factors such as exotoxins, capsules, and adherence factors are called _____ islands
pathogenicity
To increase the proportion of auxotrophic mutants in a population of bacteria, one may use
penicillin enrichment
The _____ is the observed characteristics of an organism
phenotype
The properties of a cell that are determined by its DNA composition are its
phenotype
Colonies of the bacterium Serratia marcescens ar red when incubated at 22C but white when incubated at 37C. This is an example of
phenotypic change
In bacterial conjugation, a donor cell with an F _____ is considered F+
plasmid
A _____ mutation occurs if a single base pair is changed during DNA synthesis
point
The designation his- refers to
the genotype of bacteria that lack a functional gene for histidine synthesis AND bacteria that are auxotrophic for histidine
The diploid character of eukaryotic cells may mask the appearance of a mutation since
the matching chromosome may carry the correct version of the gene
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
Which of the following are sources of "naked" DNA?
-Secreted into the environment by bacteria -Lysed (burst) bacteria cells
Place the steps of F plasmid transfer in the correct order
1. F pilus makes contact with recipient cell 2. one strand of F plasmid is cut in origin or transfer 3. single strand of F plasmid is transferred to the recipient cell 4. complement of transferred strand is synthesized
Place the steps of DNA-mediated transformation into the correct order
1. double-stranded DNA molecule binds to surface receptor, 2. nucleases degrade one strand of double-stranded DNA at the cell surface, 3. single-stranded DNA enters 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
The material responsible for transformation was shown to be DNA by
Avery, Macleod, and McCarty
When an excision error produces a plasmid containing both chromosomal and F plasmid DNA, the resulting plasmid is called a _____ plasmid
F'
When integrated F plasmid DNA is excised from the chromosome, an excision error can result in the removal of chromosomal DNA along with the F plasmid DNA, creating a plasmid called _____
F'
_____ are circular pieces of bacterial DNA that do not usually encode information essential to the life of a cell
Plasmids
Some bacteria have a higher incidence rate of thymine dimer mutations following exposure to UV light than others. What might be going on here to lead to this outcome?
They may simply have a higher proportion of T nucleotides next to each other in their DNA than other bacteria, leading to more possible dimers being formed AND they may have a weaker expression of photo-reactivation enzymes, leading to the formation of more thymine dimers
_____ are DNA segments that increase the rate of mutations by inserting themselves into genes and inactivating them
Transposons
_____ are segments of DNA that can move from one location to another in a cell's genome
Transposons
Crown gall is caused by a prokaryote plasmid that can be expressed in plant cells.
True
DNA polymerase is able to proofread the DNA sequence
True
Each gene mutates at a characteristic frequency.
True
Because CRISPR systems involve bacteria using retained segments of DNA to identify and destroy future invading phage DNA, these systems are a form of _____
adaptive immunity
Chemicals called _____ add alkyl groups onto nucleobases, changing their base-pairing properties.
alkylating agents
Base _____ structurally resemble nuclebases and can be mistakenly incorporated into nucleotides and then into DNA
analogs
Many bacteria are able to recognize and destroy invading DNA. It is thought this ability evolved _____
as defenses against phages
A mutant that requires a growth factor is an _____
auxotroph
in replica plating, colonies that grow on the master plate but cannot grow on the glucose-salts plate are _____
auxotrophs
Modified nucleobases can result in _____ if they are not repaired before DNA replication occurs
base substitutions
Conjugation, DNA-mediated _____, and _____ are methods of horizontal gene transfer in bacteria
transformation; transduction
Variation in the color of corn kettles, as described by Dr. Barbara McClintock, is an example of the process called _____
transposition
Segments of DNA capable of moving from one area in the DNA to another are called
transposons
On which of the following DNA strands would UV radiation have the most effect?
AATTAGTTC
Which change in a gene's DNA sequence would have the least effect on the eventual amino acid sequence produced from it?
Addition or deletion of three consecutive nucleotides
You mix two bacterial stains in a tube of glucose-salts agar. One strain is His-, Val-, while the other strain is Trp-, Leu-. You previously showed that neither strains grows on glucose-salts agar. After incubating the tube, you plate a sample onto a new glucose-salts agar plate. Several new colonies grow. What do you know is TRUE about these colonies.
The bacteria in the colonies are His+, Val+, Trp+, Leu+
A bacterial strain is resistant to infection by a bacteriophage. which statement is FALSE
The bacterial host DNA is protected from restriction enzyme degradation by phosphorylation
DNase is added to a mixture of donor DNA and recipient. If the donor DNA is naked, what will happen?
The recipient will be unable to acquire DNA via transformation
_____ such as E. coli are an excellent model system for genetics studies because they can quickly grow to high densities, allowing us to screen for rare genetic events
bacteria
A bacterial cell described as _____ can take up DNA from the surrounding environment
competent
not all bacteria can take up DNA from the environment. Those that can are referred to as
competent
in bacteria, _____ refers to DNA transfer requiring cell to cell contact
conjugation
Mutants that can grow under conditions, in which the parent (wild type) cells cannot, are easily isolated by _____ selection
direct
Mutant cells in bacterial cultures can be isolated by _____ and _____ selection methods
direct and indirect
In conjugation, transformation, or transduction, the recipient bacteria is most likely to accept donor DNA
from the same species of bacteria
Bacteria that have properties of both the donor and recipient cells are the result of
genetic recombination
DNA repair mechanisms occur
in both eukaryotes and prokaryotes
In the Ames test, it is expected that a mutagen would _____ the reversion rate of a histidine-requiring auxotroph of Salmonella
increase
The clustered, regularly interspaced short palindromic repeats (CRISPR) system in bacterial cells has been called the "immune" system of bacteria. CRISPR protect bacteria from a repeat infection from the same phage because bacterial cells
integrate fragments from the phage DNA in their own chromosomes and target for destruction any DNA that contains the same fragments in the future
Chemical mutagens that squeeze between base pairs and induce frameshift mutations are called _____
intercalating agents
Among the easiest of the mutations to isolate are those which
involve haploid chromosomes AND involve antibiotic resistance
Genetic change in bacteria occurs through which two mechanisms?
-horizontal gene transfer -mutation
What are some of the disadvantages of the SOS DNA polymerase?
-it. can result in a lot of mutations in the DNA -it has no proofreading ability
Some prokaryotes are naturally competent _____
-only under specific conditions -all the time
A bacteriophage consists of what two major components?
-protein coat -DNA or RNA genome
