Mastering Microbiology Exam 3

Two double-stranded DNA molecules, each consisting of one parental strand and one daughter strand.
What are the products of semiconservative replication for a double-stranded DNA molecule?
An organism must copy its DNA to pass genetic information to its offspring.
Why is DNA replication essential for a cell?
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It serves as the template for DNA replication.
What is the function of the parental DNA in replication?
DNA helicase
Which enzyme breaks the hydrogen bonds during replication?
They bind to the single-stranded DNA.
How do stabilizing proteins work on the DNA?
It moves ahead of the newly synthesized DNA.
In which direction does the replication fork move?
Stabilizing proteins
What ensures that the single strands of DNA do not come back together?
DNA is flexible.
What characteristic of DNA allows two connected DNA polymerases to synthesize both the leading and lagging strands?
They link the leading strand DNA polymerase and the lagging strand DNA polymerase together.
What is the function of the connector proteins?
Leading strand
Which DNA strand is synthesized continuously?
Lagging strand, DNA ligase, and discontinuous
Which of the following are terms associated with Okazaki fragments?
The synthesis is moving in the opposite direction from the replication fork.
Why is the DNA synthesis of the lagging strand considered discontinuous?
The promoter
What is the initial target of RNA polymerase?
template strand of DNA.
RNA polymerase is guided by the
stem loop.
RNA that has hydrogen bonded to itself forms a
Increase the level of transcription
How would one increase the concentration of a particular polypeptide in a cell?
5′ to 3′
During elongation, how is the RNA synthesized?
A molecule of RNA is formed based on the sequence of nucleotides in DNA.
Which of the following events occurs during transcription?
mRNA moves from the nucleus to the cytoplasm following RNA processing.
Which of the following is a correct statement about mRNA?
ribosomes in the cell cytoplasm
The site of translation is
Which one of the following does not play a role in translation?
mRNA attaches to the small subunit of a ribosome.
Which of the following does not occur during RNA processing?
As shown in the animation, the start codon also codes for which amino acid?
A stop codon would be introduced prematurely.
What would happen if the mRNA codon that coded for Cys was mutated in the third position from a U to an A?
nonionizing radiation.
Thymine dimers result from
Which of the following might result in a frameshift mutation?
It can replace the base thymine, and can base pair with guanine rather than adenine.
Which of the following describes how 5-bromouracil might create a mutation?
increase the likelihood of mutations in DNA.
can alter nitrogenous bases of DNA, resulting in incorrect base pairing.
A nucleotide-altering chemical
One in every billion nucleotides replicated.
What is considered to be the average natural mutation rate that occurs during DNA replication?
silent mutation.
A mutation that affects the genotype of the organism but not the phenotype is called a
frameshift mutation.
A base insertion or deletion in the translated region of the gene may lead to
nonsense mutation.
A base substitution that changes a codon coding for an amino acid to a stop codon is called a
One out of every three mutations
How frequently do silent mutations occur?
The structural genes
Which of the following genetic elements is transcribed into a single mRNA?
Repressible operons
Which operons are always transcribed unless deactivated?
Inducible operons
Which operons are never transcribed unless activated?
The operator
According to the animation, where on the DNA strand does a repressor bind?
is a cell that receives DNA from an outside source and incorporates it into its own.
A recombinant cell
Transfer of DNA between organisms of the same generation
What is the hallmark of all horizontal gene transfers?
Transduction, conjugation, and transformation
Which of the following is an example of horizontal gene transfer in bacteria?
Conjugation does not result in the formation of new offspring
Bacterial conjugation is often referred to as bacterial sex. Why is this term inaccurate?
The cells must come into contact with each other.
What must occur for bacterial conjugation to take place?
Conjugation is a process of bacterial reproduction.
Which statement about conjugation is false?
A bacterial plasmid
Based on the animation, what is transferred during bacterial conjugation?
Transduction transfers DNA from the chromosome of one cell to another.
What is unique about transduction compared to normal bacteriophage infection?
Generalized transduction is initiated during lytic cycle of a virulent bacteriophage; specialized transduction is initiated during the lysogenic cycle of a temperate bacteriophage.
How is generalized transduction different from specialized transduction?
contains fragments of the host chromosome instead of the viral genome.
A transducing phage
the DNA from the previous host can recombine with the new host chromosome.
When a transducing phage interacts with a new host cell,
can take up DNA from their surrounding environment and integrate it into their own chromosomes by recombination.
Competent cells are cells that
stay healthy, because their immune systems can kill this strain easily.
Mice that are injected with only the R strain of Streptococcus pneumoniae
The cells have a capsule.
What characteristic of the S strain allows it to evade the immune system of the mice?
The R strain picked up the S strain DNA, enabling it to produce a capsule.
What most likely explains the recovery of live S strain cells from a mouse injected with heat-killed S strain mixed with live R strain cells?
S strain cells are isolated from the blood of mice infected with heat-killed S strains and live R strains.
Which finding is most surprising from Griffith’s experiments?
They provide a 3′ end for the DNA polymerase.
What is the function of the primers in PCR?
5′ to 3′
In which direction does DNA polymerase synthesize the new DNA strand?
Deoxyribonucleoside triphosphates
What provides the energy for DNA polymerization in a PCR reaction?
It can withstand the high temperatures associated with PCR.
Why is DNA polymerase from Thermus aquaticus ideal for PCR?
72 degrees
What is the temperature used for the extension step?
The high heat of the denaturation step breaks the hydrogen bonds between the two strands.
How do the strands separate during PCR?
The machine that controls the heat of the reaction, cycling between the different temperatures of the different steps during PCR
What is a thermocycler?
94 °C, 60 °C, 72 °C
What is the sequence of the temperatures of a typical PCR reaction?
They cut DNA at sites, called recognition sites, that have specific nucleotide sequences.
How do restriction enzymes cut DNA sequences?
To insert a desirable gene, remove an undesirable gene, or replace a defective gene with a functioning gene
In general, how might recombinant DNA technology be used to prevent a genetic disorder caused by a mutation in a single gene?
DNA ligase
Which of the following attaches the target gene to a desired location?
It can be copied, transcribed, and translated into a desired protein.
Why would a recombinant DNA molecule be inserted into a host cell?
a culture of genetically identical cells
Which of the following best describes a clone in the context of genetic modification procedures?
Cells usually won’t copy an isolated gene sequence.
Which of the following best describes why a vector is used in genetic modification procedures?
Producing a clone generates many copies of the gene of interest.
Recombinant DNA techniques typically involve generating a clone. Why?
Bacteria now produce hGH.
Which of the following best describes how recombinant DNA technology currently helps patients who do NOT produce adequate amounts of growth hormone (hGH)—a condition that otherwise leads to stunted growth?
Chemotherapeutic agents should act against the pathogen and not the host.
What is meant by selective toxicity?
Humans and other animal hosts lack peptidoglycan cell walls.
Why are chemotherapeutic agents that work on the peptidoglycan cell wall of bacteria a good choice of drug?
It can also damage living human cell membranes, but the drug is safely used on the skin, where the outer layers of cells are dead.
Why is polymyxin only used on the skin?
DNA gyrase
Quinolones and fluoroquinolones act against what bacterial target?
Viruses depend on the host cell’s machinery, so it is hard to find a viral target that would leave the host cell unaffected.
Why is it difficult to find good chemotherapeutic agents against viruses?
Which antibiotic is overcome by beta-lactamases?
Resistant bacteria can have more efflux pumps, and can have less specific efflux pumps.
How might efflux pumps increase antibiotic resistance in bacteria?
Bacteria that are resistant to sulfonamide have enzymes that have a greater affinity for what?
Penicillin disrupts the cell wall, which is located outside of the cell membrane.
Why would an efflux pump for penicillin located on a bacterial cell membrane not be effective at providing resistance to the drug?
Efflux pumps, beta-lactamases, and modification of porins all utilize membrane transport proteins.
Membrane transport proteins are required for which mode(s) of antibiotic resistance?
The bacterium is neither killed nor inhibited by the antibiotic.
What is meant when a bacterium is said to become “resistant” to an antibiotic?
the drug will kill or inhibit the growth of all of the sensitive bacterial cells
When a patient is treated with antibiotics, __________.
The process of acquiring antibiotic resistance by means of bacteriophage activity is called
Silent mutation
Which of the following mutations would not result in antibiotic resistance?
bacterial conjugation.
R-plasmids are most likely acquired via

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