Module 4b part 2
A key component of the SOS response is the destruction of a transcriptional repressor protein called _______.
LexA
Which approach would be used to screen for revertants from a lysine auxotroph?
Plate a large number of lysine auxotrophs on a minimal medium lacking lysine.
When DNA damage is so great that DNA synthesis stops, a control system called the ________ response occurs
SOS
True or false: A mutation can prevent a gene from being expressed, even if the coding sequence is completely unchanged.
True
A suppressor mutation, which returns a mutant back to its wild-type phenotype, occurs at ______the first mutation.
a different site from
Alternative forms of a gene are called
allele
The lambda phage of E. coli is a temperate bacteriophage, meaning that it _________.
can insert its genome into the host chromosome
In bacteria, conjugation refers to the transfer of DNA by ________.
cell to cell contact
In bacteria, conjugation refers to the transfer of DNA by Blank______.
cell-to-cell contact
Antibiotic resistance genes like those found on R plasmids often code for enzymes that ________.
destroy or modify antibiotics
Spontaneous mutations can occur when a nitrogenous base shifts to a different isomer, also called a(n) Blank
tautomeric form
The process of taking up DNA from the surroundings, and maintenance of the DNA in a heritable form, is called
transformation
DNA segments that can repeatedly insert into one or more sites or into one or more genomes are called
transposable genetic
The most prevalent form of a gene, and its associated phenotype, is called the ____ type
wild
A wild-type chemoorganotroph like E. coli able to grow on a minimal medium containing only salts and a carbon source is known as a(n) ___________. These wild-type strains may give rise to mutants incapable of survival without additional nutrients, like a particular amino acid.
Prototroph
Which three statements regarding homologous recombination are correct?
RecA protein is involved. Similar or identical DNA strands are broken and reunited. It is the most common mechanism of DNA recombination.
Which example of a missense mutation in a protein-encoding gene would most likely be a neutral mutation?
Replacement of a polar amino acid with another polar amino acid at the protein's surface
Match each protein or protein complex involved in mismatch DNA repair with its function.
Scan newly replicated DNA for mismatchesSeparate the parental and new DNA strands around a mismatchProtect the methylated (parental) DNA strandSynthesize DNA complementary to the methylated (parental) strand
Some instances of antibiotic resistance occur by spontaneous chromosomal mutation. In these cases, the mutation results in
a change in the drug target such that the drug can no longer bind
A genetic selection differs from a genetic screen in that __________.
a genetic selection adjusts the environment so that only mutants of the desired phenotype can grow
Select two examples of mutations that affect regulatory sequences of microbial genes.
a mutation in a promoter so that RNA polymerase cannot bind a mutation in the lac operator so the lac repressor cannot bind
In simple transposition, a mobile genetic element ________.
excises from one location and inserts in a different location in the same genome
Which type of DNA repair corrects damage (e.g., thymine dimers) that causes distortions in the DNA double helix?
excision repair
William Hayes' 1952 experiments demonstrated that conjugation is unidirectional and identified strains he named F+ and F-. The "F" stands for
fertile
A mutation that leads to a change from wild type to a mutant form is called a(n) ______ mutation
forward
Mutations that arise from the insertion or deletion of 1 or 2 base pairs within the coding region of a gene are called _______ mutations
frameshift
The major conclusion of Hayes' 1952 experiments, which demonstrated the existence of F+ and F- strains, was that __________.
he major conclusion of Hayes' 1952 experiments, which demonstrated the existence of F+ and F- strains, was that
Hfr strains of bacteria are so named because they undergo a __________ (high/low) frequency of ___________.
high, recombinants
The most common type of DNA recombination (e.g., during meiosis or bacterial horizontal gene transfer) is _________ recombination between similar or identical DNA strands.
homologous
Drug resistance often arises when bacteria gain new properties by acquiring genes from other bacteria. This process is known as _______ gene transfer.
horizontal
Drug resistance often arises when bacteria gain new properties by acquiring genes from other bacteria in the process known as
horizontal gene transfer
In this diagram illustrating F-factor-mediated conjugation, the arrow points to the _______.
sex pilus
Point mutations that change the nucleotide sequence of a codon but do not change the amino acid encoded by that codon are called ________ mutations
silent
Since the second amino acid is threonine (thr) in both the original and mutant sequences, the type of mutation illustrated here is a(n) ____ mutation
silent
A mutation that caused the codon CGU to change to CGC, which does not affect the amino acid encoded, could be described by which two of these terms?
silent, point
Select the best definition of mobile genetic elements.
specific DNA segments that can repeatedly insert into one or more sites or into one or more genomes
Mutations that result from head-on collisions between the replisome and RNA polymerase are considered to be ______ mutations
spontaneous
Mutations that result from head-on collisions between the replisome and RNA polymerase are considered to be ______ mutations.
spontaneous
Some instances of antibiotic resistance result in modification of the antibiotic target such that it is no longer inhibited by the antibiotic. Such events generally result from
spontaneous chromosomal mutations
ome instances of antibiotic resistance result in modification of the antibiotic target such that it is no longer inhibited by the antibiotic. Such events generally result from ______.
spontaneous chromosomal mutations
Which two of these missense mutations would be predicted to have the most severe effects on the function of the protein encoded by the mutated gene?
substitution of an amino acid located at the active site of an enzyme replacement of a nonpolar amino acid with a polar amino acid
A second mutation that occurs at a different site from the first mutation, and which returns the mutant back to the wild-type phenotype, is a(n) _____ mutation
suppressor
A bacteriophage that can insert its genome into a bacterial chromosome is known as a(n) _________ bacteriophage.
temperate
Mismatched DNA bases in the double helix are repaired by ________.
the mismatch repair system that eliminates the daughter strand and re-synthesizes it on the parental strand template
When the mismatch repair system of E. coli detects mismatched bases, it is able to determine the strand that needs repair, because______ is methylated
the old strand
In bacterial genetics, transformation is _______.
the uptake of free DNA by a bacterial cell
Order these steps in simple transposition, with the first event at the top.
- Transposase excises the mobile genetic element - Transposase identifies a new insertion site and cleaves the strands 5 to 0 bases apart - Transposase ligates the mobile genetic element DNA with the host insertion site - Host enzymes fill in gaps, resulting in a 5 to 9 base duplication at either end of the mobile genetic element
Which three of the following are correct descriptions of plasmids?
1) They can exist independently of host chomosomes.2) Some can integrate into host chromosomes.3) They are small, double-stranded DNA molecules.
Which two of these bacterial mutants could be selected by exposing them to a particular stress condition and looking for growth?
A mutant resistant to a particular antibiotic A mutant resistant to bacteriophage infection
Which three statements apply to an F' plasmid?
An F' plasmid has been excised from a bacterial chromosome. An F' plasmid includes some chromosomal genes. An F' plasmid is an erroneously excised plasmid.
Frameshift mutation
Changes the DNA sequence by inserting or deleting a few bases to generate a polypeptide from the wrong reading frame
Missense mutation
Changes the DNA sequence to a codon that specifies a different amino acid from wild type
Silent mutation
Changes the DNA sequence to a codon that specifies the same amino acid as wild type
Nonsense mutation
Changes the DNA sequence to a stop codon to generate a shorter polypeptide
Although mismatch DNA repair and nucleotide excision repair address different types of lesions, they share three enzymes, _________, _______, and _________.
DNA polymerase I DNA ligase UvrD helicase
Which three of these statements about nonsense mutations are correct?
Effects range from mild to complete loss of normal gene function. By definition, they always produce stop codons. They cause the early termination of translation.
Which three of these statements about nonsense mutations are correct?
Effects range from mild to complete loss of normal gene function.They cause the early termination of translation.By definition, they always produce stop codons.
Which of these is the defining characteristic of an Hfr strain?
F plasmid integrated into the host chromosome
The major mechanism by which bacteria and archaea evolve (acquire novel genes) is
Horizontal gene transfer
Which two statements concerning horizontal gene transfer are correct?
Horizontal gene transfer helps microbes survive environmental stress. Horizontal gene transfer is common among microbes sharing a habitat.
Which phrase best describes the form of a gene designated the "wild type?"
The more prevalent form of the gene
Which of these descriptions applies to prototrophs?
They are chemoorganotrophs able to grow on a minimal medium containing only salts and a carbon source.
Which two of these descriptions apply to auxotrophs?
They have a conditional phenotype. They are unable to grow on medium lacking a particular molecule, where the wild-type strain could grow.
Transduction, the horizontal transfer of genes by virus particles, occurs through _________.
errors in the virus life cycle
In simple transposition, a mobile genetic element
excises from one location and inserts in a different location in the same genome
Transposases are enzymes that recognize the ends of a(n) _____.
insertion sequence
A resistance mutant may have acquired resistance to which three of the following?
pathogen antibiotic chemical
The structure used to establish physical contact between an F+ and F- cell is called a sex
pilus
Which two statements concerning horizontal gene transfer are correct?
plasmids
Silent, missense, nonsense, and frameshift are all common types of __________ mutations
point
The type of mutation that affects only a single base pair at a given DNA location is called a(n) ____ mutation
point
The genome of a temperate bacteriophage that has been inserted into a bacterial genome is called a(n)
prophage
A mutant that can survive exposure to some pathogen, chemical, or antibiotic, is a(n) ____ mutant
resistant
An allele is most likely to persist in a population if it confers a survival advantage under ______pressure.
selective
Which three types of mutations are classified as reversion mutations?
- A second mutation creates a codon that replaces the wild type amino acid with a similar amino acid. - A second mutation that restores the original wild-type sequence. - A second mutation that creates a different codon that codes for the wild type amino acid.
Which two statements correctly describe missense mutations?
- Effects range from no change to complete loss of normal gene function. - They are a single base substitution that changes a codon for one amino acid into a codon for a different amino acid.
Mismatch repair Nucleotide excision repair Base excision repair
- The strand lacking methylation is removed. - matches Choice The strand with a DNA distortion is removed. - The strand with an apurinic or apyridinic site is removed.
Which two of these statements are correct about frameshift mutations?
- They usually yield mutant phenotypes. - They usually result in the synthesis of nonfunctional proteins.
By using a mutagen, the mutation rate can be increased to one mutant cell out of approximately
1,000 to 1,000,000
Under normal growth conditions, the rate of naturally-occurring mutant cells is one mutant cell out of approximately ______ cells.
10^7 to 10^11
Match each type of excision repair with the type of lesion that it repairs.
Nucleotide excision repair ----> thymine dimer Base excision repair ---> apurinic or apyrimidinic site
An F plasmid that has been excised from a bacterial chromosome, and includes some chromosomal genes, is called a(n) ______.
F' plasmid
An F plasmid that has been excised from a bacterial chromosome, and includes some chromosomal genes, is called a(n) _______.
F' plasmid
Which statement regarding viruses and their life cycles is false?
Viruses can replicate either within a host cell or autonomously.
Which of the following statements about viruses and transduction is false?
Viruses escaping a bacterium can find a new host cell and move genes to an archaeon.
Vertical gene transfer is observed in _________.
all organisms
An organism with a mutation that affects its ability to synthesize a biochemical essential for its growth is known as a(n)
auxotroph
Base analogues, DNA-modifying agents, and intercalating agents are three types of ____ mutagens
chemical
Mutations that are expressed only under certain environmental conditions are called _____ mutations
conditional
The image shows horizontal transfer of bacterial DNA by the process known as _______.
conjugation
Which two of the following are types of DNA damage that are corrected by nucleotide excision repair?
distortions in the double helix thymine dimers
In mismatch repair, the DNA strand to be removed is targeted because it __________.
does not have the parental methylation pattern
DNA proofreading occurs
during DNA replication, before the next nucleotide is added
Select three examples of chemical mutagens.
intercalating agents, base analogs, DNA-modifying agents
In a genetic selection, the wild type organisms are _____, whereas in a genetic screen, the wild type organisms are ______.
killed / alive
A bacterium that has been infected by a temperate bacteriophage, and is therefore carrying a prophage, is known as a(n)
lysogen
A bacterium that has been infected by a temperate bacteriophage, and is therefore carrying a prophage, is known as a(n) _______.
lysogen
Bacteriophages that lyse their host cells after completing one cycle of replication and assembly are called
lytic
Considering the change in amino acid, the mutation illustrated in these sequences is a(n) ______ mutation
missense
Point mutations in a single base that result in a change to the amino acid encoded are called ________ mutations
missense
Select three synonyms for genetic elements that can move around genomes by transposition.
mobile genetic elements transposable elements jumping genes
Possible causes of spontaneous mutation include
mobile genetic elements, spontaneous lesions in DNA, errors in DNA replication
Transition mutations, which result in purine for purine substitution or pyrimidine for pyrimidine substitution, are ______ common than transversion mutations.
more
Silent mutations have no change in phenotype because
more than one codon exists for most amino acids
Silent mutations have no change in phenotype because _______.
more than one codon exists for most amino acids
The T4 phage of E. coli is a virulent bacteriophage, meaning that it _______.
multiplies in and lyses its host after infection
The general term for heritable changes in DNA sequence is________
mutation
A missense mutation that has little to no effect on the activity of a gene product is called a(n) ______ mutation
neutral
A tautomeric form is an isomer of a nucleotide in which the ________ is changed
nitrogenous base
Point mutations that create a stop codon within a reading frame are called ______ mutations
nonsense
Point mutations that create a stop codon within a reading frame are called _______ mutations
nonsense
Nucleotide substitutions that result in purine for purine or pyrimidine for pyrimidine mutations are known as ___________ mutations.
transition
The movement of a mobile genetic element is called
transposition
The mismatch repair system of E. coli is able to detect mismatched bases because, for a short time, newly synthesized DNA strands are _______.
unmethlyated
This diagram illustrates binary fission, a type of
vertical