Microbiology chapter 16: mechanisms of genetic variation
Place these steps in natural bacterial transformation in order, with the earliest event at the top
1) Double-stranded DNA is brought to the plasma membrane surface 2) One DNA strand is degraded as the other strand enters the cell 3) Single-stranded DNA interacts with RecA 4) Single-stranded DNA integrates into the chromosome
Arrange these steps in rolling-circle replication in order. Place the initial event at the top.
1) one strand of circular DNA is nicked 2) the 3' hydroxyl end of DNA is lengthened 3) the 5' end of DNA is displaced from the template 4) complementary DNA is synthesized
Arrange these events involved in F+ X F- mating in order. Place the earliest event at the top.
1) sex pilus on F+ cell establishes contact with F- cell 2) sex pilus retracts, pulling the cells close together 3) F+ cell assembles type IV secretion apparatus 4) F factor undergoes rolling circle replication
Match each mechanism of bacterial horizontal gene transfer with its definition.
Conjugation ~ DNA transfer by direct physical contact of cells Transduction ~ transport of DNA by viruses Transformation ~ transfer of naked DNA fragments
The E. coli F factor carries genes that are responsible for ______ and _____
DNA transfer and formation of the sex pili
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, and 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
Prior to Hfr conjugation, the cell that will receive DNA is classified as
F-
The major difference between natural transformation in Gram-positive vs. Gram-negative bacteria is that
Gram-negative bacteria must move DNA across an outer membrane
Which two statements concerning horizontal gene transfer are correct?
Horizontal gene transfer is common among microbes sharing a habitat and Horizontal gene transfer helps microbes survive environmental stress.
Which three statements regarding homologous recombination are correct?
It is the most common mechanism of DNA recombination, similar or identical DNA strands are broken and reunited, and RecA protein is involved
Point mutations in a single base that result in a change to the amino acid encoded are called _____ mutations.
Missense
Which of the following statements regarding transformation is false?
Natural transformation cannot be studied in the laboratory.
Which statement regarding transformation is false?
Natural transformation occurs in bacteria but not in archaea or eukaryotes.
What effect would you expect from a mutation that deleted the -35 region of the lac operon promoter?
No expression regardless of the carbon source available
Which process of gene transfer is shown in the diagram? (circle)
Rolling-circle replication
Which of the following statements regarding the E. coli F factor is false?
The F factor is double-stranded circular DNA of about 5,000 base pairs (should be 100,000 bp)
How do intercalating agents induce DNA mutations?
They insert between stacked bases of the helix.
Which two of these statements are correct about frameshift mutations?
They usually yield mutant phenotypes and They usually result in the synthesis of nonfunctional proteins.
A key event that occurs in specialized transduction, but not in generalized transduction, is
activation of a prophage to its lytic cycle
Vertical gene transfer is observed in
all organisms
Following an F+ X F- conjugation
both cells contain a copy of the F factor
When DNA in the environment contacts the surface of a competent cell, it is
bound and imported to the cytoplasm
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
Mutations in a promoter region that affect the ability of RNA polymerase to initiate transcription include ______ and ___
changing the sequence of the -35 region and changing the spacing between -35 and -10 regions
The image shows horizontal transfer of bacterial DNA by the process known as
conjugation
Ultraviolet radiation may generate a thymine dimer, which is
covalent bonding between two adjacent thymines in a single strand
Which two statements correctly describe missense mutations?
effect range from no change to complete loss of normal gene function and they are a single base substitution that changes a codon for one amino acid into a codon for a different amino acid
Which three of these are required for a successful F+ X F- mating
extrachromosomal F Factor, type IV secretion apparatus, and sex pilus
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
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
Mechanisms that result in the transfer of genes from one independent, mature organism to another are collectively called ____ gene transfer.
horizontal
The major mechanism by which bacteria and archaea evolve (acquire novel genes) is
horizontal gene transfer
Mutations that result from exposure to a physical or chemical agent (mutagen) are known as ______ mutations.
induced
Chemical mutagens that are planar molecules and insert themselves between stacked bases of the DNA helix are called _____ agents.
intercalating
In generalized transduction, the fragment of the host genome mistakenly packaged is chosen because
it is about the same size as the phage genome
Following transfer of the single-stranded F factor DNA into the recipient cell,
its complementary strand is synthesized
The mutation illustrated in these sequences is a ____ mutation. (single nucleotide switch that results in a different amino acid)
missense
Silent mutations have no change in phenotype because
more than one codon exists for most amino acids
Point mutations that create a stop codon within a reading frame are called _____ mutations.
nonsense
Silent, missense, nonsense, and frameshift are all common types of ____ mutations.
point
Organisms produced when nucleic acids are rearranged or combined to produce a new genotype are called
recombinants
The process in which nucleic acids are rearranged or combined to produce a new genotype is called
recombination
A mutation in the operator site of the lac operon that prevents the lac repressor protein from binding, is considered a mutation in a(n)
regulatory sequence
The type of mutation in this sequence is a ____ mutation. (one nucleotide replacement, no amino acid change)
silent
Match the type of mutation with the resulting protein sequence. Instructions
silent mutation ~ Changes the DNA sequence to a codon that specifies the same amino acid as wild type Missense mutation ~ Changes the DNA sequence to a codon that specifies a different amino acid from wild type Nonsense mutation ~ Changes the DNA sequence to a stop codon to generate a shorter polypeptide Frameshift mutation ~ Changes the DNA sequence by inserting or deleting a few bases to generate a polypeptide from the wrong reading frame
The amount of bacterial DNA that can be transferred by generalized transduction depends mainly on the
size of the viral capsid
Which type of mutagenic event is depicted in the diagram?
slippage leading to a deletion
What type of mutagenic event is illustrated in this diagram?(add)
slippage leading to an insertion
The transfer of specific chromosomal DNA following induction of a prophage is called _____ transduction.
specialized
Mutations that arise in the absence of any added agent are ____ mutations.
spontaneous
Mutations that result from head-on collisions between the replisome and RNA polymerase are considered to be ______ mutations.
spontaneous
Possible causes of spontaneous mutation include
spontaneous lesions in DNA, errors in DNA replication, mobile genetic elements
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 and replacement of a nonpolar amino acid with a polar amino acid.
If a bacterial cell is competent, that means it can
take up DNA and become transformed
A bacteriophage that can insert its genome into a bacterial chromosome is known as a(n) _____ bacteriophage.
temperate
After Hfr conjugation, the recipient cell usually remains F- because
the connection between cells breaks before the complete F factor is transferred.
Which phrase best describes the form of a gene designated the "wild type?"
the more prevalent form of the gene
What would be the effect of a mutation in the operator sequence of the lac operon, so that the lac repressor protein could not bind?
the operon would be continuously transcribed
UV radiation can cause mutations by inducing
thymine dimers
Select the three major mechanisms of horizontal gene transfer in bacteria.
transduction, transformation, and conjugation
Select the best definition of horizontal gene transfer.
transfer of genes from one independent, mature organism to another
This diagram illustrates binary fission, a type of gene transfer commonly observed in bacteria and archaea.
vertical
The most prevalent form of a gene, and its associated phenotype, is called the ____ type.
wild