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