Lecture 12
This figure shows a cell with an integrated F plasmid. If this plasmid is incorrectly excised, the result could be an F plasmid that carries along a portion of the bacterial chromosome. Such a cell would then be called a(n) Blank 1 cell.
F'
After new virus particles have assembled in the bacterial host cell, they are usually ______.
released as a result of host cell lysis
Plasmids that encode resistance to a variety of antimicrobial agents and heavy metals are called Blank______ plasmids or factors
R
Why is horizontal gene transfer important?
It enables bacteria to respond and adapt to their environment much more rapidly by acquiring large DNA sequences from another bacterium
How many strands of donor DNA integrate into a recipient chromosome during transformation?
One
Which of the following plasmids are self-transmissible?
conjugative plasmids only
Conjugation in bacteria requires _____
contact between donor and recipient cell
The genes that are present in all strains of a given species are called the ______.
core genome
Transduction exists in two kinds. What are they?
generalized specialized
When describing conjugation in Gram-negative bacteria, a donor cell with an F ______ is considered F+, while that without this structure are termed F-.
plasmid
What is a prophage?
viral DNA that has been integrated into a bacterial chromosome
Although mobilizable plasmids encode an origin of transfer, they lack other genetic information required for transfer. Under what circumstances can a mobilizable plasmid be transferred to another bacterial cell?
when a conjugative plasmid is present in the same cell
Which mechanism of gene transfer involves the uptake of "naked" DNA by competent bacterial recipient cells?
Transformation
Cells that have the ability to take up DNA from the environment are called ______ cells.
competent
Which of the following are examples of mobile genetic elements?
plasmids genomic islands transposons phage DNA
How is horizontal gene transfer different from mutation?
Horizontal gene transfer, on the other hand, enables bacteria to respond and adapt to their environment much more rapidly by acquiring large DNA sequences from another bacterium in a single transfer
During bacterial conjugation, synthesis of a new strand of F plasmid DNA occurs in ____
both the donor and recipient
In bacteria, Blank 1 refers to DNA transfer requiring cell to cell contact.
Blank 1: conjugation
A(n) Blank 1 Blank 2 is a large segment of a cell's genome that has clearly originated in a different species
Blank 1: genomic Blank 2: island
The structure connecting these two cells is called an F Blank 1and is formed during the mechanism of DNA transfer called Blank 2
Blank 1: pilus Blank 2: conjugation
In generalized transduction, donor DNA is mistakenly packaged into a phage coat, forming a(n) Blank 1 particle.
Blank 1: transducing
In insertion sequences, the Blank 1 Blank 1 gene (the only gene) is flanked by Blank 2 repeats.
Blank 1: transposase Blank 2: inverted
In bacterial conjugation, all F+ donor cells are high frequency recombinant (Hfr) cells.
False (Reason: Although both types of donors have plasmid DNA, only the Hfr cell has the plasmid integrated into the chromosome.)
Plasmids are insertion sequences that can lead to changes in genotype within a cell or between cells.
False (Reason: Insertion sequences that can lead to changes in genotype within a cell or between cells are called transposons. Plasmids are small circular pieces of DNA.)
When an Hfr cell transfers chromosomal DNA to a recipient cell, it does not need to produce an F pilus.
False (Reason: Like F' cells, Hfr cells produce an F pilus, and the F plasmid DNA directs its transfer to the recipient cell.)
In E. coli, less than 50% of the genes are found in all strains. These conserved genes are called the Blank 1 genome
Blank 1: core
During Blank 1 recombination, a segment of DNA inserts into the cell's genome, a process that does not require a similar nucleotide sequence in the region of recombination.
Blank 1: nonhomologous or non-homologous
"Jumping genes," or Blank 1, can move within a cell without specificity as to where they ultimately insert
Blank 1: transposons
How is an F+ cell different from an Hfr cell?
F+ cells can transfer plasmids via a sex pilus. Unlike the F plasmid, chromosomal DNA is not a replicon so it must integrate into the chromosome of the recipient cell through homologous
Plasmids with a Blank 1 copy number occur in only one copy per cell, while those with a Blank 2 copy number are present in many copies per cell.
Blank 1: low Blank 2: high
When an excision errors produces a plasmid containing both chromosomal and F plasmid DNA, the resulting plasmid is called a(n) Blank 1 plasmid
Blank 1: F' or F prime
In the most thoroughly studied example of bacterial conjugation, the term Blank 1 designates a donor cell with an F plasmid, whereas those cells who lack the F plasmid are termed Blank 2.
Blank 1: F+, F plus, Fplus, or Hfr Blank 2: F-, F minus, or Fminus
Place the steps of F plasmid transfer in the correct order. Start with the earliest at the top.
1. F pilus makes contact with recipient cell. 2. One strand of F plasmid is cut in origin of transfer. 3. Single strand of F plasmid is transferred to the recipient cell. 4. Complement of the transferred strand is synthesized.
Briefly distinguish between transformation, transduction, and conjugation.
In transformation, a bacterium takes up a piece of DNA floating in its environment. In transduction, DNA is accidentally moved from one bacterium to another by a virus. In conjugation, DNA is transferred between bacteria through a tube between cells.
How does the CRISPR system work?
It maintains a historical record of phage infections and thereby become immune to subsequent infections by the same phages; the system also protects against other types of foreign DNA.
Please match the statements about plasmid properties with the correct definition.
Low copy number => Occur in one or a few copies per cell High copy number => Occur in many copies in a cell Narrow host range => Can replicate in only one species Broad host range => Can replicate in many different species
Once donor DNA is in a recipient cell, it integrates into that cell's chromosome by ______.
homologous recombination
Plasmids, transposons and phage DNA are all examples of _____
mobile genetic elements
Restriction-modification systems were discovered _____
while studying why certain bacterial strains are relatively resistant to phage infection
When bacteriophages replicate, phage components are synthesized in the host cell and assemble into new viruses ______.
within that cell before being released
Which mechanisms of horizontal gene transfer require homologous recombination?
All 3
Which of the following plasmids encodes all the necessary genetic information for transfer from one bacterial cell to another?
Conjugative plasmids only
Match each characteristic with the appropriate nucleic acid molecule.
Contains an origin of replication => both plasmids and chromosomes Made of double stranded RNA=> neither plasmids nor chromosomes Typically do not encode genes essential to the life of the cell => plasmids only Found in all eukaryotes and prokaryotes => chromosomes only
Which of the following can be found in a bacteriophage?
DNA or RNA genome protein coat
With respect to phage replication, what error results in generalized transduction? What error results in specialized transduction?
Specialized: A fragment of bacterial DNA is mistakenly substituted for phage DNA within the protein coat. Error results in wild-type phage DNA. Generalized: When a piece of bacterial DNA remains attached and a piece of phage DNA is left behind in the bacterial chromosome. The resulting lysogens also contain bacterial genes from the previously lysogenized cells.
What is the "transforming principle" in Griffith's experiments?
The principle was able to transform a non-pathogenic bacteria into a pathogenic strain
In conjugation in E. coli, an Hfr cell refers to ______
a cell in which the F plasmid has been integrated into the cell chromosome
Many bacteria are able to recognize and destroy invading DNA. It is thought this ability evolved ____
as a defense against phages
Which of the following are components of the simplest transposon, an insertion sequence?
inverted repeats transposase gene
The integration of a region of DNA into a segment that does not have extensive similarity in nucleotide sequence is called _____
non-homologous recombination
In transformation, only one daughter cell inherits donor DNA. This is because ______.
only a single strand of donor DNA integrates into the recipient chromosome
Neither strain A (His-/Trp-) nor strain B (Leu-/Thr-) can grow on minimal media on their own because they cannot synthesize the indicated amino acids. If the strains are mixed and then plated onto minimal media, any colonies that form ______.
should be a result of horizontal gene transfer
During conjugation, the F plasmid nucleic acid that transfers is __
single-stranded DNA
Chromosomal DNA is transferred with F plasmid DNA in an Hfr cell because ____
the plasmid DNA is integrated into the chromosome in these cells
In this diagram, step 5 was left out on purpose. You would expect it to show the formation of a ____
transducing particle
When horizontal gene transfer occurs between a donor and recipient cells, the resulting cells are called Blank 1
Blank 1: recombinants
The F or fertility plasmid contains genes that are required for bacterial _____
conjugation
This figure depicts the interconversion between an F+ cell and a(n) Blank 1 cell.
Blank 1: Hfr
An origin of transfer is encoded by ____
both conjugative and mobilizable plasmids
Place the steps of DNA-mediated transformation into the correct order. Start with the earliest at the top.
1. Double-stranded DNA molecule binds to surface receptor. 2. Nucleases at the cell surface degrade one strand of the DNA; the other strand enters the cell. 3. Single-stranded DNA integrates into genome after entering the cell. 4. Strand being replaced by donor DNA is degraded.
Which of the following are characteristics of recombinants?
They result from horizontal gene transfer. The have properties of both donor and recipient cells.
_______ is the transfer of bacterial DNA from a donor to recipient via a bacteriophage.
Transduction
Which of the following statements about transformation is correct?
Transformation is the uptake of naked DNA from the environment.
Blank 1 transduction results from a packaging error during the virus replication cycle, when a piece of bacterial DNA is included in the new virus particle.
Blank 1: Generalized
Blank 1 are circular pieces of bacterial DNA that do not usually encode information essential to the life of a cell.
Blank 1: Plasmids
A bacteriophage consists of a genome made up of DNA or Blank 1 surrounded by a coat made up of Blank 2
Blank 1: RNA Blank 2: protein, polypeptides, or proteins
A(n) Blank 1 is a virus that infects bacteria, and some can transfer bacterial genes from a donor cell to a recipient cell.
Blank 1: bacteriophage or phage
A plasmid that can directs its own transfer from donor to recipient cells is called a(n) Blank 1 plasmid.
Blank 1: conjugative
There are two types of transduction: Blank 1, which transfers any genes of the donor cell, and Blank 2, which transfers only a few specific genes.
Blank 1: generalized Blank 2: specialized
When two bacterial strains that are His-/Trp- (require his and trp for growth) and Leu-/Thr- (require leu and thr for growth) are mixed together and plated on minimal media, any colonies that form are likely due to one strain acquiring genes from another strain. This is called Blank 1 gene transfer.
Blank 1: horizontal
Why won't the fragment of DNA shown in Figure 8.18a replicate in the cell?
Because it doesn't have an origin of replication; the DNA fragment has to be integrated into a chromosome in order to be maintained.
In prokaryotes, genes can be transferred from a donor to a recipient via three different mechanisms: Blank 1,Blank 2, and Blank 3.
Blank 1: transformation, bacterial transformation, or DNA-mediated transformation Blank 2: transduction Blank 3: conjugation
