Microbiology (Bio 261) Chapter 10
What attaches the target gene to a desired location?
DNA ligase
The killing of cells by UV irradiation involves
formation of pyrimidine dimers. (Thymine and Adenine are pyrimidine)
A new chemotherapeutic agent is developed that alters the structure of all thymines in DNA. These thymines are then misread during the production of mRNA. Which of the following could NOT result from this type of mutation? nonsense, missense, frameshift, silent
frameshift
What type of mutation can change all subsequent amino acids following it?
frameshift
Ethidium bromide used in labs can result in _________________.
frameshift mutations via insertion or deletion of nucleotides.
What typically results from conjugation between an Hfr cell and an F- cell?
one Hfr cell and one F- cell
Which repair mechanism(s) requires assistance from DNA polymerase to make the correction?
excision-repair mechanism AND mismatch-repair mechanism
Which transduction is initiated during the lysogenic cycle of a temperate bacteriophage?
Specialized transduction (the donor DNA is a very specific part of the bacterial chromosome adjacent to the prophage)
Most plasmids are linear rather than circle. (true/false)
false
The words donor cell and recombinant cell can be used to describe the newly infected host of a specialized transducing bacteriophage (true/false)
false. it is not the donor cell. It can be called both the recipient cell and the recombinant cell.
When a gene mutation results in an amino acid change, it is called a __________ mutation.
missense mutation. (the mutated gene sequence codes for a different amino acid then what it was supposed to)
The genetic code is degenerate. Which of the following answers describes an example of the degenerate nature of the code? (define degenerate)
AUU, AUC, and AUA all code for Ile
Which of the following is a characteristic of an F+ cell?
Ability to synthesize sex pili, presence of a fertility factor, and ability to mate with an F- cell.
Damaged DNA can repaired by _________ enzymes that cut out the damaged DNA often along with nucleotides on either side the mutation. DNA polymerase can then fill in the gap.
excision repair enzymes
Chemical mutagens that cause small insertions or deletions of nucleotide base pairs.
frameshift mutagens. (The insertions and deletions may lead to frameshift mutations)
deletion mutations, insertion mutations, and substitution mutations are considered ______________ and occur when nucleotides are inserted into or removed from the DNA sequence.
frameshift mutations
The two types of transduction are:
generalized transduction and specialized transduction
F+ strains of Escherichia coli
have the F factor as a plasmid.
What does Hfr stand for?
high frequency of recombination
What happen to mice that are injected with only the R strain of Streptococcus pneumoniae
they stay healthy, because their immune systems can kill this strain easily.
Point mutations can be classified by _________ and __________.
Change in DNA sequence/ Effect on amino acid sequence
Why does conjugation between an Hfr strain and an F- strain not result in two Hfr strains?
Conjugation is typically disrupted before the fertility factor can be transferred.
In recombinant DNA technology, what is used to cut DNA at specific sequences?
restriction enzymes
Unlike S strains, R strains do not produce a capsule and are unable to cause disease in mice. (true/false)
true
auxotrophs need additional nutrients that the normal strain does not, whereas a prototroph can synthesize all the compounds needed for growth. (auxotrophy and prototrophy are opposites) true/false
true
mutagens increase the chance of error occurring in DNA replication. (true/false)
true
simple transposons which only contain only the essential elements for transposition (true/false)
true
Following conjugation between a donor and a recipient, what cell types are present?
two F+
How frequently does an error occur in DNA replication in the absence of a mutagen?
1 in every 1 billion
the simplest transposons are called _________.
insertion sequences
__________ convert purines to pyrimidines, or vice versa.
Transversions
Which of the following might result in a frameshift mutation? Nitrous acid 5-bromouracil Benzopyrene
benzopyrene
When a transducing phage interacts with a new host cell,
the DNA from the previous host can recombine with the new host chromosome
What is packaged by the bacteriophage during specialized transduction?
the phage DNA with some of the host DNA
How long does it take an Hfr strain of E. coli to transfer its complete chromosome?
100 minutes
What does it mean for a genetic code to be degenerate?
A single amino acid may be codes for by more than one codon.
The process of generalized transduction ___________. a.) requires a lytic bacteriophage. b.) utilizes any fragment of the bacterial chromosome. c.) results from sloppy packaging of DNA by bacteriophage. d.) all of the above e.) none of the above
All of the above
Missense mutations, nonsense mutations, and silent mutations are collectively called ___________ and occur when a single nucleotide replaces another in the DNA sequence.
Base substitution mutations
What is required by an F- cell to become an F+ cell?
F plasmid
What is the key difference between donor cells and recipient cells?
F plasmid
Why are F- cells unable to spread the fertility factor?
F- cells rarely receive a complete copy of the fertility factor during conjugation.
If gene X transferred at 99 minutes, what conclusion could you make about gene X?
Gene X is close to the fertility factor on the Hfr chromosome, but it is near the end of the chromosome transfer.
Which transduction is initiated during the lytic cycle of virulent bacteriophage?
Generalized transduction (the donor DNA can be ANY fragment of the bacterial chromosome which is why its called generalized)
How is generalized transduction different from specialized transduction?
Generalized transduction is initiated during lytic cycle of a virulent bacteriophage; specialized transduction is initiated during the lysogenic cycle of a temperate bacteriophage.
Transformation is a useful technique for making genetically modified bacteria in the laboratory. There have been efforts to transform Archaea, but it has been more difficult than transforming Bacteria. One reason that it has been difficult is that Archaea lack a peptidoglycan cell wall. Why does that affect the ability of researchers to develop techniques to transform them?
Genes for resistance to penicillin and related antibiotics can't be used as selectable markers.
How does an F+ cell differ from an Hfr cell?
Hfr strains have the F plasmid integrated into the chromosome.
__________ radiation such as X-rays and Gamma rays can cause some of the molecules within cells to lose electrons, becoming highly reactive ions and free radicals. Some of these reactive ions and free radicals can combine with bases on DNA resulting in errors in DNA replication and therefore mutations. Even more seriously these groups can react with the sugar phosphate backbone of DNA resulting in breaks in chromosomes.
Ionizing radiation. These rays are small enough to pass through your body
What benefit does the F- strain receive from mating with an Hfr strain?
It acquires new, potentially beneficial genes from the Hfr strain
Why would a recombinant DNA molecule be inserted into a host cell?
It can be copied, transcribed, and translated into a desired protein
What can specialized transduction can be used for? How does this happen?
It can be used to transfer antibiotic resistance from one bacterium to another. If the donor cell has a resistant gene R then as the prophage is excised or cut from the donor cell it will take the R gene with it and copy/pack this DNA (now containing the R gene) into phage particles that will transfer this DNA to another cell which incorporate the R gene into its own DNA.
What can result once the recombinant DNA molecule has been made?
It is inserted into a host cell, It is copied many times inside a host cell, and It can be transcribed and then translated into a desired protein.
what is unique about the DNA transferred between two cells during conjugation?
It is transferred as a single strand.
What is the function of the conjugation pilus?
It pulls the F+ and F- cells together.
_____________ radiation in the form of UV light is also mutagenic because it can cause adjacent Thymine bases to covalently bind to one another, producing Thymine dimers. Such dimers can cause serious harm or death to a cell if not repaired since these dimers prevent the cell from properly transcribing/replicating such DNA.
Nonionizing radiation. Can repaired if present in small amounts but not in large amounts.
If the codon is mutated to the sequence UAG, a stop codon, translation will stop prematurely, creating an incomplete protein that is likely to be faulty or nonfunctional. These are called ________ mutations.
Nonsense mutations. (stop codons are nicknamed nonsense codons)
How frequently do silent mutations occur?
One out of every three mutations
What happens to initiate specialized phage transduction?
Prophage integrates into the host genome AND bacteriophage enters lysogeny
How does replicative transposition differ from cut-and-paste transposition?
Replicative transposition results in multiple copies of the transposon in the DNA; cut-and-paste transposition has only one copy.
Which finding is most surprising from Griffith's experiments?
S strain cells are isolated from the blood of mice infected with heat-killed S strains and live R strains
What reason most likely explains the recovery of S strain from a mouse injected with heat-killed S strain mixed with living R strain?
The R strain picked up the S-strain DNA, enabling it to produce capsules.
What characteristic of the S strain allows it to evade the immune system of the mice?
The cells have a capsule.
During conjugation, if an Hfr cell is mated with an F- cell, why will the F- cell remain F-?
The cells would not stay in contact long enough for the entire Hfr genome to be transferred.
What happens to the packaged DNA of a specialized transduced phage when it infects a new recipient cell?
The host DNA integrates, with the prophage, into the new recipient chromosome.
How can a mismatch repair enzyme detect which strand contains the correct DNA sequence?
The original strand will likely have a methyl group attached, while the newly mutated strand will not.
Why is E. coli considered the model of bacterial conjugation?
The process of conjugation is best characterized in E. coli.
How does specialized transduction differ from regular lysogeny?
The prophage in specialized transduction carries with it pieces of the host chromosomal DNA.
How can specialized transduction contribute to the transfer of antibiotic resistance genes in a bacterial population?
The prophage takes an antibiotic resistance gene with it and is packaged with the newly synthesized viral DNA.
Why is a complex transposon containing an antibiotic resistance gene more likely to be copied than a simple insertion sequence when the host reproduces?
They confer a survival advantage for the host.
How do restriction enzymes cut DNA sequences?
They cut DNA at sites, called recognition sites, that have specific nucleotide sequences.
In a culture of bacteria, there are some individuals that are unable to synthesize histidine. What is the best and most likely description of how these individuals differ from the other bacteria in the culture?
They differ in their genotype and in their phenotype.
What is unique about complex transposons?
They have two simple transposons with another DNA sequence between them.
In general, how might recombinant DNA technology be used to prevent a genetic disorder caused by a mutation in a single gene?
To insert a desirable gene, remove an undesirable gene, or replace a defective gene with a functioning gene
What is unique about transduction compared to normal bacteriophage infection?
Transduction transfers DNA from the chromosome of one cell to another
DNA fragments that can move from one location in the DNA to another are called __________.
Transposons (can be simple or complex)
(mastery hw questions start) Frameshift mutations can be very severe. What is one reason why they are often so serious?
When a frameshift mutation occurs, it causes changes in many bases DOWNSTREAM (not upstream) and can affect many of the amino acids in the protein.
What DNA molecule is transferred between cells during conjugation between an F+ and an F- cell?
a single-stranded F plasmid
A "point mutation" refers to mutations involving
a substitution, deletion, or addition of one base-pair.
Insertion sequences are composed of _____________.
a transposase gene flanked by inverted repeats.
Which of the following methods may introduce foreign DNA into a recipient? transformation, transduction, conjugation or all of the above
all of the above
The fertility factor is also known as __________.
an F plasmid. (contained by F+ cells.
An organism that cannot synthesize methionine is called __________.
an auxotroph
A mutant that has a nutritional requirement for growth is an example of a(n)
auxotroph.
How does an F+ cell become an Hfr cell?
by integrating the F plasmid into the chromosome
when excision repair enzymes are used to repair thymine dimers, the enzymes are sometimes called __________ in contrast to light repair enzymes.
dark repair enzymes (excision repair can occur with or without light present)
The two major categories of mutagens are:
chemical mutagens and radiation mutagens
Cells that are naturally able to take up DNA from their environment are said to be ___________________.
competent
Which type of transposon would contain an antibiotic resistance gene?
complex transposons
A transducing phage
contains fragments of the host chromosome instead of the viral genome.
What is the function of the enzyme transposase? a.)It cuts the DNA so the transposon can leave its current position. b.) It cuts the DNA at the new site for a transposon. c.)It covalently links the transposon to the new DNA site. d.) All of the above answers apply.
d.) all of the above
What would be a fate of a bacterium infected by a generalized transducing bacteriophage?
integration of the packaged DNA into the host chromosome
A region of DNA in which the sequence of nucleotides is identical to an inverted sequence on the complementary strand is known as a(n) __________.
inverted repeat.
Enzymes known as photolyases are involved in which type of repair?
light repair
Cells have evolved repair enzymes to minimize the chance of mutation. These repair enzymes can be divided into three categories: ________, _________, and _________.
light repair enzymes, excision repair enzymes, and mis-match repair enzymes
Which repair mechanism(s) does not involve the removal of nucleotides?
light repair mechanisms
Which repair mechanisms might be involved in repairing a mutation that results from exposure to UV light?
light-repair mechanism AND excision-repair mechanism
__________ scan newly synthesized DNA for mismatches and when they find one, they change it.
mis-match repair enzymes
A chemical that can increase the rate of mutations is called a _______________________.
mutagen
While studying protein synthesis in the lab, you experimentally induce a mutation in a bacterium's DNA. You assess the proteins in the mutated bacterium and find that one of them is significantly shorter than its wild-type counterpart. Based on this information, what type of mutation did you induce?
nonsense mutation
5-bromouracil is a ___________ of thymine that often binds with guanine instead of adenine. This can lead to a base substitution mutation of a guanine for an adenine.
nucleoside analog
____________ are compounds that are structurally similar to normal nitrogenous bases but with different base pairing properties. These compounds can become incorporated into growing DNA during replication, replacing their related base. Once incorporated it can inhibit further replication or cause mismatching.
nucleoside analogs
The chemical mutagen that directly alters the structure of the nitrogenous bases of DNA are called _________.
nucleotide altering chemicals
The mutagens 2-aminopurine and 5-bromouracil are examples of
nucleotide base analogs.
Thymine dimers caused by UV light are the most common type of mutation. Some prokaryotes have evolved enzymes called _________ that use energy from visible light to break these thymine to thymine.
photolyase
The F (fertility) plasmid contains a set of genes that encode for the ________ proteins that are essential in conjugative transfer of DNA.
pili
Single base insertions or deletions cause _________.
reading frame errors. They are known as frameshift mutations
A plasmid may
replicate independently of the chromosome, integrate into the chromosome, or be transferred cell-to-cell during conjugation.
A mutation that affects the genotype of the organism but not the phenotype is called a
silent mutation
When a mutation results in the formation of the same amino acid as the wild type (the amino acid that would have formed if there was no mutation) then the final protein sequence will be the same. This mutation is considered a _________ mutation.
silent mutation
What mutation is the least likely to be harmful to a cell?
silent mutations
Base pair substitutions can result in what type(s) of mutation?
silent, missense, nonsense
Why must the recipient plasmid be cut with the same restriction enzyme?
to allow for a site in the plasmid for the donor DNA to attach. (it creates complementary sticky ends that allow the donor to attach)
What is the ultimate goal of recombinant DNA technology?
to improve the organism (by either adding desirable traits or removing undesirable traits)
What is the purpose of bacterial conjugation?
to transfer DNA between two living cells
Normally phage DNA is coated with phage protein to form new virus particles but sometimes pieces of bacterial DNA are mistakenly packaged in phage proteins. These sloppily packaged phage particles carry bacterial DNA rather than phage DNA and are called ___________.
transducing phages
The transfer of bacterial DNA from one host to another via a bacteriophage.
transduction
Increasing genetic variability by the uptake of DNA from the environment is __________.
transformation
The uptake of DNA released from a cell is ________, while transfer of DNA with cell-to-cell contact would most likely result in ________.
transformation / conjugation
Mutations that convert a purine to a purine ( A or G) or a pyrimidine to a pyrimidine (C or T) are called _______.
transitions
Transposons contain genes that code for ________ which is an enzyme that can cut the transposon out of one location in a chromosome and insert it in another.
transposase
After conjugation, each cell involved has a copy of the shared DNA. (true/false)
true
Almost all plasmids are double-stranded DNA.(true/false)
true
Intercalating agents, like acridine orange and ethidium bromide, lead to mutagenesis by pushing DNA base pairs apart, which can lead to insertions or deletions. (true/false)
true
