Lecture 9 / Chapters 6 and 10 - Bacteria and DNA Discovery Flashcards
In an interrupted mating experiment, the purpose of plating cells on a selective medium is _______.
- to ensure that only recombinant genotypes are recovered
- to determine the genes present in the Hfr
- to eliminate all recipient cells
- to ensure that conjugation has been completed
To ensure that only recombinant genotypes are recovered.
(Selective media in these experiments allow the elimination of parental genotypes and recovery of only those whose genotypes result from the transfer of donor genes.)
Mapping bacterial genes by conjugation is based on which of the following assumptions?
- F minus bacterial strains are capable of transferring genes to Hfr strains
- Genes are transferred from donor to recipient in a linear fashion
- Bacterial cells are capable of growing in the presence of sodium azide
- Conjugation is not disrupted when a bacterial culture is mixed in a blender
Genes are transferred from donor to recipient in a linear fashion.
(If this were not true, the distance between genes could not be measured as a function of time.)
Which of the following statements about mapping bacterial genes by conjugation is NOT true?
- Two genes that are very close together may appear to be transferred at the same time
- The closer a gene to the Hfr origin, the more likely it will be transferred to the recipient during conjugation
- For any two genes transferred from donor to recipient, all genes residing between them have also been transferred
- It is necessary that all Hfr cells be absent from the population of cells recovered for genotyping
The closer a gene to the Hfr origin, the more likely it will be transferred to the recipient during conjugation.
(This is false - it depends on which side of the origin the gene resides.)
What is a form of recombination in bacteria that involves the F plasmid?
Conjugation.
True or false?
A bacterial strain that is pro + thi + leu − met − will grow on minimal media plus leucine and thiamine.
False.
(The strain is auxotrophic for leucine and methionine, meaning that it cannot synthesize those nutrients. Thus, it requires those two nutrients to be added to minimal media for growth.)
Which of the following statements about conjugation is true?
- One strand of DNA from an F+ cell integrates into the chromosome of an F- cell, and the other strand is degraded
- DNA is transferred from an F+ cell to an F- cell
- Only competent cells can undergo conjugation
- The F factor is an element that is found in the chromosome of an F+ cell
DNA is transferred from an F+ cell to an F- cell.
DNA is transferred through a pilus from an F+ cell to an F- cell.
How is a merozygote formed?
- The F factor is excised from the chromosome of an Hfr strain, causing it to revert to F-
- The F factor and several adjacent genes are excised from the chromosome of an F+ cell and transferred to an F- strain
- The F factor is inserted into the chromosome of an F+ cell, causing it to revert to F-
- The F factor is inserted into the chromosome of an F- cell, causing it to become an Hfr strain
The F factor and several adjacent genes are excised from the chromosome of an F+ cell and transferred to an F- strain.
(A merozygote is formed when the F factor and several adjacent bacterial genes are excised from the bacterial chromosome of an F+ cell and transferred to an F- cell.)
Strain 1: arg+ thi- pro- val+
Strain 2: arg- thi+ pro+ val-
Producing Strain 3: arg+ thi- pro- val+ and arg- thi+ pro+ val-
Use the figure to predict the results of Lederberg and Tatum’s experiment.
Bacterial cultures from which flask(s) will grow on minimal medium plus pro?
Flask 3.
(Minimal medium only supports the growth of bacteria that are wild type for all growth requirements. When minimal medium is supplemented with proline, it can support the growth of pro - bacteria, but these bacteria must be wild type for other genes. Because strains 1 and 2 have additional mutations, and are auxotrophs, they will not grow under this condition. However, genetic exchange can occur between these two auxotrophic strains when combined together in flask 3, which can produce prototrophs that are wild type for all growth requirements and capable of growing in this condition.)
Strain 1: arg+ thi- pro- val+
Strain 2: arg- thi+ pro+ val-
Producing Strain 3: arg+ thi- pro- val+ and arg- thi+ pro+ val-
Use the figure to predict the results of Lederberg and Tatum’s experiment.
Bacterial cultures from which flask(s) will grow on complete medium?
Flasks 1, 2, and 3
Complete medium is extensively supplemented and can support the growth of auxotrophs and phototrophs.
Strain 1: arg+ thi- pro- val+
Strain 2: arg- thi+ pro+ val-
Producing Strain 3: arg+ thi- pro- val+ and arg- thi+ pro+ val-
Use the figure to predict the results of Lederberg and Tatum’s experiment.
Bacterial cultures from which flask(s) will grow on minimal medium plus val?
Flask 3.
(Minimal medium only supports the growth of bacteria that are wild type for all growth requirements. When minimal medium is supplemented with valine, it can support the growth of val - bacteria, but these bacteria must be wild type for other genes. Because strains 1 and 2 have additional mutations, and are auxotrophs, they will not grow under this condition. Genetic exchange can occur between these strains when combined together in flask 3, which can produce prototrophs which are wild type for all growth requirements and capable of growing in this condition.)
Strain 1: arg+ thi- pro- val+
Strain 2: arg- thi+ pro+ val-
Producing Strain 3: arg+ thi- pro- val+ and arg- thi+ pro+ val-
Use the figure to predict the results of Lederberg and Tatum’s experiment.
Bacterial cultures from which flask(s) will grow on minimal medium plus pro and thi?
Flasks 1 and 3.
(Minimal medium can only support the growth of bacteria that are wild type for all growth requirements, and if supplemented with proline and thiamine, can support growth of bacteria that are pro - and thi -, if they are wild type for other genes.)
Strain 1: arg+ thi- pro- val+
Strain 2: arg- thi+ pro+ val-
Producing Strain 3: arg+ thi- pro- val+ and arg- thi+ pro+ val-
Use the figure to predict the results of Lederberg and Tatum’s experiment.
Bacterial cultures from which flask(s) will grow on minimal medium plus val and arg?
Flasks 2 and 3.
(Minimal medium can only support the growth of bacteria that are wild type for all growth requirements. If valine and arginine are added to this medium, it can support growth of bacteria that are val - and arg -, if they are wild type for other genes.)
Strain 1: arg+ thi- pro- val+
Strain 2: arg- thi+ pro+ val-
Producing Strain 3: arg+ thi- pro- val+ and arg- thi+ pro+ val-
Use the figure to predict the results of Lederberg and Tatum’s experiment.
Bacterial cultures from which flask(s) will grow on minimal medium?
Flask 3.
(The bacteria in strains 1 and 2 are auxotrophs and cannot grow in minimal medium. However, because genetic exchange can occur between these strains when combined together in flask 3, prototrophs which are wild type for all growth requirements can be produced. They are capable of growing in this simple medium.)
Name the general category into which double-stranded circular extrachromosomal DNA elements such as F factors, ColE1, and R would fall.
- r-determinant
- partial diploid
- plasmid
- plaque
- capsid
Plasmid.
True or False?
An Hfr cell can initiate chromosome transfer from one E. coli to another.
True.
With respect to F+ and F- bacterial matings, how was it established that physical contact was necessary?
- By placing a filter in a U-tube between bacterial cells. Under this condition, conjugation does not occur.
- By placing bacterial cells in a U-tube. Under this condition, conjugation does not occur.
- By placing a filter in a U-tube between bacterial cells. Under this condition, conjugation occurs.
- By placing bacterial cells in a U-tube. Under this condition, conjugation occurs.
By placing a filter in a U-tube between bacterial cells. Under this condition, conjugation does not occur.
By treating cells with streptomycin, an ______, it was shown that recombination _______ if one of the two bacterial strains was ______. However, if the other was similarly treated, recombination _______. Thus, directionality was suggested, with one strain being a donor strain and the other being the _______.
Options:
- activator
- antibiotic
- recipient
- inactivator
- would occur
- would not occur
- inactivated
- activated
- antibiotic
- would not occur
- inactivated
- would occur
- recipient
What is the genetic basis of a bacterium being F+?
- it lacks the F- plasmid
- it lacks the F- sequence in its genome
- it contains the F+ plasmid
- it contains the F+ sequence in its genome
It contains the F+ plasmid.
Describe the origin of F+ bacteria and merozygotes.
The _____ element can enter the host bacterial chromosome, and upon returning to its independent state, it may _____ a piece of a bacterial chromosome. When transferred to a bacterium with a _______, a ______ or merozygote is formed.
Options:
- pick up
- partial diploid
- F+
- F-
- reduced chromosome
- complete chromosome
- leave
- Hfr
- F+
- pick up
- complete chromosome
- partial diploid
How do we know that bacteria undergo genetic recombination, allowing the transfer of genes from one organism to another?
- From experiments involving conjugation
- From experiments involving transduction
- From experiments involving transformation
- From a variety of experiments involving transformation, conjugation, and transduction
From a variety of experiments involving transformation, conjugation, and transduction.
How do we know that conjugation leading to genetic recombination between bacteria involves cell contact, which precedes the transfer of genes from one bacterium to another?
- involving a Davis U-tube and a filter: when the filter separated two auxotrophic strains, genetic recombination occurred
- involving a Davis U-tube and a filter: when the filter separated two auxotrophic strains, NO genetic recombination occurred
- involving a Davis U-tube: when the tube separated two auxotrophic strains, NO genetic recombination occurred
- involving a Davis U-tube: when the tube separated two auxotrophic strains, genetic recombination occurred
Involving a Davis U-tube and a filter: when the filter separated two auxotrophic strains, NO genetic recombination occurred.
How do we know that during transduction bacterial cell-to-cell contact is not essential?
- Bacterial contact can be eliminated with a U-tube
- Bacterial contact can be eliminated with a filter
- This is a hypothesis
Bacterial contact can be eliminated with a filter.
How do we know that intergenic exchange occurs in bacteriophages?
- It was demonstrated by using a Davis U-tube without a filter
- It was demonstrated by using a Davis U-tube and a filter
- It was demonstrated by mixed infections that yielded recombinants
- It was demonstrated by a single infection that yielded recombinants
It was demonstrated by using a Davis U-tube and a filter.
Why are the recombinants produced from an Hfr × F−
cross rarely, if ever, F+?
- Because the F factor is the last element to be transferred and the conjugation tube is fragile, the liklihood for complete transfer is low
- Because the F factor is the last element to be transferred, the likelihood for complete transfer is low
- Because the conjugation tube is fragile, the likelihood for complete transfer is low
- Because the F factor is the first element to be transferred, the likelihood for complete transfer is high
Because the F factor is the last element to be transferred and the conjugation tube is fragile, the liklihood for complete transfer is low.
All EXCEPT which of the following are characteristics of the genetic material?
- It is composed of protein
- It must be replicated accurately
- It contains all the information needed for growth, development, and the reproduction of the organism
- It must be capable of change
It is composed of protein.
(Although early observations favored protein as the genetic material, subsequent experiments demonstrated that the genetic material was nucleic acid.)
In 1928, Frederick Griffith established that _______.
- mouse DNA could be transferred into bacterial cells
- proteases have no effect on DNA
- heat-killed bacteria harbor the constituents necessary to convey genetic properties to living bacteria
- mice could be infected with bacteria
Heat-killed bacteria harbor the constituents necessary to convey genetic properties to living bacteria.
(Because some of the nonvirulent bacteria acquired properties of the virulent bacteria, instructions for this transformation must be carried by the virulent bacteria.)
To be certain that the extract prepared from virulent cells still contained the transforming principle that was present prior to lysis, Avery _______.
- injected mice with the extract
- incubated virulent cells with complete extract
- destroyed proteins, polysaccharides, DNA, and RNA contained in the extract
- incubated nonvirulent cells with the complete extract
Incubated nonvirulent cells with the complete extract.
(The complete extract possessed the same ability to induce transformation in IIR bacteria as whole heat-killed IIS bacteria.)
If Avery had observed transformation using only the extracts containing degraded DNA, degraded RNA, and degraded protein, but NOT the extract containing degraded polysaccharides, he would have concluded that _______.
- polysaccharides are the genetic material
- RNA is the genetic material
- the preparations were contaminated
- mice with diets rich in polysaccharides are resistant to bacterial infection
Polysaccharides are the genetic material.
(Failure to transform suggests that the chemical degraded in that preparation is the one responsible for transformation, in this case polysaccharides.)
The Hershey and Chase experiments involved the preparation of two different types of radioactively labeled phage. Which of the following best explains why two preparations were required?
- Each scientist had his own method for labeling phages, so each conducted the same experiment using a different isotope.
- The bacteriophage used in the experiments was a T2 phage.
- Establishing the identity of the genetic material required observation of two phage generations.
- It was necessary that each of the two phage components, DNA and protein, be identifiable upon recovery at the end of the experiment.
It was necessary that each of the two phage components, DNA and protein, be identifiable upon recovery at the end of the experiment.
(Because it was concluded that the component associated with bacteria at the end of the experiment must be the genetic material, it was critical that the component be identifiable as either DNA or protein.)
Which of the following statements best represents the central conclusion of the Hershey-Chase experiments?
- Phage T2 is capable of replicating within a bacterial host
- Some viruses can infect bacteria
- When radioactive sulfur is supplied in a growth medium, it is primarily DNA that incorporates radioactive label
- DNA is the identity of the hereditary material in phage T2
DNA is the identity of the hereditary material in phage T2.
(Because phage DNA and not protein were associated with bacteria at the end of the experiment, it could be concluded that DNA - not protein - must be the genetic material.)
