C9 Brock Sample Questions

Question 1

A mutant that has a nutritional requirement for growth is an example of a(n)
A) autotroph.
B) auxotroph.
C) heterotroph.
D) organotroph.

Answer 1

B) auxotroph.

An auxotroph is a mutant that requires a specific nutrient for growth, which was not required by the wild-type organism.

Question 2

Consider a mutation in which the change is from UAC to UAU. Both codons specify the amino acid tyrosine. Which type of point mutation is this?
A) silent mutation
B) nonsense mutation
C) missense mutation
D) frameshift mutation

Answer 2

A) silent mutation

Since both UAC and UAU codons code for tyrosine, the mutation does not change the amino acid sequence, making it a silent mutation.

Question 3

A mutation that readily reverses to restore the original parental type would most likely be due to a(n)
A) deletion.
B) insertion.
C) point mutation.
D) frameshift mutation.

Answer 3

C) point mutation.

Point mutations are more likely to be reversed compared to larger-scale mutations like deletions or insertions, which can have more profound effects on the genome.

Question 4

Which process listed below allows genetic material to be transferred from a virus-like particle that lacks genes for its own replication?
A) conjugation of an F+ plasmid
B) gene transfer through a gene transfer agent
C) transduction by a dsDNA phage Mu
D) transformation of a linear piece of DNA

Answer 4

C) transduction by a dsDNA phage Mu

Transduction involves the transfer of DNA from one bacterium to another through a viral vector (bacteriophage), which can lack genes for its own replication.

Question 5

The mutagens 2-aminopurine and 5-bromouracil are examples of
A) alkylating agents.
B) nucleotide base analogs.
C) chemicals reacting with DNA.
D) None of the answers are correct.

Answer 5

B) nucleotide base analogs.

Both 2-aminopurine and 5-bromouracil are structural analogs of nucleotide bases, which can incorporate into DNA and cause mutations.

Question 6

The killing of cells by UV irradiation involves
A) absorption at 260 nm by proteins only.
B) absorption at 260 nm by RNA only.
C) formation of pyrimidine dimers.
D) formation of purine dimers.

Answer 6

C) formation of pyrimidine dimers.

UV radiation is known to cause the formation of pyrimidine dimers in DNA, leading to DNA damage and potentially cell death.

Question 7

Ionizing radiation does NOT include
A) gamma rays.
B) UV rays.
C) X-rays.
D) cosmic rays.

Answer 7

B) UV rays.

Ionizing radiation has enough energy to remove tightly bound electrons from atoms, typically including X-rays, gamma rays, and cosmic rays, but not UV rays, which are non-ionizing.

Question 8

Which of the following methods may introduce foreign DNA into a recipient?
A) transformation
B) transduction
C) conjugation
D) transformation, transduction, and conjugation

Answer 8

D) transformation, transduction, and conjugation

All three processes can introduce foreign DNA into a recipient cell: transformation (free DNA uptake), transduction (via a bacteriophage), and conjugation (direct cell-to-cell transfer).

Question 9

The uptake of free DNA from the environment ______, while transfer of DNA with cell-to-cell contact would most likely result in _______.
A) transformation / conjugation
B) transduction / conjugation
C) conjugation / transformation
D) transformation / transduction

Answer 9

A) transformation / conjugation

Uptake of free DNA is the definition of transformation, while cell-to-cell contact typically involves conjugation.

Question 10

Which of the following is NOT required for homologous recombination?
A) an Hfr chromosome
B) RecA
C) proteins having helicase activity
D) endonuclease

Answer 10

A) an Hfr chromosome

Homologous recombination can occur without an Hfr (High Frequency of Recombination) chromosome, which is specifically involved in conjugational transfer of chromosomal DNA.

Question 11

Consider the following experiment. First, large populations of two mutant strains of Escherichia coli are mixed, each requiring a different, single amino acid. After plating them onto a minimal medium, 45 colonies grew. Which of the following may explain this result?
A) The colonies may be due to back mutation (reversion).
B) The colonies may be due to recombination.
C) Either A or B is possible.
D) Neither A nor B is possible.

Answer 11

C) Either A or B is possible.

The growth of colonies on minimal medium could be due to either back mutation (reversion) of one of the mutants or recombination between the two mutants, restoring the ability to grow.

Question 12

You have performed the following mating experiment using Hfr and F-strains of Escherichia coli:
Hfr (thr+ leu+ gal+ strs) × F- (thr- leu- gal- strr). Which of the following selective media would you use to score recombinant colonies?
A) minimal medium
B) minimal medium + streptomycin
C) minimal medium + threonine
D) minimal medium + streptomycin + threonine

Answer 12

D) minimal medium + streptomycin + threonine

To select for recombinants that have received the thr+ gene (allowing growth on minimal medium without threonine) and are resistant to streptomycin (strr), both streptomycin and threonine should be included.

Question 13

Horizontal gene transfer in Archaea
A) is infrequent in nature and therefore difficult to use for genetic studies in the laboratory.
B) has not been documented, thus all genetic studies of archaea are done via genomic sequencing.
C) frequently occurs in nature and has been used to perform genetic studies in the laboratory as well.
D) frequently occurs in nature, but there are very few laboratory studies because archaea do not cause human disease.

Answer 13

C) frequently occurs in nature and has been used to perform genetic studies in the laboratory as well.

While less studied than in Bacteria, horizontal gene transfer is known to occur in Archaea and has been utilized in genetic studies.

Question 14

The minimal amount of genetic information required for specialized transduction would include A) the att
B) the cos
C) a helper phage.
D) the att region, cos site, and a helper phage.

Answer 14

A) the att

The attachment site (att) is crucial for the integration and excision of bacteriophages, which is necessary for specialized transduction.

Question 15

Lysogeny probably carries a strong selective advantage for the host cell because it
A) prevents cell lysis.
B) confers resistance to infection by viruses of the same type.
C) confers resistance to infection by viruses of a different type (or strain).
D) confers resistance to infection by many virus types and prevent cell lysis.

Answer 15

B) confers resistance to infection by viruses of the same type.

Lysogeny, where a bacteriophage genome integrates into the host’s chromosome, often confers immunity to superinfection by the same or closely related phages.

Question 16

A plasmid may
A) replicate independently of the chromosome.
B) be transferred cell-to-cell during conjugation.
C) be integrated into the chromosome.
D) replicate independently of the chromosome, integrate into the chromosome, or be transferred cell-to-cell during conjugation.

Answer 16

D) replicate independently of the chromosome, integrate into the chromosome, or be transferred cell-to-cell during conjugation.

Plasmids are known for their ability to replicate autonomously, integrate into the host chromosome (in some cases), and be transferred between cells via conjugation.

Question 17

Plasmids that govern their own transfer are known as A) transformable.
B) transmutable.
C) conjugative.
D) transfective.

Answer 17

C) conjugative.

Conjugative plasmids encode the necessary genes for their own transfer from one bacterium to another through direct cell-to-cell contact.

Question 18

Homologous recombination has been observed in
A) Archaea.
B) Bacteria.
C) Eukarya.
D) All three domains (Archaea, Bacteria, and Eukarya).

Answer 18

D) All three domains (Archaea, Bacteria, and Eukarya).

Homologous recombination is a universal mechanism for DNA repair and recombination found across all domains of life.

Question 19

Hfr strains of Escherichia coli
A) do not possess an F factor.
B) have the F factor as a plasmid.
C) have an integrated F factor.
D) transfer the complete F factor to recipient cells at a high frequency.

Answer 19

C) have an integrated F factor.

High Frequency of Recombination (Hfr) strains have the F (fertility) plasmid integrated into their chromosome, enabling high-frequency transfer of chromosomal genes.

Question 20

F+ strains of Escherichia coli
A) do not have an F factor.
B) have the F factor as a plasmid.
C) have an integrated F factor.
D) transfer the F factor to recipient cells at a high frequency.

Answer 20

B) have the F factor as a plasmid.

F+ (F plus) strains carry the F factor as a free, autonomous plasmid, not integrated into the chromosome.

Question 21

F- strains of Escherichia coli
A) do not have an F factor.
B) have the F factor as a plasmid.
C) have an integrated F factor.
D) transfer the F factor to other strains at a high frequency.

Answer 21

A) do not have an F factor.

F- (F minus) strains lack the F factor, which is necessary for initiating conjugation.

Question 22

All Hfr strains integrate into the chromosome at
A) the same locus.
B) several specific sites.
C) the same locus most of the time, although there may be some variation.
D) loci that cannot be accurately determined.

Answer 22

B) several specific sites.

While there can be some variation, Hfr strains typically integrate the F factor into one of several preferred or “hot” integration sites within the chromosome.

Question 23

Transposition is a(n)
A) homologous recombination event.
B) analogous recombination event.
C) site-specific recombination event.
D) general recombination event.

Answer 23

C) site-specific recombination event.

Transposition involves the movement of a transposon from one location to another within a genome, often through site-specific recombination mechanisms.

Question 24

The enzyme transposase may be coded for by insertion sequences on a A) chromosome.
B) phage.
C) plasmid.
D) chromosome, phage, or plasmid.

Answer 24

D) chromosome, phage, or plasmid.

Transposase, the enzyme facilitating transposition, can be encoded by genes located on various genetic elements, including chromosomes, phages, or plasmids.

Question 25

A ʺpoint mutationʺrefers to mutations involving
A) a base-pair substitution.
B) the gain of a base pair (microinsertion).
C) the deletion of a base pair (microdeletion).
D) a substitution, deletion, or addition of one base-pair.

Answer 25

D) a substitution, deletion, or addition of one base-pair.

Point mutations are defined by small, localized changes in the DNA sequence, encompassing substitutions, deletions, or insertions of a single base pair.

Question 26

A deleterious mutation in recA results in
A) a decrease in specific recombination.
B) a decrease in homologous recombination.
C) an increase in homologous recombination.
D) no change in either general or specific recombination.

Answer 26

B) a decrease in homologous recombination.

The RecA protein is crucial for homologous recombination in bacteria; a deleterious mutation in recA would impair this process.

Question 27

The production of a functional gene product by transforming bacteria that lack a lacZ gene with a plasmid containing a lacZ gene is known as
A) complementation.
B) mitosis.
C) transfection.
D) reversion.

Answer 27

A) complementation.

Providing a functional gene to a mutant bacterium that lacks it, resulting in the production of a functional gene product, is an example of genetic complementation.

Question 28

Consider conjugation in Escherichia coli. In which of the following matings would chromosomal genes be transferred most frequently?
A) F+ × F-
B) F- × F-
C) Hfr × F-
D) F+ x F+

Answer 28

C) Hfr × F-

Hfr (High Frequency of Recombination) strains are designed for the high-frequency transfer of chromosomal genes to F- (recipient) strains.

Question 29

Which of the following features are common to transformation, transduction, and conjugation?
(1) unidirectional transfer of genes
(2) incomplete gene transfer
(3) homologous recombination
(4) meiosis occurring in the recipient
A) 1, 2, 3
B) 1, 2
C) 3, 4
D) 1, 2, 4

Answer 29

B) 1, 2

All three processes involve the unidirectional transfer of genes (1) and can result in incomplete gene transfer (2). Homologous recombination (3) is not a defining feature of all three, and meiosis (4) is not relevant to prokaryotic gene transfer.

Question 30

Which of the following is most similar to lysogeny?
A) Hfr state
B) F+ state
C) F- state
D) Fʹ state

Answer 30

D) Fʹ state

Similar to lysogeny (where a phage integrates into the host chromosome), an Fʹ (F prime) state involves a plasmid (derived from the F plasmid) integrating into the bacterial chromosome, carrying some host genes with it.

Question 31

In the bacterial world, a gene located on which of the following would be the LEAST likely to be transferred?
A) a resistance plasmid
B) An F plasmid
C) the phage Mu
D) the chromosome

Answer 31

D) the chromosome

While chromosomal genes can be transferred (e.g., via Hfr conjugation), genes located on the chromosome are generally less mobile compared to those on plasmids, phages, or other mobile genetic elements.

Question 32

Genetic recombination involving insertion sequences typically results in what type of mutation? A) base-pair substitution mutation
B) silent mutation
C) frameshift mutation
D) base-pair deletion mutation

Answer 32

C) frameshift mutation

Insertion sequences (IS) can cause frameshift mutations when they insert into a new location within a gene, altering the reading frame of the genetic code.

Question 33

The SOS regulatory system is activated by
A) the activity of DNA polymerase IV.
B) DNA damage.
C) Transcription of LexA.
D) repression of RecA.

Answer 33

B) DNA damage.

The SOS response is a DNA repair mechanism activated in response to DNA damage, which can be caused by various factors including UV light, chemical mutagens, and replication errors.

Question 34

Which of the following factors has delayed the development of laboratory-based genetic systems in Archaea?
A) There are no documented systems of conjugation in Archaea.
B) Homologous recombination does NOT occur in Archaea.
C) Archaea do NOT host viruses or plasmids.
D) Many archaea grow in extreme or unusual conditions that make the use of agar and traditional mutant screening techniques problematic.

Answer 34

D) Many archaea grow in extreme or unusual conditions that make the use of agar and traditional mutant screening techniques problematic.

The unique, often extreme, growth requirements of many archaeal species pose significant technical challenges for developing genetic systems comparable to those in Bacteria or Eukarya.

Question 35

Transformation and homologous recombination allow for the formation of heteroduplex DNA. Which of the following would occur during DNA replication of this molecule?
A) One daughter strand is complementary to the recombinant DNA molecule, while the other daughter strand is complementary to the parent DNA molecule.
B) Both daughter strands are complementary to the recombinant DNA molecule.
C) Both daughter strands are complementary to the parent DNA molecule.
D) None of the answers are correct.

Answer 35

B) Both daughter strands are complementary to the recombinant DNA molecule.

Upon replication, the heteroduplex DNA (containing one strand from each parent) will separate, and each strand will serve as a template for a new, fully complementary strand, resulting in two recombinant DNA molecules.

Question 36

You work for a biotechnology company that uses Streptomyces strains to produce pharmaceutical products. A phage has infected and killed some of your Streptomyces strains during production, resulting in dramatically decreased yields. To protect the strains from infection you propose to
A) introduce gene transfer agents into the Streptomyces cultures to transfer antibiotic resistance genes into your Streptomyces
B) design and insert CRISPR spacer sequences into the genomes of your strains that are complementary to the genomes of the phages that are infecting the cultures.
C) infect the Streptomyces strains with a helper phage that will help the strains resist infection.
D) transform the Streptomyces strains with plasmids encoding antibody proteins that will protect them from phage infection.

Answer 36

B) design and insert CRISPR spacer sequences into the genomes of your strains that are complementary to the genomes of the phages that are infecting the cultures.

This approach utilizes the CRISPR-Cas system for targeted defense against specific phages, providing a precise and effective method for protecting the strains.

Question 37

Hfr means high frequency of _________, and these cells are capable of transferring genes from their _________ to other cells.
A) transformation / chromosome
B) transduction / plasmids
C) recombination / chromosome
D) transduction / chromosome

Answer 37

C) recombination / chromosome

Hfr (High Frequency of Recombination) cells have the F plasmid integrated into their chromosome, enabling the high-frequency transfer of chromosomal genes to recipient cells.

Question 38

Mutation rates are similar in Bacteria and Archaea, yet certain stressful conditions mutation rates increase. Why is the mutation rate not constant and close to zero all of the time?
A) Increased mutation rates can be advantageous in rapidly changing environments because some random mutations may be useful for survival.
B) Microorganisms carefully control the mutation rate of their DNA to match the environmental conditions and maximize evolution.
C) The increased mutation rate under stressful conditions is an indication that the microorganisms can no longer replicate their DNA properly and are about to die.
D) Constant mutation rates would halt evolution completely.

Answer 38

A) Increased mutation rates can be advantageous in rapidly changing environments because some random mutations may be useful for survival.

Elevated mutation rates under stress can provide a selective advantage by increasing genetic diversity, thus enhancing the likelihood of mutations that confer survival benefits in changing environments.

Question 39

Chemical mutagens, UV radiation, and ionizing radiation all increase mutation rates, but they have different mechanisms. Which type of mutagen would be best suited for creating large deletions and rearrangements within a genome?
A) chemical mutagens
B) UV radiation
C) ionizing radiation
D) Chemical, UV, and ionizing radiation would create large deletions and rearrangements if used in a very high dose.

Answer 39

C) ionizing radiation

Ionizing radiation has sufficient energy to cause double-strand breaks and other severe DNA damage, leading to large deletions and chromosomal rearrangements.

Question 40

) The SOS system repairs DNA that has gaps, breaks, and other lesions by
A) cutting DNA from other parts of the genome and pasting it into the gaps or damaged areas.
B) stabilizing single-stranded DNA until the next round of normal replication.
C) using specialized DNA polymerases that will synthesize a new DNA strand even if there is not a normal complementary DNA strand to act as a template.
D) using available mRNA and a special RNA-dependent DNA polymerase to fill in the gaps and replace damaged DNA.

Answer 40

C) using specialized DNA polymerases that will synthesize a new DNA strand even if there is not a normal complementary DNA strand to act as a template.

The SOS response includes error-prone DNA polymerases (e.g., Pol IV and Pol V in E. coli) that can bypass or repair DNA lesions, although sometimes introducing mutations.

Question 41

Microinsertions and microdeletions often result in ______ mutations.
A) auxotrophic
B) advantageous
C) silent
D) frameshift

Answer 41

D) frameshift

The insertion or deletion of one or a few nucleotides can shift the reading frame of the genetic code, leading to frameshift mutations.

Question 42

When damaged or single-stranded DNA activates the RecA protein, the RecA protein stimulates the cleavage of LexA. This results in
A) repression of polymerase V and activation of endonuclease.
B) activation of the Hfr system.
C) derepression of the SOS system.
D) increased transduction and recombination.

Answer 42

C) derepression of the SOS system.

Activation of RecA leads to the cleavage of LexA, a repressor protein, thereby derepressing the SOS regulon and initiating DNA repair and other SOS response functions.

Question 43

The F (fertility) plasmid contains a set of genes that encode for the proteins that are essential in conjugative transfer of DNA.
A) pili
B) SOS repair
C) transduction
D) transformation

Answer 43

A) pili

The F plasmid encodes genes necessary for the formation of sex pili, which are crucial for the initiation of conjugation and the transfer of DNA between bacterial cells.

Question 44

The designations Phe-, Leu-, and Ser+ refer to an organismʹs
A) plasmid type.
B) genotype.
C) phenotype.
D) mutation type.

Answer 44

C) phenotype.

These designations indicate the organism’s phenotypic traits regarding the metabolism or requirement for specific amino acids (Phe, Leu, Ser), reflecting its observable characteristics.

Question 45

If a bacterium carrying a plasmid that confers resistance to ampicillin is placed into medium without ampicillin, it may A) gain resistance to other antibiotics.
B) transfer resistance to other cultures in the laboratory.
C) undergo a reversion mutation.
D) lose the plasmid because there is no selection for ampicillin resistance.

Answer 45

D) lose the plasmid because there is no selection for ampicillin resistance.

Without the selective pressure of ampicillin, there is no advantage to maintaining the resistance plasmid, and the bacterium may lose it over time due to the metabolic cost of plasmid maintenance.

Question 46

When DNA is transferred into a prokaryotic cell it may
A) be degraded by enzymes.
B) replicate independent of the host chromosome.
C) recombine with the host chromosome.
D) be degraded by enzymes, replicate independent of the host chromosome, or recombine with the host chromosome.

Answer 46

D) be degraded by enzymes, replicate independent of the host chromosome, or recombine with the host chromosome.

Incoming DNA in prokaryotes can indeed be degraded by restriction enzymes, replicate autonomously if it’s a plasmid, or integrate into the host chromosome through recombination.

Question 47

The process in which related DNA sequences from two different sources are exchanged is called
A) transduction.
B) phage conversion.
C) reversion.
D) homologous recombination.

Answer 47

D) homologous recombination.

Homologous recombination involves the exchange of genetic material between two DNA strands of similar sequence, a fundamental process in genetics.

Question 48

Integration of linear transforming DNA into the chromosome
A) is not required for the expression for the transformed genes.
B) is catalyzed by the RecA gene.
C) almost never occurs because restriction endonuclease will degrade the DNA before it is integrated.
D) only occurs in laboratory-based systems in artificial competent cells.

Answer 48

B) is catalyzed by the RecA gene.

While RecA is crucial for homologous recombination, the integration of linear transforming DNA into the chromosome typically involves other enzymes and processes, but RecA plays a role in the broader context of recombination.

Question 49

High-efficiency, natural transformation
A) is common in Bacteria and
B) requires specialized DNA uptake, DNA binding, and integration proteins.
C) is only common in Archaea.
D) usually involves plasmids.

Answer 49

B) requires specialized DNA uptake, DNA binding, and integration proteins.

Naturally transformable bacteria have evolved specific mechanisms, including proteins for DNA uptake, binding, and integration, to facilitate the efficient acquisition of free DNA.

Question 50

The CRISPR system
A) facilitates homologous recombination through a complex system of proteins and clustered repeats.
B) recognizes foreign DNA sequences that have previously entered the cell and directs the Cas proteins to destroy them.
C) repairs DNA and increases DNA damage tolerance during times of stress.
D) synthesizes gene transfer agents during stationary phase.

Answer 50

B) recognizes foreign DNA sequences that have previously entered the cell and directs the Cas proteins to destroy them.

The CRISPR-Cas system is a prokaryotic immune mechanism that identifies and degrades foreign DNA, such as from phages or plasmids, that match the sequences stored in the CRISPR array.

Question 51

Which of the following is the correct abbreviation for a mutation in a gene that synthesizes one of the enzymes involved in tryptophan production?
A) TrpC
B) trp
C) Trp-
D) trpC1

Answer 51

D) trpC1

In bacterial genetics, “trp” denotes genes involved in tryptophan biosynthesis, with the letter (e.g., “C”) indicating a specific gene within the pathway, and the number (e.g., “1”) specifying the particular mutation.

Question 52

Which of the following is TRUE of competence?
A) It is not required for transformation.
B) It commonly occurs with high efficiency in nature.
C) It cannot occur naturally in bacteria.
D) It requires special proteins such as a cell wall autolysin.

Answer 52

D) It requires special proteins such as a cell wall autolysin.

Competence for transformation involves a series of specialized proteins, including autolysins that modify the cell wall to allow DNA uptake.

Question 53

What is one of the changes that occur when a cell contains an F plasmid that is NOT integrated into the chromosome?
A) It is no longer able to produce a pilus.
B) Cell surface receptors change, preventing the uptake of more plasmids through conjugation.
C) Mutation rates are decreased.
D) The cell is considered an Hfr cell.

Answer 53

D) The cell is considered an Hfr cell.

This statement is incorrect regarding the provided options as the correct answer; an F+ cell (carrying a non-integrated F plasmid) is not considered an Hfr cell. However, given the options, the best fitting answer based on the question’s intent might be misinterpreted. The correct distinction should highlight that an F+ cell can initiate conjugation but does not necessarily integrate the plasmid into its chromosome like an Hfr cell would. A more accurate question would contrast F+ with

Question 54

UV radiation is a useful tool in producing mutants of microbial cultures.

Answer 54

TRUE: UV radiation can induce mutations in microbial cultures by causing DNA damage, which can lead to genetic variations upon repair.

Question 55

When UV radiation damage occurs, DNA repair occurs only in the absence of template instruction.

Answer 55

FALSE: Some DNA repair mechanisms, like template-dependent repair (e.g., nucleotide excision repair), require a template for accurate repair.

Question 56

Following uptake, transforming DNA becomes attached to a competence-specific protein that prevents it from nuclease attack until it reaches the chromosome.

Answer 56

TRUE: In competent bacterial cells, taken-up DNA is indeed protected from nucleases by binding to specific proteins, ensuring its integrity until integration.

Question 57

The evolutionary significance of phage conversion likely stems from an effective alteration of host cells.

Answer 57

TRUE: Phage conversion (lysogenic conversion) can significantly alter the host bacterium’s phenotype, often contributing to virulence or other evolutionary advantages.

Question 58

Bacterial mating (or conjugation) is a bidirectional process where nucleic acids (DNA or RNA) are transferred between two cells.

Answer 58

FALSE: Conjugation is primarily unidirectional, from the donor (usually F+ or Hfr) to the recipient (usually F-).

Question 59

Laboratory-based genetic systems have been difficult to develop for Archaea, because they do NOT naturally undergo conjugation or transduction.

Answer 59

TRUE: While it’s true that developing genetic systems for Archaea has been challenging, the statement about not undergoing conjugation or transduction is overly broad. Some Archaea can undergo these processes, but they are less well-characterized than in Bacteria.

Question 60

Almost all plasmids are double-stranded DNA.

Answer 60

TRUE: The vast majority of plasmids found in nature are indeed double-stranded circular DNA molecules.

Question 61

Most plasmids are circular rather than linear.

Answer 61

TRUE: In prokaryotes, most plasmids are circular, although linear plasmids can be found in some species, particularly in certain Archaea and Bacteria.

Question 62

When the F factor is integrated, all Hfr strains have the origin of replication functioning in the same direction.

Answer 62

FALSE: The orientation of the integrated F factor (and thus its origin of replication) can vary among different Hfr strains, leading to differences in the order and timing of gene transfer during conjugation.

Question 63

In a prokaryotic genome, either insertion elements OR transposons are present, but both are never present at the same time.

Answer 63

FALSE: This is an overly restrictive statement. Both insertion sequences (IS elements) and transposons (which often contain IS elements on their ends) can coexist within the same prokaryotic genome.

Question 64

The use of transposons to generate mutations is a convenient way to create bacterial mutations in the laboratory.

Answer 64

TRUE: Transposons are widely used as mutagenic tools in molecular biology for their ability to insert randomly into genomes, thereby generating mutants.

Question 65

Transposons can be found on many genetic elements, including plasmids, chromosomes, and viral genomes.

Answer 65

TRUE: Transposons are indeed found on various genetic elements, facilitating their spread within and across genomes.

Question 66

In transformation experiments using a variety of Bacteria, it has been noted that essentially all of the cells in a population can become competent.

Answer 66

FALSE: Natural competence (the ability to take up free DNA) varies widely among bacterial species, and even in naturally competent species, not all cells in a population are competent at the same time.

Question 67

In specialized transduction, virtually any genetic marker can be transferred from donor to recipient.

Answer 67

FALSE: Specialized transduction is limited to genes near the site of prophage integration in the donor bacterium, not virtually any genetic marker.

Question 68

In specialized transduction, as exemplified by lambda phage in E. coli, transduction occurs at high efficiency for only a restricted group of genes near the insertion site of lambda.

Answer 68

TRUE: This accurately describes the mechanism of specialized transduction, where the efficiency of gene transfer is highest for genes adjacent to the prophage.

Question 69

Many Bacteria isolated from nature are natural lysogens.

Answer 69

TRUE: Lysogeny is a common state for many bacteria in natural environments, providing them with potential virulence factors or other advantages.

Question 70

Lysogeny is essential for the virulence of many pathogenic bacterial strains.

Answer 70

TRUE: For numerous pathogens, the genes carried by prophages contribute significantly to their virulence.

Question 71

Proteins and nucleic acids absorb light maximally at 260 nm; hence, proteins protect cells from UV effects.

Answer 71

FALSE: While it’s true that nucleic acids absorb maximally at 260 nm, the statement about proteins absorbing maximally at this wavelength and thereby protecting cells from UV is incorrect. Proteins absorb maximally at 280 nm due to tryptophan, tyrosine, and phenylalanine.

Question 72

Insertion sequences are found on both ends of transposons and encode for transposase.

Answer 72

TRUE: Insertion sequences (IS) are indeed found on the ends of composite transposons. However, the transposase enzyme, which catalyzes the transposition, is encoded within the transposon itself, not necessarily within the IS elements, although some IS elements can encode their own transposase.

Question 73

Toxigenicity in Corynebacterium diphtheriae is due to phage conversion.

Answer 73

TRUE: The ability of C. diphtheriae to produce diphtheria toxin is conferred by a lysogenic phage, making this a classic example of phage conversion.

Question 74

All Hfr strains possess an F factor integrated into the host chromosome.

Answer 74

TRUE: By definition, Hfr (High Frequency of Recombination) strains have the F (fertility) plasmid integrated into their chromosome.

Question 75

Intercalating agents, like acridine orange and ethidium bromide, lead to mutagenesis by pushing DNA base pairs apart, which can lead to insertions or deletions.

Answer 75

TRUE: Intercalating agents work by inserting themselves between DNA base pairs, which can lead to frame-shift mutations (insertions/deletions) during DNA replication.

Question 76

A typical mutation rate for a bacterium is in the range of 10-6 to 10-7 per kbp.

Answer 76

TRUE: This range is generally accepted for the spontaneous mutation rate in bacteria, though it can vary depending on the species and conditions.

Question 77

Archaea have a unique form of conjugation involving cytoplasmic bridges for bidirectional transfer of DNA.

Answer 77

FALSE: While some Archaea can undergo conjugation-like processes, the description provided is more akin to bacterial conjugation mechanisms. Archaeal mechanisms can involve direct cell-cell contact but are less characterized and not typically described in these exact terms.

Question 78

A phage can be infectious even if all of its DNA has been replaced by bacterial DNA

Answer 78

FALSE: For a phage to be infectious, it must deliver its own genetic material (phage DNA) into a host to hijack the host’s machinery for replication. Replacing phage DNA with bacterial DNA would not achieve this.