Ch 7 - Bacterial and Viral Genetic Systems

As each bacterium grows and divides, it gives rise to a visible clump of genetically identical cells called. . . a broth. a colony. a complete medium. an agar.

a colony. After incubation for one to two days, bacteria multiply, forming visible colonies.

DNA from a strain of bacteria with genotype a+ b+ c+ d+ e+ was isolated and used to transform a strain of bacteria that was a− b− c− d− e−. The transformants were tested for the presence of donated genes. These genes were cotransformed: a+ and d+ b+ and c+ c+ and d+ c+ and e+. What is the order of genes a, b, c, d, and e on the bacterial chromosome? a, c, e, b, d e, d, c, b, a a, d, c, e, b a, c, d, e, b

a, d, c, e, b Gene a+ is cotransformed with gene d+, gene e+ is cotransformed with gene b+, gene c+ is cotransformed with gene e+.

What is the definition of an auxotroph? an organism that uses organic carbon in order to grow an organism that grows well in the absence of a required metabolite an organism that lacks the ability to synthesize a required metabolite an organism that produces complex compounds from simple compounds

an organism that lacks the ability to synthesize a required metabolite An auxotroph lacks the ability to synthesize a necessary metabolite that is required for its growth. The lack of synthesis means that the organism must be supplied with the metabolite from an external source in order to survive. For example, a strain of bacteria can be auxotrophic for the amino acid tryptophan, and thus unable to synthesize its own tryptophan. This mutant strain of bacteria is called a tryptophan auxotroph and must be supplied with tryptophan in the media in which it is grown in order to survive. A prototroph is an organism that can synthesize all of the metabolites needed for growth. A prototrophic bacteria would, therefore, be able to grow without being supplied metabolites in its media. When describing an ecosystem, there are several different similar terms that describe the broad type of organism. For example, an autotroph is also commonly called a producer because it can take very simple org

Generalized transduction by phage P1 of four E. coli genes (a, b, c, and d) shows these percentages of cotransduction: Gene transduction % Cotransduction a -- b 51% b -- c 2% b -- d 2% a -- d 40% a -- c 19% c -- d 79% What is the correct order of the four genes? b a d c a b c d b d a c d a c b

b a d c b and c have the lowest percentage of cotransduction.

The table shows the growth of various strains of bacteria on minimal and supplemented media. Note that a "+" indicates growth on the medium and "-" indicates no growth. Strain|Minimal|Min+Adenine|Min+Leucine|Min+Leu+Ad 1 + + + + 2 - - + + 3 - + - + 4 - - - + Which strain is not an auxotroph? 1 2 3 4

1 Strain 1 is considered to be a prototrophic bacteria, since it is able to grow on the minimal medium. Note: Strain 2 is an auxotroph for leucine.

Place the steps of bacterial transformation in order of occurrence. Not all items will be placed. DNA binds to the DNA-binding complex Enzymes separate double-stranded DNA into single strands A single-stranded fragment of DNA is important into the cell The DNA fragment of DNA is imported into the cell A phage injects DNA into bacteria

1. Bacteria encounters foreign DNA from the environment 2. Donor DNA binds to the DNA-binding complex 3. Enzymes separate double-stranded DNA into single strands 4. Single stranded fragment of DNA is imported into the cell 5. the DNA recombines into a homologous region of the bacterial chromosome 6. Foreign DNA is duplicated with bacterial DNA after the next round of cell division Bacteria incorporate DNA from the environment into their genomes through the process of transformation. This process is shown in the image. Bacterial transformation begins with the binding of a piece of free DNA to a DNA‑binding complex found on the bacterial surface. After the DNA is bound, enzymes dissociate the double‑stranded molecule into small, single‑stranded fragments. After the DNA is denatured, the single‑stranded DNA can be imported into the bacterial cell. Once the fragmented DNA is single‑stranded and inside the bacterial cell, the final step of bacterial transformation occurs.

Place the steps of generalized transduction in order of occurrence. Assume the bacteriophage (phage) enters a lytic cycle.

1. Phage binds to a bacterial surface 2. Phage injects viral DNA in host bacterial cell 3. Host DNA hydrolysis in pieces 4. Phage DNA is now replicated and new phage coat proteins are synthesized 5. The bacterial DNA is surrounded by phage coat protein 6. Host bacterial cell lyses 7. Bacterial DNA is injected into a bacterium by the phage One or more things Everything else 8. Bacterial DNA integrates into the new bacterial host chromosome ou may have not correctly placed some steps of generalized transduction. Remember, generalized transduction begins with the injection of phage DNA into a bacterium. The phage takes over the genetic machinery of the bacteria to replicate itself. Generalized transduction occurs when a mistake is made during the phage replication cycle such that bacterial DNA is encapsulated, rather than viral DNA, and that DNA is transferred to another bacteria. 1. Phage binds to a bacterial surface. 2. A phage injects viral DNA into a host bacterial cell. 3. Ba

If 1 million F- bacteria received an F factor through conjugation with F+ bacteria, how many of these would be expected to become Hfr bacteria?

100 (1 in 10,000 F- become Hfr)

Two mutations that affect plaque morphology in a particular phage (a- and b-) have been isolated. Phages carrying both mutations (a-b-) are mixed with wild-type phages (a+b+) and added to a culture of bacterial cells. Following infection and lysis, samples of the phage lysate are collected and cultured on bacterial cells. The numbers of plaques observed are as follows: Plaque Genotype Number a+b+ 1134 a+b- 176 a-b+ 192 a-b- 1023 What is the frequency of recombin

14.6% The recombination frequency is determined by dividing the recombinant progeny by the total progeny.

The table shows the growth of various strains of bacteria on minimal and supplemented media. Note that a "+" indicates growth on the medium and "-" indicates no growth. Strain|Minimal|Min+Adenine|Min+Leucine|Min+Leu+Ad 1 + + + + 2 - - + + 3 - + - + 4 - - - + Which strain is an auxotroph for leucine and a prototroph for adenine? 1 2 3 4

2 Strain 2 only requires the addition of leucine in order to grow and reproduce.

The table shows the growth of various strains of bacteria on minimal and supplemented media. Note that a "+" indicates growth on the medium and "-" indicates no growth. Strain|Minimal|Min+Adenine|Min+Leucine|Min+Leu+Ad 1 + + + + 2 - - + + 3 - + - + 4 - - - + Which strain is an auxotroph for adenine and a prototroph for leucine?

3 Strain 3 requires only the addition of adenine in order to grow.

A host range mutant strain (hr+) of phage T2 was mixed with a rapid lysis mutant strain (hr+r), and used with a high multiplicity of infection to infect E. coli B. The progeny from the cross were titered (counted) on a mixture of E. coli B and E. coli B/2 strains. These plaques were scored: hr+, 212; hr,114; h+ r+,106; h+r, 188. What is the approximate recombination frequency for these two loci? 35% 14% 24% 11%

35% The recombinant progeny divided by the total progeny will produce the recombination frequency.

In E. coli, a generalized transduction was carried out using a donor strain of a+ b+ c+ genotype. The recipient strain was a- b c-. 381 a+ transductants were first recovered, and then the remaining genotypes of these 381 were determined. The results are shown: Genotype Number of transductants a+b-c- 32 a+b+c- 9 a+b-c+ 0 a+b+c+ 340 What is the cotransduction frequency between a and b? 8.4% 58% 92% 68%

92% The second and fourth classes represent cotransduction of a and b. Two of the four transductant classes represent cotransduction of a and b.

Why can a genetically pure bacterial strain be isolated from a single colony of millions of cells? Several genetically diverse bacterial cells arise from the initial colony, but then one strain becomes predominant and takes over the colony; thus the resulting cells are genetically identical. A colony is made up of a single cell. When you "pick" a colony, you are only taking one cell from that colony to perform genetic analysis on. A colony is formed from a single bacterium that divides many

A colony is formed from a single bacterium that divides many times and, thus, all cells are genetically identical. Genetically pure strains can be isolated by collecting bacteria from a single colony and transferring them to a new broth tube or agar plate.

Most serious epidemics (pandemics) of influenza viruses are caused by new viral strains resulting from antigenic shifts. Which of these is the main reason why antigenic shifts can result in serious health problems? The enzyme that copies the RNA genome is not very accurate, and mutations will occur in progeny viral particles. A new and very different virus strain can be created, and very few individuals will have immunity to it. A provirus will integrate into the host genome and allow more pr

A new and very different virus strain can be created, and very few individuals will have immunity to it. Major changes in the viral genome occasionally take place through antigenic shift, in which genetic material from different strains is combined in a process called reassortment.

Which of the statements is false about the conjugation of an Hfr bacterium and an F- bacterium? A physical connection is formed between the Hfr and F- bacteria during conjugation. The single strand of DNA that enters the F- recipient is replicated by the F- bacterium's DNA replication enzymes. The Hfr bacterium's genes close to the leading sides of F origin of transfer are more likely to be transferred to the F- bacteria than those genes more distant to the leading side of the F origin of tra

After nicking the Hfr chromosome, the free 3' end moves through the transfer pore connecting the two bacteria as the chromosome replicates.

Which of the features are essential to map the bacterial chromosome in a single interrupted mating experiment? All of the features are essential when attempting to map the bacterial chromosome in a single interrupted mating experiment. Individual pairs of Hfr and F- bacteria must begin conjugation nearly simultaneously. One must be able to select against Hfr cells following conjugation. One must be able to remove aliquots of the conjugating bacteria and stop the mating at different time poi

All of the features are essential when attempting to map the bacterial chromosome in a single interrupted mating experiment.

Which statement about conjugation in bacteria is not true? Conjugation requires the presence of the F factor in one of the two participating cells. During conjugation, genes are transferred across a physical connection between two cells. Conjugation always results in an equal exchange of genetic material between two bacterial cells. Conjugation normally does not bring about transfer of the entire bacterial chromosome from one cell to another.

Conjugation always results in an equal exchange of genetic material between two bacterial cells. Conjugation involves transfer of genes in one direction only, from the donor to the recipient.

Suppose a researcher conducts mating between three Hfr bacterial strains of an F- strain. The table shows the order in which gene are incorporated for each strain. Determine the gene order of the chromosome by placing each gene on the outside of the circular chromosome map. Identify the origin of replication for each Hfr strain on the inside of the map to indicate polarity of the origin. Hfr strain: Order of gene transfer: 1 : ikvqw 2 : tzrbm 3 : vkimb

Conjugation experiments provide a simple method to experimentally map a circular bacterial chromosome. During mating, the Hfr strain begins to replicate its genome from the origin of replication and transfer its genetic material to the F− strain. Through homologous recombination, the genomic fragment from the Hfr strain can be integrated into the genome of the F− strain, producing exconjugants. Different strains of bacteria can have different origins of replication. Each sequence shown in the table represents a fragment of a complete circular genome containing marker genes. The markers that are closest to the origin of replication are replicated first and have more time to undergo homologous recombination and integrate into the F− genome. Therefore, the most frequently occurring markers from a given mating are likely to be closest to the origin of replication, and this principle informs the order of the genes in a given Hfr strain. When two fragment sequences share overlapping

Match each description to the appropriate type of horizontal gene transfer in bacteria. The union of to bacterial cells during which genetic material is transferred from the donor to the recipient The movement of genes into a bacterial recipient cell via a phage vector Free DNA in the extracellular environment taken up by bacterial cells

Conjugation: DNA is transferred from a donor to a recipient cell via a direct connection Transduction: DNA transfer medicated through the action of a bacterial virus Transformation: transfer of genetic material from the extracellular environment Conjugation, transduction, and transformation are three mechanisms by which genes can be transferred to a bacterial recipient cell. These three mechanisms help to generate genetic diversity in bacteria, which reproduce asexually. Upon the acquisition of donor DNA, the recipient cell uses homologous recombination to incorporate the donor DNA into its own genome. The recombinant bacteria then adopt the genotypic and phenotypic properties of the donor DNA. Conjugation is the process by which DNA is transferred from the donor cell to the recipient cell by a direct connection. The direct connection is mediated by a hollow protein structure called the pilus. The donor cell produces the pilus, which connects the donor cell to the recipient cell.

An Hfr bacterial strain with a genotype of amp^s, gal+, leu+, cys+, thr+ was used in an interrupted mating experiment with an F- bacterial strain with genotype amp^r, gal-, leu-, cys-, thr-. At regular intervals, the mating was interrupted and bacteria were selected with ampicillin and tested for the transfer of Hfr alleles into the F- bacteria. The time required to transfer the donor genes is shown in the table. Gene transferred Time cys. 3 min thr. 6 min gal. 10 m

Cys

Which of these crosses would be most useful for mapping the position of the lac gene on the bacterial chromosome? F-lac+ × F- lac- F+lac+ × F- lac- F' lac+ × F- lac- Hfr azir tonr gal+ lac+ × F- azis tons gal- lac-

Hfr azir tonr gal+ lac+ × F- azis tons gal- lac- Interrupted conjugation can be used in this mating to determine the time of transfer and the order of the genes on the chromosome relative to each other.

Which of the statements about the culturing and studying of bacteria is correct? The bacterial culture can continue to divide and the cell number will increase, as the cells are small and do not require many nutrients to grow and divide. Even though the auxotrophy for certain nutrients can limit bacterial growth, spontaneous mutation can occasionally allow bacteria to grow. Each bacterium that grows and divides gives rise to a visible clump of a bacterial colony, which displays a great deal o

Even though the auxotrophy for certain nutrients can limit bacterial growth, spontaneous mutation can occasionally allow bacteria to grow. The rate of spontaneous mutation is relatively high in bacteria especially under a stressful condition.

Austin Taylor and Edward Adelberg isolated some new strains of Hfr cells that they then used to map several genes in Escherichia coli by using interrupted conjugation. In one experiment, the researchers mixed cells of Hfr strain AB-312, which were xyl+ mtl+ met+ and sensitive to phage T6, with F- strain AB-531, which was xyl- mtl- met- and resistant to phage T6. The cells were allowed to undergo conjugation. At regular intervals, the researchers removed a sample of cells and interrupted conj

F - mal - xyl - mtl - met Mal + xyl = 7 min Xyl + mtl = 2 min Mtl + met = 9 min Scientists use interrupted conjugation experiments, such as the one described in this experiment, when mapping bacterial chromosomes. They determine the order of genes on the chromosome and their relative distances from one another by observing the time at which recombinant F− cells with the genes present first show up in their samples, which are taken at consistent intervals. The origin of transfer is the starting point from which the transfer of genes will begin. In the experiment, the first recombinants to appear at about 23 minutes contained only mal, and then seven minutes later recombinants containing the xyl gene were detected at 30 minutes. This means that mal is the first gene to be transferred and is closest to the origin point, whereas xyl is the second gene to be transferred, and they are seven minutes apart on the chromosome. Furthermore, xyl is followed about one minute later by mtl, at 3

Which mating in bacteria will allow for the formation of a strain that is partially diploid, lac+/lac-? F- lac+ × F- lac- Hfr lac+ × F-lac- F+lac+ × F-lac- F'lac+ × F- lac-

F'lac+ × F- lac- In this mating, the F' carrying lac+ will be transferred intact to the lac- recipient. After conjugation is complete, lac+ will be stably inherited on the F', and lac- will continue to be stably inherited on the recipient's chromosome.

Three pairs of bacterial cells with the given genotypes undergo conjugation. Place match the genotype of each cell after conjugation to its initial genotype. F+ x F-: Hfr x F-: F' x F-: What is the role of the F-factor in conjugation? • It contains genes that force recombination between the donor and recipient chromosomes. • It degrades the chromosome of the recipient cell after conjugation. • It allows auxotrophic bacterial cells to survive on minimal medium so that conjugation can occ

F+ x F-: F+ F+ Hfr x F-: Hfr F- F' x F-: F' F' • It contains genes necessary for the formation of the pilus • It contains genes necessary for replication of the donor's F plasmid. Bacterial conjugation is the process through which a donor cell, containing an F‑factor (F+), transmits genetic material to a recipient cell that does not have the F‑factor (F−). Transmission occurs through a pilus, a tube connecting the two cells, which is produced by the donor cell. The F‑factor may be present in a bacterial cell in different forms. Often, it is completely separate from the bacterial genome and exists on a plasmid with the cell, making the cell F+. When an F+ cell conjugates with an F− recipient cell, the recipient cell gains the F‑factor and becomes F+. Because the F plasmid is duplicated in the donor cell, the donor cell also remains F+, resulting in two F+ cells. In some cases, the F‑factor will be integrated completely into the bacterial chromosome, making the

Match each characteristic to the proper bacterial fertility factor type. F-, F+, F, Hfr Contains a plasmid with only the F factor Contains the F factor, but not in separate plasmid Recipient of DNA during bacterial conjugation Contains a plasmid with the F factor and some genomic DNA Does not contain the F factor sequences

F- Bacterium: recipient of DNA during bacterial conjunction, does not contain the F factor sequences F+ bacterium: contains a plasmid with only the F factor F' bacterium: contains a plasmid with the F factor and some genomic DNA Hfr Bacterium: contains the F factor, but not in a separate plasmid In the process of conjugation, a bacterium can transfer part of its DNA to another bacterium. The fertility (F) factor is a specific sequence of DNA that confers the ability to initiate conjugation by allowing the transfer of genes from one bacterium to another. A bacterium without the F factor, known as an F− bacterium, does not have the ability to initiate conjugation and serves as the recipient during conjugation. A bacterium with a plasmid containing only the F factor is known as a F + bacterium. A plasmid is a small, circular DNA molecule that is separate from the bacterial genome. Once an F + bacterium replicates and transfers its plasmid to an F− bacterium, the F− bacterium no

Each image depicts a type of gene transfer. Match the term for the type of gene transfer that each image depicts. Not all terms will be placed. Terms: Transduction Conjugation Vertical gene transfer Transformation

First: conjugation Second: transduction Third: transformation Horizontal gene transfer occurs between prokaryotes in the same generation. Transfer occurs between a donor cell and a recipient cell. The recipient cell receives genetic information from the donor in the form of naked DNA or plasmids. Three types of horizontal gene transfer are conjugation, transduction, and transformation. The first image depicts two bacteria that are joined together by a sex pilus. The red genome represents the genetic material from the donor cell, whereas the blue genome represents the genetic material from the recipient cell. There are also plasmids present in the donor cell. A plasmid is extrachromosomal DNA that replicates independently from the bacterial genome. One type of plasmid found in some bacteria is an F plasmid, which carries the information for pili formation. The image shows the transfer of the F plasmid from the donor cell to the recipient cell. This type of horizontal transfer is known

In the interrupted mating experiment shown in the animation, the strs allele from the Hfr strain enters the F- bacteria before the azi^r, lac+, and gal+ alleles. Why can you use streptomycin to select for F- recombinant bacteria if the first gene entering the F- bacteria can potentially convert the streptomycin resistant F- strain into a streptomycin sensitive bacterium? There must be some mistake in the experimental set up. The first gene entering an F bacterium is always incapable of underg

For linear DNA to recombine with the bacterial chromosome, a double crossover is required. Streptomycin dictates that the crossovers eliminate the str allele from the donor DNA without recombination.

Suppose scientists study mutant bacterial strain of Staphylococcus aureus to find the order of the genes for tetracycline resistance (gene T), streptomycin resistance (gene S) erythromycin resistance (gene E), and penicillin resistance (gene P). They extract DNA from bacterial strains with one or more of these mutations and transform wild-type bacterial cells (S+, E+, T+, P+) with the DNA. Given that the P mutation is first, indicate the order of these bacterial genes within the genome accordin

Gene P: T e S Transformation is a form of gene transfer. In natural transformation, bacterial cells have the ability to spontaneously take DNA fragments from the surrounding environment and insert it into their genomes. In the lab, scientists have the ability to induce transformation by making bacterial cell walls permeable in a process called artificial transformation. When donor DNA is extracted, it is fragmented into smaller pieces before being introduced to the recipient bacteria. Therefore, if there are two genes that are very close together, it is more likely that they will be transformed into a bacterial cell than if they were further apart. This concept is the basis of transformation analysis. During this type of experiment, however, the transformation efficiency is not 100%. Therefore, not all of the bacterial colonies will represent transformants. Because the recipient bacteria only take up small fragments of DNA during transformation, the closer two genes are together,

Interrupted conjugation is used to determine the order of gene transfer from a (n) ____ strain to F-. Hfr F' F+ F-

Hfr The times required for individual genes to be transferred indicate their relative positions on the chromosome.

Which can be accomplished by an interrupted mating experiment between Hfr and F- bacteria? Interrupted mating experiments can determine the genome size of the Hfr bacteria. Interrupted mating experiments can determine the physical distance between genes on the F- bacterial chromosome. Interrupted mating experiments can determine the DNA sequence of the Hfr bacterial chromosome. Interrupted mating experiments can determine the gene order on the F bacterial chromosome. Interrupted mating expe

Interrupted mating experiments can determine gene order on the Hfr bacterial chromosome.

Drugs that are used to treat HIV infection in humans include drugs that inhibit the activity of reverse transcriptase. What is likely the most direct effect of a reverse transcriptase inhibitor in treating HIV infections? It prevents the synthesis of a provirus. It increases the viral mutation rate. It prevents transcription of the provirus so new viral progeny cannot be produced. It blocks the entry of the virus into the cell.

It prevents the synthesis of a provirus. When viral DNA enters the nucleus and is integrated into the host chromosome, it forms a provirus. In this case the viral DNA cannot be formed due to the inhibitor.

If lac+ Hfr bacteria mated with a lac- F- bacteria in an interrupted mating experiment, the F- bacteria will only gain the ability to metabolize lactose if a copy of the lac+ gene recombines with the F- bacteria's chromosome. Why is recombination into the bacterial chromosome necessary?

Linear DNA is unstable in bacterial cells and unless the lac+ gene is recombined into the bacterial chromosome, it will be destroyed.

Classify whether each of the characteristics belong to the lytic cycle, lysogenic cycle, or both. the host DNA is degraded the bacterial cell wall is broken open the bacterial genome contains the integrated phage genome the phage genome enters the host cell the phage genome replicates with the host DNA

Lytic: the host DNA is degraded the bacterial cell wall is broken open Lysogenic: the phage genome replicates with the host DNA the bacterial genome contains the integrated phage genome Both: the phage genome enters the host cell The lytic and lysogenic cycles are two alternative replicative mechanisms by which bacterial viruses, or bacteriophages, reproduce. The lytic cycle involves the reproduction of the phage and the destruction of the host cell. The lysogenic cycle involves the replication of the phage genome without damaging the host cell. A temperate phage is capable of reproducing through both the lytic and lysogenic cycle. During the lytic cycle, the phage first adheres to the outer surface of the host cell. The phage genome then enters the host cell. The phage DNA harnesses the host cell machinery to replicate the phage genome and synthesize phage proteins. Simultaneously, the host DNA is degraded to provide nucleotides for the synthesis of new phage genomes. New phage

A generalized transduction experiment is set up so that a phage is carrying a donor strain with the genotype met bio' thr'. This donor strain is used to transduce a recipient E. coli strain with the genotype met- bio- thr-. After transduction, the recipient population is plated on a minimal medium containing only organic salts and a simple carbon source supplemented with methionine and biotin. A large number of colonies are obtained. The wild-type genes indicate the bacteria do not need a supp

Met+ Bio- thr+ Met- Bio+ thr+ Generalized transduction is the transfer of a host bacterial chromosome by a phage into another bacterial cell. The DNA transferred by the phage can recombine with the bacterial DNA in the recipient cell, producing a recombinant bacterium with potentially different combinations of genes. Colonies of bacteria can be selected for specific genotypes using the plated medium. The mutant genes met−, bio−, and thr− cannot grow without supplemental methionine, biotin, or threonine, respectively. If the necessary vitamins or amino acids are not added to the minimal medium, some genotypes cannot grow, which results in selection for the bacterial genotypes that can grow on the prepared medium. In the question, the met+ bio+ thr+ DNA recombines with the met− bio− thr− strain in the transduction experiment to produce eight total genotypes. However, any recombinant bacteria containing the thr− genotype will not produce bacterial colonies because these E

Why is the number of described bacteria so low, historically, compared to other organisms such as plants? The genomes of bacteria cannot be sequenced; therefore the species diversity remains underestimated. Bacteria are too small to see; thus they have not been described. There are far more species of plants than bacteria on Earth. Most bacteria do not grow in culture; thus they have historically been underrepresented.

Most bacteria do not grow in culture, thus they have historically been underrepresented. Species of bacteria are typically described only after they have been cultivated and studied in the laboratory.

What are auxotrophs? Media that contains all the substances required by bacteria for growth. Mutant strains that lack one or more enzymes necessary for synthesizing essential compounds. Media that contains only the nutrients required by prototrophic bacteria. Bacteria that can use simple ingredients to synthesize all the compounds.

Mutant strains that lack one or more enzymes necessary for synthesizing essential compounds. Auxotrophs lack one or more enzymes necessary for synthesizing essential compounds, and will grow only on medium supplemented with those essential molecules.

Prokaryotes may contain both plasmid and chromosomal genomes. Classify each description as a characteristic of prokaryotic plasmids, prokaryotic chromosomes, or both. Usually circular in shape Used as a vector in biotechnology Holds genes required for survival Located in nucleoid region Enters cells by horizontal gene transfer Consists of double-stranded DNA Has a small selection of additional genes Usually transferred through a sex pilus Replicates only during prokaryotic fission

Plasmids only: Has a small selection of additional genes Usually transferred through a sex pilus Used as a vector in biotechnology Enters cells by horizontal gene transfer Chromosomes only: Holds genes required for survival Located in nucleoid region Replicates only during prokaryotic fission Characteristics of both: Usually circular in shape Consists of double-stranded DNA In addition to a chromosomal genome, prokaryotes frequently contain one or more extra pieces of DNA called plasmids. Both prokaryotic chromosomes and plasmids have DNA in the form of a double helix. As in eukaryotes, the prokaryotic DNA is composed of nucleotides arranged into gene sequences. The majority of prokaryotic chromosomes and plasmids are circular in shape. The prokaryotic chromosome is the cell's primary DNA and contains all of the essential genes for survival and reproduction. There is generally only one chromosome in a prokaryotic cell, and it is located in the cell's nucleoid region. When prokaryot

Two mutations that affect plaque morphology in phages (a and b) have been isolated. Phages carrying both mutations (a- b-) are mixed with wild-type phages (a+ b+) and added to a culture of bacterial cells. Subsequent to infection and lysis, samples of the phage lysate are collected and cultured on bacterial cells. The numbers of plaques are observed in the table. Using the data given in the table, calculate the recombination frequency between the a and b genes. Plaque phenotype: Number: a+b

Recombination frequency: 14 % When bacteriophages are added to a culture of bacterial cells growing on an agar plate, the phages are able to reproduce by infecting and lysing the bacterial cells in the region. The bacterial death produced is visualized as plaques, clear areas of no growth, where the bacterial culture was lysed. In this case, the plaque counts provide insight into the recombination frequency between the two genes of interest. The nonrecombinant classes of progeny include the a+ b+ and the a− b− classes since the phenotypes are identical to the original strains used in the initial mating. The recombinant classes, a+ b− and a− b+, are the unique phenotypes relative to the phenotypes of the original strains. The recombination frequency (rf) between a and b is calculated using the equation 𝑟𝑓=recombinants/total progeny × 100 = 320 + 357/(2043 + 320 + 357 + 2134) × 100 = 14%

How are Hfr strains of bacteria different from F+ strains? The F factor is integrated into the bacterial chromosome in all (or most) cells of an Hfr strain but in only a few cells in an F+ strain. Hfr strain cells carry F' plasmids while F+ cells do not. Hfr strains are able to transfer chromosomal genes while F+ strains cannot. Hfr strains cannot initiate conjugation with F- cells.

The F factor is integrated into the bacterial chromosome in all or most cells of an Hfr strain but in only a few cells in an F+ strain. An Hfr strain is derived from an Hfr cell by replication and binary division. Therefore, all (or most) of the cells will retain the integrated state of the F factor.

What best describes the most common fate of an F- bacterium after conjugation with an Hfr bacterium?

The F- bacterium remains F- but might also undergo a phenotypic change resulting from recombination.

Which of the statements about culturing bacteria is NOT true? The bacteria can be grown on a solid medium prepared with agar as well as liquid medium. The concentration of metabolic waste and depletion of nutrients eventually leads to the decline of bacterial growth in the culture. The bacterial cells, once inoculated, can indefinitely grow and divide in the sterile liquid medium. In order to cultivate the bacteria of your interest, a sterile medium must be prepared to avoid contamination.

The bacterial cells, once inoculated, can indefinitely grow and divide in the sterile liquid medium. Bacterial cells grow and divide until all the nutrients are used up, or until the concentration of their waste products becomes toxic to them.

An Hfr bacterial strain with a genotype of amp^s, gal+, leu+, cys+, thr+ was used in an interupted mating experiment with an F- bacterial strain with genotype amp^r, gal-, leu-, cys-, thr-. At regular intervals, the mating was interrupted and bacteria were selected with ampicillin and tested for the transfer of Hfr alleles into the F- bacteria. The time required to transfer the donor genes is shown in the table. Gene transferred Time cys. 3 min thr. 6

The distance between thr and gal is greater than the distance between gal and leu.

Match each image to the appropriate stage of the phage lytic cycle.

The phage lytic cycle is the process by which a phage infects a bacterial host cell and replicates. The phage lytic cycle has five distinct stages. The first stage in the phage lytic cycle involves the attachment of the phage to the bacterial host cell. Each phage has multiple regions on its surface that recognize and bind to receptors on the bacterial host cell surface. The second stage in the phage lytic cycle involves the injection of the phage genetic material into the bacterial host cell. The genetic material can be either DNA or RNA, and it codes for a number of proteins that allow the phage to replicate using the bacterial host cell's replication, transcription, and translation machinery. In addition, the phage genome codes for the proteins required to assemble more phage particles, such as capsid proteins. The third stage in the phage lytic cycle involves the replication of the phage genome. During replication, many copies of the phage genome are generated using the host cel

Why do bacteria and viruses have immense medical significance? They cause many human diseases. Bacteria and viruses play critical roles in agriculture. Bacteria remove roughly 50% of the carbon dioxide. Bacteria in the oceans produce 50% of the oxygen in the air.

They cause many human diseases. Bacteria and viruses have immense medical significance because they cause many human diseases.

Which of the statements is TRUE regarding plasmids? They are composed of RNA. They contain an origin of replication. They possess only a single strand of DNA. They normally exist outside of bacterial cells.

They contain an origin of replication. Each plasmid possesses an origin of replication, a specific DNA sequence where DNA replication is initiated.

Suppose DNA from a strain of Bacillus subtilis with the genotype a+ b+ c+ d+ e+ was used to transform a strain with the genotype a-b-c-d-e-. The pairs of genes were then checked for cotransformation and the data below was collected. Pairs of genes: a,b\a,c\a,d\a,e\b,c\c,d\b,e\c,d\c,e\d,e Cotransformation: no\no\yes\yes\yes\no\yes\no\yes\no

b+ end c+ e+ a+ d+ End of chromosome Cotransformation is the process wherein genes that are close together on a chromosome are transformed together. The greater the distance between two genes, the less likely it is that both genes will be transformed together from the donor DNA molecule to the recipient cell. Conversely, genes that are farther apart on the chromosome are less likely to cotransform. By examining all possible gene pairs, it is then possible to determine the order of genes on the chromosome. You are provided with the b gene as a reference point, so start by examining the various gene pairs that include the b gene. The gene pairs of b c, b e, and c e showed cotransformation, so either c or e is closest to b. Because the c gene shows cotransformation with no other gene, it is likely that c is in between b and e. To determine the remaining gene order, examine the gene pairs that include e. Gene e cotransformed with gene a, so the a gene likely comes next, leaving only

Evidence now points to a number of similarities and parallels in bacterial and eukaryotic structure. All of the statements are examples that support this fact EXCEPT. . . a bacterial protein termed FtsZ plays an integral part in bacterial cell division and is structurally similar to eukaryotic tubulin proteins. bacteria have proteins that help condense DNA. bacterial proteins function much as cytoskeletal proteins do in eukaryotes. bacteria undergo mitosis and meiosis to ensure that one copy

bacteria undergo mitosis and meiosis to ensure that one copy of the chromosome is allocated to each daughter cell. Bacteria replicate by means of binary fission as opposed to mitosis and meiosis

An Hfr bacterial strain with a genotype of amp^s, gal+, leu+, cys+, thr+ was used in an interrupted mating experiment with an F- bacterial strain with genotype amp^r, gal-, leu-, cys-, thr-. At regular intervals, the mating was interrupted and bacteria were selected with ampicillin and tested for the transfer of Hfr alleles into the F- bacteria. The time required to transfer the donor genes is shown in the table. Gene transferred Time cys. 3 min thr. 6 min gal. 10 m

both leu gal thr cys and cys thr gal leu are correct

In gene mapping using generalized transduction, bacterial genes that are cotransduced are. . . on different bacterial chromosomes. on a plasmid. far apart on the bacterial chromosome. close together on the bacterial chromosome.

close together on the bacterial chromosome Only genes located close together on the bacterial chromosome will be transferred together, or cotransduced.

Bacterial genes are more likely to be cotransduced in generalized transduction mapping experiments if they are close together on the bacterial chromosome. far apart on the bacterial chromosome. near the origin of replication on the bacterial chromosome. both located on a plasmid.

close together on the bacterial chromosome. Recombination frequencies can be used to determine the distances between genes and their order on the phage chromosome, just as they are used to map genes in eukaryotes.

Two different strains of a mutant phage infected a single bacterium. One phage strain is d-e+, and the other is d+e-. The phages go through the lytic cycle and produce progeny. What will be the recombinant genotypes in the progeny? d+e+ and d+e- d-e+ and d+e+ d-e+ and d+e- d+e+ and d-e-

d+e+ and d-e- Both of these genotypes are distinct from the parental phage strains, so the must be produced via recombination.

Which one of the viral genes encode the glycoproteins that appear on the surface of the virus? nef gag env pol

env The env gene encodes the glycoproteins that are found on the surface envelope of the virus.

Genes that are _____ are unlikely to be present on the same DNA fragment and are _____. far apart; rarely cotransformed close together; cotransformed isolated; transferred close together; not transferred

far apart; rarely cotransformed Genes that are far apart are unlikely to be present on the same DNA fragment and are rarely cotransformed.

Interrupted conjugation was used to map three genes in E. coli. The donor genes first appeared in the recipient cells at these times: gal, 10 minutes; his, 8 minutes; pro, 15 minutes. Which gene is in the middle? his gal his and pro pro

gal The amounts of time required for individual genes to be transferred from the Hfr to the F− cells indicate the relative positions of the genes on the bacterial chromosome.

If a bacterium requires glucose and nitrogen to grow and reproduce, what ingredients would you choose to dissolve in water to make a minimal medium for this species? none-water only glucose and nitrogen amino acids glucose

glucose and nitrogen A medium that contains only the nutrients required by prototrophic bacteria is termed a minimal medium, which in this case, is glucose and nitrogen.

A mapping study was done with the E. coli genes e, f, g and h using generalized transduction. The frequency of cotransduction was determined for pairs of genes as shown. Genes % Cotransduction eg 18 eh 4 fg 31 fh 2.7 gh 0 What is the most probable order for the four genes? h-e-g-f e-g-f-h h-e-f-g e-h-g-f

h-e-f-g h and g are the furthest apart having a 0% cotransduction percentage.

The relative rates at which pairs of genes are cotransformed indicate the distance between them. The _____ the rate of cotransformation, the _____ the genes are on the bacterial chromosome. higher; closer lower; closer lower; farther apart higher; farther apart

higher; closer Genes that are physically closer together on the bacterial chromosome are more likely to be present on the same DNA fragment and transferred together.

Bacterial strain with genotype his− leu− thr− is transformed with DNA from a strain that is his+ leu+ thr+. A few leu+ thr+ cells and a few his+ thr+ cells are found, but no his+ leu+ cells are observed. Which genes are the farthest apart? thr+ leu+ leu+ thr+ his+ thr+ his+ leu+

his+ leu+ Genes that are far apart are unlikely to be present on the same DNA fragment and are rarely cotransformed. NOTE; Genes that are physically closer together on the bacterial chromosome are more likely to transferred together. Genes that are physically closer together on the bacterial chromosome are more likely to be present on the same DNA fragment.

In which bacteriophage life cycle does the phage DNA become incorporated into the bacterial chromosome? haplontic lysogenic lytic diplontic

lysogenic The lysogenic cycle begins like the lytic cycle but, inside the cell, the phage DNA integrates into the bacterial chromosome.

Which of the viral genes encode proteins that are essential for achieving the provirus stage within the host cell? gag pol env nef

pol The pol gene encodes reverse transcriptase and integrase, which are needed for provirus formation. The gag gene encodes viral coat proteins.

The process of genetic _____ has been most critical in the evolution of HIV-1 and HIV-2 from simian immunodeficiency viruses found in chimpanzees and sooty mangabeys, respectively. replication recombination retrotranscription transcription

recombination HIV illustrates the importance of genetic recombination in viral evolution.

What enzyme is used by a retrovirus to make a DNA copy of its genome? polymerase reverse transcriptase integrase protease

reverse transcriptase A retrovirus uses reverse transcriptase to copy its RNA genome into a single-stranded DNA molecule.

An Hfr bacterial strain contains the genes a+, b+, c+, d+, f+, and strS in an unknown order. An F- bacterial strain contains the genes a,b,c,d,f, and strR also in an unknown order. The Hfr bacterial strain is mated with the F- strain. The mating is interrupted at different time points, and samples are plated onto selective media to assay for gene function. The frequencies of each recombinant are shown. Determine the linear order of genes of the Hfr chromosome using strR as a reference point.

strR: Gene 1: d+ Gene 2: c+ Gene 3: a+ Gene 4: f+ Gene 5: b+ Bacterial cells have two different mating types and can transfer DNA from one cell to another. The Hfr strain replicates a portion of its DNA and transfers the segment to the F− strain, starting with the F region. Only a portion of the circular chromosome is replicated, however the actual segment incorporated into the F− strain depends on where recombination occurs. Homologous recombination must occur on both sides of a gene in order to incorporate it into the recipient genome. Therefore, genes that are close together are more likely to be transferred together, whereas genes that are far part are more likely to be separated by recombination. Recombinant bacteria are selected by interrupting the mating between the Hfr and the F− strains and plating onto selective media. The position of strR is given, and the remaining genes can be ordered based upon the frequency with which they occur together with strR in the recombi

Rarely, the conjugation of Hfr and F− cells produces two Hfr cells. How can this event take place? by conjugating one Hfr cell and one F− the F factor is nicked in the middle of the initiation of strand transfer the recipient cell must receive the entire F factor In most cases, the only genes transferred during conjugation between an F+ and F− cell are those on the F factor

the recipient cell must receive the entire F factor The recipient cell must receive the entire F factor, requiring the entire donor chromosome be transferred.

Bacteriophages are ideal for many types of genetic research because of all of these, EXCEPT. . . produce large numbers of progeny. they come in a great variety of shapes and sizes. reproduce rapidly. they have small and easily manageable genomes.

they come in a great variety of shapes and sizes. This is a property of bacteria as opposed to viruses.

In the replica plating experiment, which bacterial colony on the original plate with complete media would you choose if you wanted to study an auxotroph for adenine? This is an illustration of media when exposed to different media components. On the left, there are four colonies that are present when a complete media is used. On the top right, when using minimal media - adenine, there are three colonies present on the plate. On the bottom right, when using minimal media + adenine, there a

top right colony Since the top right colony did not survive in the absence of adenine, it is considered an autotroph for that compound.

_____ normally takes place between bacteria of the same, or closely related, species only. Transduction Conjugation Replication Transformation

transduction Most bacteriophages have a limited host range, so transduction normally takes place between bacteria of the same or closely related species only.

What type of bacterial gene transfer involves a virus? conjugation transformation and transduction transduction transformation

transduction Transduction takes place when bacterial viruses carry DNA from one bacterium to another.

Which process of DNA transfer in bacteria requires a virus? transformation transduction replication conjugation

transduction Transduction takes place when bacterial viruses carry DNA from one bacterium to another.

How can the efficiency of transformation of bacteria be increased? spreading a dilute solution of bacteria over the surface of the agar the widespread use of antibiotics treatment with calcium chloride, heat shock, or an electrical field spreading bacteria on a petri plate containing medium that includes leucine

treatment with calcium chloride, heat shock, or an electrical field Treatment with calcium chloride, heat shock, or an electrical field makes bacterial membranes more porous and permeable to DNA.

In order to determine the original concentration of phage in the solution, what is the information required? volume of phage containing solution and number of plaque the number of bacterial colonies and volume of bacterial culture the number of plaques and the number of bacterial colonies the count of bacterial cells and phages used

volume of phage containing solution and number of plaque The original concentration of phage can be deduced from the known volume of a dilute solution of phages used and the number of plaques counted.