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Suppose you wanted to study genes controlling the structure of bacterial cell surfaces. You decide to start by isolating bacterial mutants resistant to infection by a bacteriophage that binds to the cell surface. The selection procedure is simple: Spread cells from a culture of sensitive bacteria on a petri plate, expose them to a high concentration of phages, and pick the bacterial colonies that grow. To set up the selection you could (1) spread cells from a single liquid culture of sensitive bacteria on many different plates and pick every resistant colony; or (2) start many different cultures, each grown from a single colony of sensitive bacteria, spread one plate from each culture, and then pick a single mutant from each plate. Which method would ensure that you are isolating many independent mutations?
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- Materials In order to determine the genetic material of a T2 phage, Alfred Hershey and Martha Chase conducted experiments using T2 phages that infected bacteria. In one treatment, they grew phages with radioactive sulfur. In another treatment, they grew phages with radioactive phosphorous. They allowed both types of phages to infect bacterial cells. After infection, they found that only bacteria infected with phages grown with radioactive phosphorous showed any radioactivity. Why did they use radioactive sulfur and phosphorous for this Updates Grades Members O Conferences DBQ Online experiment? * Newsela ormation O Sulfur is part of the DNA molecule but not part of a protein molecule. Biology Periods 1 and 2 Sulfur and phosphorous are some of the most reactive molecules and are easily ding periods school MP1, Highschool Highschool MP3, school MP4 traced. Sulfur and phosphorous are able to survive the centrifuge, a crucial component of the experiment. ion Phosphorous is part of the DNA…arrow_forwardIn transformation, a bacterial cell takes up DNA fragments from its surroundings. The figure shows the process of natural transformation. Position the labels below with the correct images. (A) Donor and recipient genomes The donor strand is integrated into the recipient chromosome and the displaced bacterial DNA is degraded. A wild-type donor cell is in the vicinity of a double auxotroph. If the wild-type cell lyses, it releases DNA into the environment. One cell is identical to the original recipient, while the other carries the wild-type genes. A competent recipient cells a receptor site on its surface. One strand of donor DNA enters the cell and pairs with a homologous region of the bacterial chromosome The remaining DNA strand is degraded. A donor DNA strand binds to the receptor site. Reset trpC1 Wild-type donor cell Mechanism of natural transformation Donor DNA hal Receptor site- trpc/his double auxotroph Recipient cell Competent cell recipient -Bacterial chromosome (had.bpC") Ma…arrow_forwardImagine that you are a student in Alfred Hershey and Martha Chase’s lab in the late 1940s. You are given five test tubes containing E. coli bacteria infected with T2 bacteriophages that have been labeled with either 32P or 35S. Unfortunately, you forget to mark the tubes and are now uncertain about which were labeled with 32P and which with 35S. You place the contents of each tube in a blender and turn it on for a few seconds to shear off the phage protein coats. You then centrifuge the contents to separate the protein coats and the cells. You check for the presence of radioactivity and obtain the following results. Which tubes contained E. coli infected with 32P-labeled phage? Explain your answer. Tube number Radioactivity present in 1 Cells 2 Protein coats 3 Protein coats 4 Cells 5 Cellsarrow_forward
- In a genetics lab, Kim and Maria infected a samplefrom an E. coli culture with a particular virulent bacteriophage. They noticed that most of the cells werelysed, but a few survived. The survival rate in theirsample was about 1 × 10−4. Kim was sure the bacteriophage induced the resistance in the cells, whileMaria thought that resistant mutants probably alreadyexisted in the sample of cells they used. Earlier, for adifferent experiment, they had spread a dilute suspension of E. coli onto solid medium in a large petri dish,and, after seeing that about 105colonies were growingup, they had replica-plated that plate onto three otherplates. Kim and Maria decide to use these plates totest their theories. They pipette a suspension of thebacteriophage onto each of the three replica plates.What should they see if Kim is right? What shouldthey see if Maria is right?arrow_forwardImagine that you are a student in Alfred Hershey and Martha Chase’s lab in the late 1940s. You are given five test tubes containing E. coli bacteria infected with T2 bacteriophages that have been labeled with either 32P or 35S. Unfortunately, you forget to mark the tubes and are now uncertain about which were labeled with 32P and which with 35S. You place the contents of each tube in a blender and turn it on for a few seconds to shear off the phage protein coats. You then centrifuge the contents to separate the protein coats and the cells. You check for thepresence of radioactivity and obtain the following results. Which tubes contained E. coli infected with 32P-labeled phage? Explain your answer.arrow_forwardYou have found that two types of bacteria (one large, one small) can undergo horizontal gene transfer. The smaller cells encode the green fluorescent protein (GFP), and the large cells do not glow. You mix the two types of cells together, and allow them to grow together on an agar plate. The next day, you find that some of the larger cells have acquired the gfp gene and now glow green, indicating that the gene has moved from the smaller cells to the larger cells. You want to determine whether this is occurring via conjugation, transformation, or transduction. You have available a few different experimental tools: -Pure cultures of the large, non-glowing bacteria -Pure cultures of the small, gfp-expressing, glowing bacteria -0.2 µm filters (will trap both types of cells, but will let other smaller materials through) -DNase enzyme (degrades DNA) -Fluorescent microscopes and electron microscopes -All other necessary test tubes, liquid growth media, agar plates, etc Briefly outline a…arrow_forward
- Assume that there are horizontal gene transfers between two completely different bacterial species. In one case it is a plasmid that is transmitted via conjugation, in the other case it is it is a part of the bacterial chromosome that is transferred via transformation. In which of the two cases is it likely that the transferred DNA will be present? left and can function in the recipient cells? Explain the biological background to your answerarrow_forwardIn the experiment below, flasks of human fibroblasts are either transfected with a control gene or the v-src gene. After 48 hrs the flasks (Top row) as well as microscope images of cells on surface of flask (bottom row) from the two different experiments are depicted. Which Flask (A or B) is from the v-src transfection? Justify in 3-4 sentences why you drew this conclusion. Flask A Flask B iumarrow_forwardImagine that there is an E. coli outbreak in your area, and you would like to test the kangkong from your local grocery store. How could you modify this protocol to extract DNA from the kangkong (to identify the species) and check for presence or absence of E. coli.? Keep in mind that (i) E. coli is free-living and not an endosymbiont, and (ii) plant cells are encased in both a cell membrane and cell wall.arrow_forward
- Imagine that you are a student in Alfred Hershey and Martha Chase’s lab in the late 1940s. You are given five test tubes containing E. Coli bacteria infected with T2 bacteriophages that have been labeled with either 32P or 35S. Unfortunately, you forget to mark the tubes and are now uncertain about which tubes is which. You performed their blender experiment and got the following results. Which tube out of these 5 contains E. Coli infected with 32P-labeled phage? Explain your answer.arrow_forwardBacterial conjugation has medical consequences. For example, certain plasmids contain genes that code for toxins. The causative agent of a deadly form of food poisoning, E. coli 0157, synthesizes a toxin that causes massive bloody diarrhea and kidney failure. This toxin is now believed to have originated in Shigella, another bacterium that causes dysentery. Similarly, the growing problem of antibiotic resistance is partly attributable to the spread of antibioticresistant genes among bacterial populations. Antibiotic resistance develops because antibiotics are overused in medical practice and in livestock feeds. Suggest a mechanism by which this extensive use promotes antibiotic resistance.arrow_forwardFour different types of molecules, namely A, B, C and D were isolated from a primitive life form and studied to determine which of these would have the characteristics of an ancient genetic material. The molecules were incorporated into vectors, which are the phages whose genome were transformed into recombinant DNA. The phages were then made to infect the host bacteria. Transfection with A increased bacterial motility; B resulted in the formation of a pili allowing bacteria to adh to surfaces; causes the overproduction of a membrane protein while D resulted in increased metabolism of the bacterial food source, glucose. Which of the molecules is most likely a genetic material for this primitive life form? А. А В. В С. С D. D E. all of thesearrow_forward
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