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    who demonstrated that dna is the genetic material of the t2 phage?

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    Hershey–Chase experiment

    Hershey–Chase experiment

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    Overview of experiment and observations

    The Hershey–Chase experiments were a series of experiments conducted in 1952[1] by Alfred Hershey and Martha Chase that helped to confirm that DNA is genetic material.

    Scientist Alfred Hershey and Martha Chase

    While DNA had been known to biologists since 1869,[2] many scientists still assumed at the time that proteins carried the information for inheritance because DNA appeared to be an inert molecule, and, since it is located in the nucleus, its role was considered to be phosphorus storage. In their experiments, Hershey and Chase showed that when bacteriophages, which are composed of DNA and protein, infect bacteria, their DNA enters the host bacterial cell, but most of their protein does not. Hershey and Chase and subsequent discoveries all served to prove that DNA is the hereditary material.

    Hershey shared the 1969 Nobel Prize in Physiology or Medicine with Max Delbrück and Salvador Luria for their "discoveries concerning the genetic structure of viruses".[3]

    Contents

    1 Historical background

    2 Methods and results

    2.1 Experiment and conclusions

    3 Discussion 3.1 Confirmation

    3.2 Other experiments

    4 Legacy 5 References 6 External links

    Historical background[edit]

    In the early twentieth century, biologists thought that proteins carried genetic information. This was based on the belief that proteins were more complex than DNA. Phoebus Levene's influential "tetranucleotide hypothesis", which incorrectly proposed that DNA was a repeating set of identical nucleotides, supported this conclusion. The results of the Avery–MacLeod–McCarty experiment, published in 1944, suggested that DNA was the genetic material, but there was still some hesitation within the general scientific community to accept this, which set the stage for the Hershey–Chase experiment.

    Hershey and Chase, along with others who had done related experiments, confirmed that DNA was the biomolecule that carried genetic information. Before that, Oswald Avery, Colin MacLeod, and Maclyn McCarty had shown that DNA led to the transformation of one strain of to another. The results of these experiments provided evidence that DNA was the biomolecule that carried genetic information.

    Methods and results[edit]

    Structural overview of T2 phage

    Hershey and Chase needed to be able to examine different parts of the phages they were studying separately, so they needed to distinguish the phage subsections. Viruses were known to be composed of a protein shell and DNA, so they chose to uniquely label each with a different elemental isotope. This allowed each to be observed and analyzed separately. Since phosphorus is contained in DNA but not amino acids, radioactive phosphorus-32 was used to label the DNA contained in the T2 phage. Radioactive sulfur-35 was used to label the protein sections of the T2 phage, because sulfur is contained in protein but not DNA.

    Hershey and Chase inserted the radioactive elements in the bacteriophages by adding the isotopes to separate media within which bacteria were allowed to grow for 4 hours before bacteriophage introduction. When the bacteriophages infected the bacteria, the progeny contained the radioactive isotopes in their structures. This procedure was performed once for the sulfur-labeled phages and once for phosphorus-labeled phages. The labeled progeny were then allowed to infect unlabeled bacteria. The phage coats remained on the outside of the bacteria, while genetic material entered. Disruption of phage from the bacteria by agitation in a blender followed by centrifugation allowed for the separation of the phage coats from the bacteria. These bacteria were lysed to release phage progeny. The progeny of the phages that were labeled with radioactive phosphorus remained labeled, whereas the progeny of the phages labeled with radioactive sulfur were unlabeled. Thus, the Hershey–Chase experiment helped to confirm that DNA, not protein, is the genetic material.

    Hershey and Chase showed that the introduction of deoxyribonuclease (referred to as DNase), an enzyme that breaks down DNA, into a solution containing the labeled bacteriophages did not introduce any 32P into the solution. This demonstrated that the phage is resistant to the enzyme while intact. Additionally, they were able to plasmolyze the bacteriophages so that they went into osmotic shock, which effectively created a solution containing most of the 32P and a heavier solution containing structures called "ghosts" that contained the 35S and the protein coat of the virus. It was found that these "ghosts" could adsorb to bacteria that were susceptible to T2, although they contained no DNA and were simply the remains of the original viral capsule. They concluded that the protein protected the DNA from DNase, but that once the two were separated and the phage was inactivated, the DNase could hydrolyze the phage DNA.[1]

    Source : en.wikipedia.org

    Enterobacteria Phage T2

    Enterobacteria Phage T2

    As the T2 bacteriophage consists of only two components, they selectively labelled the DNA with radioactive 32P, and (in a separate batch) the proteins with 35S.

    From: Gene-Environment Interactions in Psychiatry, 2016

    Related terms:

    Nucleic AcidTobacco Mosaic VirusActinChitosan5-HydroxymethylcytosineNested GeneBacteriumBacteriophageEscherichia coliEnterobacteria Phage T4

    View all Topics

    DNA Topoisomerases: Biochemistry and Molecular Biology

    Wai Mun Huang, in Advances in Pharmacology, 1994

    IV T-Even Bacteriophage Topoisomerase Genes

    Escherichia coli bacteriophages T2, T4, and T6 encode a DNA topo II that is different from the host enzymes. These enzymes relax superhelical DNA in an ATP-dependent reaction, and they are incapable of introducing superhelical turns into the DNA. Furthermore, the coumarin and F-quinolone drugs are not effective inhibitors of the phage enzymes. The subunit structures of the T4 and T2/T6 enzymes are not the same. (T2 and T6 are nearly identical.) They represent a striking example of partitioning the encoding peptide into separate genes which clearly define the domains of the larger peptide. In T4 the enzyme is encoded by three genes, namely, 39, 60, and 52. The T4 39 protein has an ATPase activity, 52 is the cutting–rejoining unit, and 60 is required for tight complex formation between the 39 and 52 proteins (Huang, 1990). The derived amino acid sequences of the T4 genes can be aligned with those of the bacterial gyrB and gyrA genes: The T4 39 protein sequence (519 amino acids) can be aligned with the N-terminal portion of the GyrB protein and the T4 60 protein (160 amino acids) can be aligned with the C-terminal of the GyrB protein. The T4 52 protein (421 amino acids) is homologous to the N-terminal portion of the GyrA protein, which includes the region encompassing the reactive tyrosine residue where the transient protein–DNA bridge is formed during the DNA strand passage reaction. The topoisomerase genes are highly conserved among the three phages (higher than 85%), and the subunits are freely interchangeable. In T2 genes 39 and 60 are fused into one gene (605 amino acids), and it is equivalent to gyrB (Huang, 1990). The T2 39 gene, along with the 52 gene, encode the smallest topo II. These prokaryotic phage proteins share significant homology with the bacterial gyrase and the ParE and ParC proteins. However, like the ParE and ParC proteins, not all of the consensus amino acids identified in the gyrase alignment are found in the phage genes. Because the phage topo II activity is more akin to the eukaryotic enzymes, the sequence alignment is displayed in Fig. 3.

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    Fig. 3. Alignment of the topo II proteins. Sequences were from the GenBank data base. Critfa, Crithida fasiculata (Pasion et al., 1992); Trybru, Trypanosome brucei (Strauss and Wang, 1990); HuIIA, human Top2α (Tsai-Pflugfelder et al., 1988); HuIIB, human Top2β (C. A. Austin, J. H. Sng, S. Patel, and L. M. Fisher, personal communication); Dros2, Drosophila melanogaster (Wyckoff et al., 1989); Ytsc2, Saccharomyces cerevisiae (Giaever et al., 1986); Pomb2, Schizosaccharomyces pombe (Uemura et al., 1986); T2topo, bacteriophage T2 topoisomerase, which combines the 39 and 52 proteins (Huang, 1990); cons, consensus sequence for the cellular and T2 topo II proteins [does not include ASFV (African swine fever virus), which is shown below the cons line] (Garcia-Beato et al., 1992); * (in the 910 block), reactive tyrosine with which a covalent protein–DNA bridge is formed during the topoisomerization reaction; + (in the 610 block), junction where the T4 39 and 60 proteins fused to form the T2 39 protein; and + (in the 730–740 blocks), space between the T2 39 and 52 proteins.

    It is interesting to note that the amino acid residues of GyrA proteins which are most important for F-quinolone sensitivity (Section II,D,2), namely, the S83 and D87 residues, are different in the T-phage proteins. The critical residue, R136, which is responsible for coumarin sensitivity (Section II,D,1), is also different in the phage protein. These assignments are consistent with the observation that the phage topoisomerases are not sensitive to the gyrase-targeted antibiotics but are inhibited by antitumor drugs such as m-AMSA (Huang, 1990; Huff et al., 1989). When the T-phage proteins are correlated with the three-dimensional structure of the corresponding E. coli GyrB protein fragment, among the residues that are proposed to contact the triphosphate moiety, N46, Q335, and K337 are conserved and K103 is not; among those that contact the adenine ring, D73 is conserved and Y109 is not. The extensive sequence homology in the N-terminal 400 amino acids of the T2 39 protein with the gyrases seems to imply that the ATP-binding pocket may be similar, yet the fine details with which the phage protein interacts with ATP are not the same. This is also consistent with the known enzymatic properties of the enzymes, in that the phage proteins require ATP for DNA relaxation, whereas gyrases do not.

    Source : www.sciencedirect.com

    chapter 16 Flashcards & Practice Test

    Start studying chapter 16. Learn vocabulary, terms, and more with flashcards, games, and other study tools.

    chapter 16

    2.1 10 Reviews

    111 studiers in the last day

    mismatch repair of DNA (done by DNA polymerase 2)

    Click card to see definition 👆

    repair enzymes correct errors in base pairing

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    nucleotide excision repair

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    a nuclease cuts out and replaces damaged stretches of DNA

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    1/14 Created by fernandobot

    Terms in this set (14)

    mismatch repair of DNA (done by DNA polymerase 2)

    repair enzymes correct errors in base pairing

    nucleotide excision repair

    a nuclease cuts out and replaces damaged stretches of DNA

    mutations

    are source of new alleles (genetic variation upon which natural selection operates)

    linear chromosomes

    no way to complete 5' end as repeated rounds of replication produce shorter ends

    telomere

    -eukaryotic chromosomal DNA molecules have special nucleotide sequences at their ends

    -do not prevent shortening of DNA (postpone erosion of genes near DNA ends)

    -shortening of telomeres might protect cells from cancerous growth by limiting cell division

    telomerase

    catalyzes the lengthening of telomeres in germ cells (gametes)

    chromatin

    in eukaryotic cell DNA is precisely combined w proteins in chromatin complex

    [email protected] packed together into 10nm fiber

    euchromatin

    loosely packed chromatin

    heterochromatin

    -during interphase a few regions of chromatin (centromeres+telomeres) are highly condensed into heterochromatin

    -dense packing of heterochromatin makes it difficult for cell to express genetic info coded in regions

    Who demonstrated that DNA is the genetic material of the T2 phage?

    Hershey and Chase did a series of classic experiments demonstrating that DNA is the genetic material of the T2 phage.

    The radioactive isotope 32P labels the T2 phage's _____.

    The T2 phage consists of a protein coat and DNA. It is the DNA that contains P.

    The phage's protein coat is not labeled by P.

    Hershey and Chase used _____ to radioactively label the T2 phage's proteins.

    Hershey and Chase used radioactive sulfur to label the phage's proteins. Uranium is not a component of phages.

    After allowing phages grown with bacteria in a medium that contained 32P and 35S, Hershey and Chase used a centrifuge to separate the phage ghosts from the infected cell. They then examined the infected cells and found that they contained _____, which demonstrated that _____ is the phage's genetic material.

    Since the phage DNA entered the infected cell, it makes sense that DNA is the genetic material.

    A molecule does not have to be labeled in order to be the genetic material.

    helicase

    The role of helicases is to unwind the duplex DNA in order to provide a single-stranded DNA for replication, transcription, and recombination for instanc

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