Concept explainers
Bacterial transformation and bacteriophage labeling experiments proved that DNA was the hereditary material in bacteria and in DNA-containing viruses. Some viruses do not contain DNA but have RNA inside the phage particle. An example is the tobacco mosaic virus (TMV) that infects tobacco plants, causing lesions in the leaves.
Two different variants of TMV exist that have different forms of a particular protein in the virus particle that can be distinguished. It is possible to reconstitute TMV in vitro (in the test tube) by mixing purified proteins and RNA. The reconstituted virus can then be used to infect the host plant cells and produce a new generation of viruses. Design an experiment to show that RNA, rather than protein, acts as the hereditary material in TMV.
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Chapter 6 Solutions
Genetics: From Genes to Genomes
- Assume you isolate a single stranded (+) RNA virus. When you examine the proteins in the virus, you find that it does NOT contain replicase enzymes within its capsid. Which of the following is true? This virus must have a gene that encodes replicase. This virus will not be able to enter a host cell. Its genome cannot be translated (the process of translation) by the host cell ribosomes. A DNA copy of the viral genome has to be made before viral genes are expressed. This virus must lack surface antigens.arrow_forwardSome retroviruses that have a wide host range have been developed for use in treatment of diseases or syndromes. These viruses do not result in a productive infection because they lack critical genes for viral replication, but they do carry DNA sequences that allow them to be packaged into infectious particles. Once in the host cell the viral DNA is released and integrates into the cell's genome. The advantage to this strategy is that the delivery of the DNA is very efficient. What is one possible problem of using a virus that can integrate into the human nuclear genome? Multiple Choice The virus carries genes that will interfere with host cell activities. The viral DNA sequences could still cause a disease. Since the viral DNA sequences no longer contain essential genes for viral replication the host cell may not be able to replicate either. The integration could disrupt an essential gene or genes.arrow_forwardViruses are host-specific, meaning they can only infect specific types of host organisms. For examble, the adenovirus is responsible for the common cold in humans but your dog can't catch a cold from you. Why is this? The proteins on the virus surface can only bind with proteins on the correct host surface. It is an enveloped or non-enveloped virus. The enzymes carried by the virus are compatible with the host. The genome of the virus is made of DNA or RNA.arrow_forward
- The table below shows the properties of the genomes of three different viruses. The data were obtained as follows: Nuclease sensitivity was measured by the ability of deoxyribonuclease (DNase) or ribonuclease (RNase) to destroy the genome (a “+" means sensitivity). The ability of the genome to act as mRNA was tested by incubating it in a cell-free system. If amino acids were incorporated into protein, the data are shown as a Finally, the virus particles were tested for the presence of a virion polymerase. If an enzyme was present, the data show whether it could polymerize deoxynucleotide triphosphates (DNTPS) or nucleoside triphosphates (NTPS). "+. Genome Properties Nuclease Virion Can Genome Sensitivity? Polymerase? Be an mRNA? Virus DNase RNase With With DNTPS NTPS #1 - - #2 - - #3 For each virus, indicate the strategy of the genome, using the Baltimore classification. What is the nature of the product of the virion polymerase when present? + + + + + +arrow_forwardOne of the reasons why phage therapy has not been applied widely is that bacteria can become resistant to bacteriophages as well, through mutations in genes encoding for specific proteins. What would be a protein in the bacterial cell that, if mutated, would make that cell resistant to phage infection?arrow_forwardThe success of HAART (highly active antiretrovial therapy) against HIV is based on the idea that the probability of having an HIV virion that can simultaneously resist multiple anti-HIV drugs is very low. You were asked to investigate whether the same principle can be applied to another RNA virus, called Virus X. This is what you know about Virus X. (1) For a given antiviral drug, approximately 1 in 1,000 virions may carry a mutation that confers resistance against the said drug. (2) Roughly a total of 1010 virions can be found in an individual infected with Virus X. Assuming that all the drugs work independently of each other (i.e., mutations that allow resistance to one drug have no effect on the resistance to the other drugs), then minimally how many drugs are needed for this treatment regimen to work? Question 4 options: 1) 7 2) 6 3) 5 4) 4 5) 3arrow_forward
- The size of a DNA fragment that can be inserted into an unmodified λ vector is very limited. Large segment in the central region of the λ DNA molecule can be removed without affecting the ability of the phage to infect Escherichia coli cells. However, the deletion of this non- essential region does affect the life cycle of the bacteriophage. Explain this statement.arrow_forwardA" is a retrovirus. It can integrate DNA into random sites of human genome. Another virus "B" can integrate DNA at a specific site of human genome. Which one of these viruses would make a better vector for gene therapy? Briefly explain.arrow_forwardwhen various strains of lambda phage are seeded on a lawn of e.coli, they can form clear or turbid plaques. Explain the difference between the two types of plaques. can all bacteriophage form clear and turbid plaques?arrow_forward
- The dUTPase enzyme is used by the African swine fever virus to repair its own DNA, as the cells the virus infects in swine do not express the dUTPase protein. Which of the following is a reasonable explanation for the role of the dUTPase in the virus lifecycle? Explain your choice in 25 words or less. The dUTPase is necessary to remove dUTP from the viral genome, as uracil should not be present in DNA The dUTPase is necessary to remove dUTP from the viral genome, as uridine cannot correctly base pair with adenine-containing bases The dUTPase is necessary to remove dUTP from the viral genome, as uridine has the wrong sugar component for building DNA More than one of the above answers is correct None of the above answers is correctarrow_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_forwardE. coli cells are simultaneously infected with two strains of phage λ. One strain has a mutant host range, is temperature sensitive, and produces clear plaques (genotype h st c); another strain carries the wildtype alleles (genotype h+ st+ c+). Progeny phages are collected from the lysed cells and are plated on bacteria. The following numbers of different progeny phages are obtained: Progeny phage genotype Number of plaques h+ c+ st+ 321 h c st 338 h+ c st 26 h c+ st+ 30 h+ c st+ 106 h c+ st 110 h+ c+ st 5 h c st+ 6 a. Determine the order of the three genes on the phage chromosome. b. Determine the map distances between the genes. c. Determine the coefficient of coincidence and the interferencearrow_forward
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