Answer b. Temperate phages (such as lambda phage) can reproduce using both the lytic and the lysogenic cycle. Their viral genome will integrate with host DNA and replicate along with it fairly harmlessly, or may even become established as a plasmid. Differentiate between lytic and lysogenic cycles. Its double-stranded DNA genome becomes incorporated in the host DNA. In the case of V. cholera, phage encoded toxin can cause severe diarrhea; in C. botulinum, the toxin can cause paralysis. Environmental stressors such as starvation or exposure to toxic chemicals may cause the prophage to be excised and enter the lytic cycle. Not only are these drugs untested or unregistered but they are also in short supply. In contrast, the lysogenic cycle does not result in immediate lysing of the host cell. HIV is an example of a virus that produces a chronic infection, often after a long period of latency. During the lytic cycle of viral replication, the virus hijacks the host cell, degrades the host chromosome, and makes more viral genomes. Structural proteins and phage genomes self-assemble into new phage particles. As the lysogenic cycle allows the host cell to continue to survive and reproduce, the virus is reproduced in all of the cell’s offspring. Is RNA-dependent RNA polymerase made from a viral gene or a host gene? This situation is an example of “compassionate use” outside the well-established system of regulation and governance of therapies. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. Figure 3. Virology, 479-480, 310â330. The second stage of infection is entry or penetration. A prime example of a phage with this type of life cycle is the lambda phage. The burst size is the maximum number of virions produced per bacterium. A patient may be unaware that he or she is carrying the virus unless a viral diagnostic test has been performed. Once a hospital realizes a patient like Duncan is infected with Ebola virus, the patient is immediately quarantined, and public health officials initiate a back trace to identify everyone with whom a patient like Duncan might have interacted during the period in which he was showing symptoms. On September 15, nine days before he showed up at the hospital in Dallas, Duncan had helped transport an Ebola-stricken neighbor to a hospital in Liberia. Answer d. A virus obtains its envelope during release. Bacteriophage lambda: Early pioneer and still relevant. However, one of the nurses charged with Duncan’s care did become infected. Examples of this are demonstrated by the poliovirus, which exhibits tropism for the tissues of the brain and spinal cord, or the influenza virus, which has a primary tropism for the respiratory tract. Which of the following leads to the destruction of the host cells? The timeline of the Duncan case is indicative of the life cycle of the Ebola virus. During dormancy, viruses do not cause any symptoms of disease and may be difficult to detect. must first be converted to a mRNA before it can be translated. If the viral genome is RNA, a different mechanism must be used. RecA (a cellular protein) detects DNA damage and becomes activated. Specialized transduction occurs at the end of the lysogenic cycle, when the prophage is excised and the bacteriophage enters the lytic cycle. Answer b. Lytic animal viruses follow similar infection stages to bacteriophages: attachment, penetration, biosynthesis, maturation, and release (see Figure 4). Bacteriophages, viruses that infect bacteria, may undergo a lytic or lysogenic cycle. Attachment is the first stage in the infection process in which the phage interacts with specific bacterial surface receptors (e.g., lipopolysaccharides and OmpC protein on host surfaces). With lytic phages, bacterial cells are broken open (lysed) and destroyed after immediate replication of the virion. If no viable host cells remain, the viral particles begin to degrade during the decline of the culture (see Figure 8). The lytic cycle leads to the destruction of the host cells. The majority of plant viruses are positive-strand ssRNA and can undergo latency, chronic, or lytic infection, as observed for animal viruses. Note that NusA can stimulate the activity of the Q protein. How does reverse transcriptase aid a retrovirus in establishing a chronic infection? Figure 7. Even the smallest and simplest of cells, prokaryotic bacteria, may be attacked by specific types of viruses. HIV, an enveloped, icosahedral retrovirus, attaches to a cell surface receptor of an immune cell and fuses with the cell membrane. A prime example of a phage with this type of life cycle is the lambda phage. Nine days passed between Duncan’s exposure to the virus infection and the appearance of his symptoms. March 18, 2005. Ebola virus is transmitted through direct contact with droplets of bodily fluids such as saliva, blood, and vomit. The chief difference that next appears in the viral growth curve compared to a bacterial growth curve occurs when virions are released from the lysed host cell at the same time. "WHO Ebola Data and Statistics." The integrated phage genome is called a prophage. Some viral infections can be chronic if the body is unable to eliminate the virus. As the lysogenic cycle allows the host cell to continue to survive and reproduce, the virus is reproduced in all of the cell’s offspring. "A Genetic Switch. The various mechanisms that HIV uses to avoid being cleared by the immune system are also used by other chronically infecting viruses, including the hepatitis C virus. At this point they initiate the reproductive cycle, resulting in lysis of the host cell. Protein cl turned ON, with repressor bound to OR2 polymerase binding is increased and turn OFF OR1. Since the phage is integrated into the host genome, the prophage can replicate as part of the host. What is the difference between a contagious pathogen and an infectious pathogen? Increased concentrations of repressor increase binding. Days later, Duncan returned to the eclipse phase, Duncan would have been unable to transmit the to. 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