Some viruses can even be engineered to reproduce in cancer cells and trigger the immune system to kill those harmful cells. Because some viruses incorporate their DNA into host DNA, they can be genetically modified to carry genes that would benefit the host. Viruses are particularly vital to gene therapy. Some of these drugs stop DNA synthesis, preventing the virus from replicatingĪlthough viruses can have devastating health consequences, they also have important technological applications. Most antiviral drugs work by interfering with viral replication. Viral infections are best prevented by vaccines, though antiviral drugs can treat some viral infections. Unlike bacterial infections, antibiotics are ineffective at treating viral infections. This leads to a more chronic infection that is difficult or impossible to cure often only the symptoms can be treated. However, some viruses are not successfully treated by the immune system, such as human immunodeficiency virus, or HIV. Typically, viruses cause an immune response in the host, and this kills the virus. For example, the flu is caused by the influenza virus. In humans, viruses can cause many diseases. Each time the host’s cells go through replication, the virus’s DNA gets replicated as well, spreading its genetic information throughout the host without having to lyse the infected cells. From there, the viral DNA gets incorporated into the host’s DNA and the host’s cells. Like the lytic cycle, in the lysogenic cycle the virus attaches to the host cell and injects its DNA. These viruses break, or lyse, the cell and spread to other cells to continue the cycle. Using the host’s cellular metabolism, the viral DNA begins to replicate and form proteins. In the lytic cycle, the virus attaches to the host cell and injects its DNA. Some viruses reproduce using both methods, while others only use the lytic cycle. There are two processes used by viruses to replicate: the lytic cycle and lysogenic cycle. No matter the shape, all viruses consist of genetic material ( DNA or RNA) and have an outer protein shell, known as a capsid. However, bacteriophages (viruses that infect bacteria) have a unique shape, with a geometric head and filamentous tail fibers. Viruses generally come in two forms: rods or spheres. Viruses are so small that they are best viewed using an electron microscope, which is how they were first visualized in the 1940s. coli bacteria has a diameter of around 1 micrometer. Most viruses are only 20–400 nanometers in diameter, whereas human egg cells, for example, are about 120 micrometers in diameter, and the E. Not only are viruses microscopic, they are smaller than many other microbes, such as bacteria. A virus that is outside of a host cell is known as a virion. As such, there is some debate as to whether or not viruses should be considered living organisms. They may use an animal, plant, or bacteria host to survive and reproduce. Viruses are tiny infectious agents that rely on living cells to multiply.
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