Microbiology - Viruses are obligated to reproduce within...

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Viruses are obligated to reproduce within cells ( obligate intracellular parasites ) - To reproduce, they commandeer the cellular machinery of the host they infect and use it to manufacture copies of themselves. - Relies on host machinery whenever possible. Viral genomes consist of either DNA or RNA, single or double stranded, and linear or circular. Note: if the ratio of adenine and thymine in a DNA virus is not one to one, the genome of the virus must be single-stranded. Size is a limiting factor that influences all viral genomes. - The exterior protein shell of a virus (the capsid ) is typically a rigid structure of fixed size that cannot expand to accommodate a larger genome. To adapt to this size constraint, viruses have depended on host-encoded proteins for transcription, translation and replication - They mooch off of the cells they infect. - Viral proteins and host proteins are translated by the same ribosome. - Can encode more than one protein in a given length of genome. - Genes can overlap reading frames can vary . Tail fibers – attach to the surface of the cell Head – where the DNA of the virus is located. The entire viral capsid is composed of protein, while the viral genome is composed of nucleic acid. - Sometimes there is an envelope that surrounds the capsid. - The proteins in the envelope are sometimes encoded by the virus’s own genome. - The surface of a virus determines what host cell it can infect . - The virus binds to a specific receptor on the cell surface as the first step in infection. - Explains why specific cell types are susceptible to infection. - The viral surface is also important for recognition by our immune system. Viruses acquire envelopes by budding through the host membranes If antibodies to a viral capsid protein are ineffective in blocking infection, this might indicate that the virus is enveloped, so the antibody will not recognize capsid protein in an infectious virus. Viruses attach to their host cells, and then their viral genome penetrates through the cell membrane. Next step: lytic or lysogenic cycle Lytic cycle - Once the genome has entered the host cell, the host’s polymerases begin to rapidly transcribe and translate it. - It makes hydrolase , which degrades the entire host genome (it’s an early gene , meaning that this group of genes is expressed immediately after infection).
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- New capsids assembles itself around a new genome - Lysozyme is then produced, which is a late gene . This destroys the cell wall. - The cell then lyses because the osmotic pressure is no longer counteracted. - Disadvantage : after the viruses reproduce, the host cells are destroyed. This is an evolutionary disadvantage for the viruses. A single virus contains a single genome and contains a specific type of progeny
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Microbiology - Viruses are obligated to reproduce within...

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