UA BSC 114 - CH. 19 Notes- BSC 114 (5 pages)

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CH. 19 Notes- BSC 114



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CH. 19 Notes- BSC 114

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Pages:
5
School:
University of Alabama
Course:
Bsc 114 - Principles of Biology I

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Ch 19 Viruses Viruses o A virus is an infectious particle consisting of genes packaged in a protein coat o Viruses are much simpler in structure than even prokaryotic cells o Viruses cannot reproduce or carry out metabolism outside of a host cell Structure of Viruses o Viruses are not cells o A virus is a very small infectious particle consisting of nucleic acid either DNA or RNA enclosed in a protein coat and in some cases a membranous envelope Viral Genomes o Viral genomes may consist of either Double or single stranded DNA or Double or single stranded RNA o Depending on its type of nucleic acid a virus is called a DNA virus or an RNA virus o The genome is either a single linear or circular molecule of the nucleic acid o Viruses have between three and several thousand genes in their genome Capsids and Envelopes o A capsid is the protein shell that encloses the viral genome o Capsids are built from protein subunits called capsomeres A capsid can have a variety of structures o Some viruses have accessory structures that help them infect hosts o Viral envelopes derived from membranes of host cells surround the capsids of influenza viruses and many other viruses found in animals o Viral envelopes contain a combination of viral and host cell molecules o Bacteriophages also called phages are viruses that infect bacteria o They have the most complex capsids found among viruses o Phages have an elongated capsid head that encloses their DNA o A protein tail piece attaches the phage to the host and injects the phage DNA inside The Lytic Cycle o The lytic cycle is a phage replicative cycle that culminates in the death of the host cell o The lytic cycle produces new phages and lyses breaks open the host s cell wall releasing the progeny viruses o A phage that reproduces only by the lytic cycle is called a virulent phage Bacteria have defenses against phages including restriction enzymes that recognize and cut up certain phage DNA An environmental signal can trigger the virus



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