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14 Cards in this Set
- Front
- Back
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History |
Russian botanist ivanovsky - first to give clear cut evidence of virus Mayer- mosaic disease Schlesinger first to determine composition of a virus. |
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Nature of virus |
Size No independent metabolism Simple structure Absence of cellular structure Nucleic acids Crystallization No growth and division |
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Size |
Invisible in light microscope . Some are only 200A in diameter. Smaller than bacteria |
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No independent metabolism |
Cannot multiply outside a living cell . No independent metabolism,metabolically inactive outside the host cell as they do not posses enzyme systems and protein synthesis machinery. Thus they are endoparasites. Considered to be non living. |
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Complex |
Naked : vaccinia virus Capsid to which other structures are attached : some bacteriophage |
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Simple structure |
Nucleic acid core surrounded by protein coat. Differ from typical cells made up of proteins,carbs,lipids etc. they are just larger nucleoproteins. Myxovirus - membranous envelope made up of protein,lipids and carbohydrates outside the usual coat (derived from host cell) |
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Absence of cellular structure |
Cytoplasm absent hence no cytoplasmic organelles. No cell membrane . Utilize ribosomes of host cell for protein synthesis during reproduction. |
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Nucleic acids |
Either DNA or RNA Rous Sarcoma Virus(RSV) - cancer causing virus has both RNA,DNA. Called RNA-DNA Virus. |
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Crystallization |
Many small viruses crystalize and behave like chemicals |
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No growth and division |
Fully formed virus does not increase in size. Only its genetic material are capable of reproduction (host cell). They however posses two fundamental characteristics of living systems 1.nucleic acids as their genetic material. 2.they can reproduce (only inside host cell) |
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Structure of virus |
Virion- intact virus unit Nucleic acid core surrounded by protein coat to form nucleocapsid. Nucleocapsid - naked or surrounded by loose membrane Composed of subunits - capsomeres Capsid protects nucleic core from nucleases. |
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Three main shapes |
Spherical - polyhedral Helical - cylindrical or rod like Complex Can be naked or covered by envelope |
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Polyhedral |
Naked capsid: poliovirus, papilloma virus, adenovirus Enveloped : herpes simplex virus |
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Helical |
Naked : bacteriophage M13, tobacco mosaic virus Enveloped : influenza virus |
