Chapter%2019 - Viruses are very simple genetic systems Here...

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0.5 µm Viruses are very simple genetic systems. Here, T2 bacteriophages infects E. coli .
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RESULTS 1 2 3 Extracted sap from tobacco plant with tobacco mosaic disease Passed sap through a porcelain filter known to trap bacteria Rubbed filtered sap on healthy tobacco plants 4 Healthy plants became infected Viruses are also important because they cause disease in crops, animals, and people. Tobacco Mosaic Virus was the first virus to be identified.
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RNA Capsomere Capsomere of capsid DNA Glycoprotein 18 × 250 nm 70–90 nm (diameter) Glycoproteins 80–200 nm (diameter) 80 × 225 nm Membranous envelope RNA Capsid Head DNA Tail sheath Tail fiber 50 nm 50 nm 50 nm 20 nm (a) Tobacco mosaic virus (b) Adenoviruses (c) Influenza viruses (d) Bacteriophage T4 Viruses come in a variety of shapes and sizes
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DNA Capsomere Glycoprotein 70–90 nm (diameter) 50 nm (b) Adenoviruses Many viruses, like this adenovirus, have an icosahedral (20-sided) capsid .
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(a) Tobacco mosaic virus 20 nm 18 × 250 nm Capsomere of capsid RNA Other viruses have a filamentous capsid, like TMV. These two common structures (helices and icosahedrons) are among the very few ways that non-symmetrical particles like proteins can join together to inclose a space.
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Head DNA Tail sheath Tail fiber 80 × 225 nm 50 nm (d) Bacteriophage T4 Complex viruses, like the T- even bacteriophages have capsid components made of both helical and icosahedral parts.
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Membranous envelope RNA Capsid Glycoproteins 80–200 nm (diameter) 50 nm
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