Chapter 24 Viruses – Flashcards
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Viruses are considered nonliving because
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1. they cannot reproduce by themselves 2. they are not made of cells 3. they cannot carry out metabolism by themselves
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The study of viruses is a part of biology because
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they are active inside living cells
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Biologists now know that viruses
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contain RNA or DNA in a protein or lipid-protein coat
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The capsid of a virus is the
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protective outer coat
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Viruses are classified according to
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1. whether they contain RNA or DNA 2. the shape of their genome 3. whether they have a membrane envelope
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Viruses do not have
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cytoplasm, ribosomes, or mitochondria
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Tobacco mosaic virus
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1. can crystallize 2. causes disease in tobacco plants 3. is smaller than bacterium
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Scientists first began to study viruses because they
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could not be seen but caused disease
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Viruses that use reverse transcriptase to cause their host cells to transcribe DNA from an RNA templace are called
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retroviruses
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What contains only RNA?
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a viroid
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Unlike viruses, prions
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are composed only of protein
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A typical virus consists of
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a protein coat and a nucleic acid core
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How do viruses reproduce?
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Only in living cells
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Animal viruses often infect only specific host cells because
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the host cell must have specific receptors for proteins on the virus surface
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Antibiotics are ineffective against viral infections because
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antibiotics interfere with cellular processes that viruses do not perform
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What are hepatitis, SARS, and shingles?
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Viral diseases of humans
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What viruses are linked to cancer?
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hepatitis B virus, human papillomavirus, and Epstein-Barr virus
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What human activity is most associated with emergence of viruses not previously seen in humans?
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clearing of forest for housing
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Most scientists think that early viruses originated from
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existing cell parts
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HIV causes AIDS by
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gradually destroying a person's immune system
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What is a vector of viral diseases?
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mosquitoes, ticks, and humans
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What is the most successful at fighting viral diseases?
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vaccination and vector control
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Most scientists believe that viruses first appeared on Earth __ living cells appeared.
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after
