KEY TAKEAWAYS •
Viruses are not technically forms of life because they lack the recognized features that identify life forms.
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Viruses are obligate parasites and cannot replicate without a host cell.
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Viruses have been studied and treated for thousands of years with the most information gotten in the last hundred years about these particles.
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Viruses have three distinct shapes in general but there are some variations in certain types.
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There are different theories of virus evolution, particularly as they relate to the origin of viruses themselves.
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The viruses have several different classifications based on the type of nucleic acid inside the cell.
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The viral life cycle proceeds the same for most infections but some will have a less typical lysogenic cycle that doesn’t immediately kill the cell.
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Bacteriophage infections indirectly affect animals and humans because some will cause the bacteria infected to be much more virulent in general.
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