CLAUS LUNAU / SCIENCE PHOTO LIBRARY CLAUS LUNAU / SCIENCE PHOTO LIBRARY
Virus life cycle, illustration. Viruses consist of a genome and sometimes a few enzymes stored in a capsule (called a capsid) made of protein, and sometimes covered with a lipid layer (an 'envelope'). Viruses cannot reproduce on their own, and instead propagate by subjugating a host cell (red) to produce copies of themselves. They sabotage the host cell in the process and produce their next generation. The cycle shown here starts at upper right, with the virus attaching and releasing its genetic material into the cell. The cellular mechanisms are hijacked and used to create new viruses, which are released from the cell at lower right, usually killing the cell in the process.
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