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Viruses (Living Thing): Cells
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Viruses (Living Thing) also shows up in the Retriever categories:
Viruses (Malicious Software) , and more.
Viruses (Malicious Software) , and more.
Viruses are extremely small infectious agents that invade cells of all types. Once inside another cell, viruses become hijackers, using the cells' machinery to produce more viruses. Whether viruses constitute living organisms or merely conglomerations of molecules has been a source of debate for many years.
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Viruses are much smaller than other living things like bacteria. Viruses are not alive. They do not do all of the things that living things do. They can only make more copies of themselves when they are inside living cells.
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Viruses infect living cells and once inside, transform the cell essentially into a factory for making more viruses. These acellular particles are composed of nucleic acid (genetic material), proteins and, in some cases, lipids as well.
Bacteria are much bigger than viruses, and much more complex. A typical bacterium has a rigid cell wall containing a cell membrane, which holds the cytoplasm. Within this fluid are chromosomes (made up of DNA) that hold the instructions for making new bacteria and performing other functions. There may ... be loose bits of DNA called plasmids floating in the cytoplasm, and ribosomes, which are used for copying DNA so the cell can reproduce. Some bacteria have threadlike structures called flagella that they use to move around.
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The only defense you have against viruses is your immune system. Viruses have proteins on their surface by which they enter your cell. (Some animal viruses take along a portion of the cell membrane when they leave your cells, too.) Some of the viral proteins attach to protein receptors in your cell membranes. Viral proteins are recognized as foreign by your immune system. The immune system contains white blood cells called T and B cells which make and secrete antibodies (proteins) to fight foreign molecules (including allergens), cells, and viruses. These foreign molecules, etc., are referred to as antigens.
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The viruses that infect eukaryotic cells vary in size .... The poliovirus has 7,600 RNA nucleotides; the vaccinia (cowpox) virus has 240,000 DNA nucleotide pairs (7). To use computer terms again, the computer viruses that infect personal computers range in size from 1.9 kilobytes to 60 kilobytes. For comparison, a very simple personal computer (a yeast cell) has genetic instructions equivalent to about 8 megabytes. An advanced personal computer (a human cell) contains about 1.5 gigabytes of stored programs, counting the backup copy and the unused programs (silent DNA).
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