Virus: a microscopic infective agents which consist of DNA or RNA surrounded by a protein, lipid, or glycoprotein shield. Viruses, unlike other prokaryotic or eukaryotic cells, cannot function on their own, and must infect a host cell in order to survive. They will invade normal cells,insert their own viral genetic material, and take over the host cell's functions. Now, when the host cell reproduces, it produces more cells that have the viral genetic material, allowing the virus to spread quickly.
Viruses are really quite simple; their primary function is to effectively infect a host cell and pass on their genetic material. To do this, they have a few simple anatomical structures. Although not all viruses are identical, they all have some important pieces. (see left diagram)
The proteins that compose a VIRION (all parts of the virus) are called STRUCTURAL PROTEINS. The protein coat of the virus inside the MATRIX that surrounds the single strand RNA or the double helix DNA is called the CAPSID. Some viruses have a protective outer membrane called the ENVELOPE, or the LIPID MEMBRANE. This membrane may have various GLYCOPROTEINS which aid the virus in attaching to a host. There are different kinds of viruses, some more complex than others. A standard virus contains the double-strand genetic material DNA. However, a retrovirus, like HIV or the common cold, contains single-strand RNA which is then fused into DNA. This involves an additional step in reshaping the RNA into DNA, which does not always replicate perfectly. This means that more errors in the genetic code are made, therefore resulting in more mutations. (making retroviruses more difficult to treat) |