Retroviruses for Dummies

What is

• a virus? A virus is cause of infection, normally too small to see with ordinary microscopes. A virus is not a cell, like a bacterium, but a piece of RNA or DNA (its genome) wrapped up in a protein coat. It can only copy itself (replicate) by invading the cells of living creatures (hosts) and making them do the copying. 
• a retrovirus? A retrovirus is a special type of virus that is RNA based when it is a free virus, but once it enters a host cell, it produces a DNA version of its genome and inserts the DNA version into the DNA of the cell. The cell then "reads" the viral DNA resulting in the production of more retroviruses.
• an exogenous retrovirus? Exogenous means from outside the body. An exogenous retrovirus is a retrovirus that invades your cells from outside. 
• an endogenous retrovirus? Endogenous means from within the body. An endogenous virus is something you acquire by inheritance - your parents passed it down to you.
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