Viruses are, by far, the smallest organisms in the world. Viruses are stripped down to an absolutely minimal design: a protein capsule containing DNA or RNA . A number of viruses contain their genetic information in RNA instead of DNA). Viruses survive and reproduce by infecting a cell and commandeering the cellular synthetic machinery to make more viruses. Then the viruses lyse the cell and start the cycle over again.
There is an entire class of viruses known as bacteriophages that prey exclusively on bacteria. Many of these viruses have a common structure.
The DNA is injected into the bacteria through the baseplate.
HIV, the virus that causes the disease AIDS and is the most famous virus in the world right now, has this basic structure:
This is an image of rhinovirus 14, one of the many rhinoviruses.
What you are seeing are the interlocking proteins of the virus capsid. Each
color represents a different type of protein.
This image was developed at the University of Wisconsin. This and many other virus structures are available: Follow this link to view an example virus structure.