Can someone example to me why?
1. proteins in the viral capsid or on the surface membrane function to
bind the virus to the surface of a host cell
2. bacterium is not caused by aids.
3.viral diseases can be prevented with vaccines but not treated with antibiotics.

1. It does this to protect host's cells and keep the virus in the same spot so white blood cells can kill them. 
2. Aids are not caused by bacteria because what causes it is a sexual disease.
3. A vaccine is the disease but a weakened form so then the white blood cells can learn how to kill the disease but antibiotics can only slow down the disease so that the white blood cells can kill it. 
I hope this helps you.