Why do cells allow in viruses? Do viruses have protein "keys" similar to those of necessary functions in our body?
How many cells does a virus need to kill for us to feel it?
Would a virus be considered a cell?
Cells do not 'allow' viruses into them but the two membranes, one from the cell and the viral envelope, are both comprised of fat (lipid) molecules that fuse together. Viral proteins have evolved to recognize and bind to cell proteins but the purpose of the cell protein is not to bind to the viral protein but to do something else in the body.
sometimes viruses do not actually kill a cell. I know that this is the way all of the sites I have sent you to state how viruses kill cells. But the truth is a little more complicated than that. The cell itself can detect a viral infection and can kill itself committing cellular suicide. Our own immune system responds and kills even more cells. How many cells need to die before we have symptoms? No one knows.
No viruses are not cells. Cells are very complicated with numerous intracellular organelles that harvest energy, make proteins, etc. Viruses have none of these organelles.