The characteristic that makes viruses different than bacteria is viruses need to eat almost constantly in order to remain alive. The only function viruses need to do is to reproduce and in order to do it, they need to eat constantly. In contrast to it, bacteria do not need to eat constantly in order to survive. Viruses are not a full fledged cell. The only structures they have is a protein coat wrapped up around their genetic material i.e. their DNA/RNA. The protein coat around their genetic material is known as capsid.
