viruses

• viruses are not cells. they are nucleic acids surrounded by proteins. they are not alive
• viruses are smaller than bacteria
• viruses have no plasma membrane, no cytoplasm, no ribosomes
• all viruses invade and reproduce inside the cells of other organisms. these cells are known as host cells
• the protein coat of a virus is called a capsid
• viruses contain genetic material either DNA or RNA
• attachment proteins stick up from the edge of the capsid. these let the virus cling onto a suitable host cell
• viruses use host cells to replicate themselves
• viruses use their attachment proteins to bind to complementary receptor proteins on the surface of host cells
• different viruses have different attachment proteins and therefore require different receptor proteins on host cells. some viruses can only infect one type of cells, other can infect lots of different types of cell
• viruses don't undergo cell division because they're not alive
• viruses inject their DNA and RNA into the host cell - this hijacked cell then uses its own machinery to replicate the virus particles