Prokaryotic cells and viruses

• cytoplasm


  has no membrane-bound organelles (unlike a eukaryotic cell). It has ribosomes but they are smaller than those in a eukaryotic cell.
• Plasma membrane


  Mainly made of lipids and proteins. Controls movement of substances in and out of the cell.
• Cell wall


  Supports the cell and prevents it from changing shape. Its made from a polymer called murein - a glycoprotein.
• Capsule


  Made up of secreted slime. Helps to protect bacteria from attack by cells of the immune system.
• Plasmids


  Small loops of DNA that aren't part of the main circular DNA molecule. They contain genes for things like antibiotic resistance, and can be passed between prokaryotes. They are not always present in prokaryotic cells and some can have several.
• No nucleus


  Instead, DNA floats free in the cytoplasm. It is circular DNA, present as one long coiled up strand. It is not attached to any histone proteins.
• Flagellum


  A long, hair like structure that grows out of a cell and enables the cell to move. Not all prokaryotes have one and some have more than one.
• Viruses


  tiny particles, smaller than bacteria and other pathogens, which must invade living cells in order to reproduce; when they invade, the cells are damaged or destroyed in the process releasing new particles to infect other cells