It is difficult to treat a viral infection of either type because the virus becomes so well integrated with the host genome that inhibiting the virus also inhibits the host cells. In bacterial infections, on the other hand, one can generally kill prokaryotic bacteria with little effect on the eukaryotic host cells. Generally an electron microscope is required to see an actual viral particle, so the approximate size range is 17 to 1000 nanometers. A bacteriophage is a virus that infects a bacterium. The tail retracts, and the tube within it penetrates the bacterial cell wall, permitting the T4 nucleic acid to enter the bacterium.
Viruses recognize the specific cell surface markers of the cells they infect.
This animal virus penetrates the host cell via endocytosis. Although the coat is shed, the protein RNA and the enzyme reverse transcriptase stay in the cytoplasm. A plant virus infects its host by entering at a point of injury, bacterial viruses inject their nucleic acid into the bacterium through the cell wall. Most species of bacteria are identified by their metabolic actions, which are determined by how they respond when grown on different growth media. The bacterial cell wall is a network of polysaccharide molecules cross-linked by polypeptides.