They consist of a nucleic acid core surrounded by a protein coat called a capsid . There is more genetic similarity between a virus and its host than among viruses.
Viruses are quite small.
Phages are viruses that attack bacteria. The virus attaches to receptors on the host cell wall. The nucleic acid of the virus moves through the plasma membrane and into the cytoplasm of the host cell. The capsid of a bacteriophage remains on the outside. In contrast, many viruses that infect animal cells enter the host cell.