Flexi Says: Viruses vary in their structure. They can be cylindrical, icosahedral, complex, or enveloped. A virus particle consists of DNA or RNA within a protective protein coat called a capsid. The shape of the capsid may vary from one type of virus to another. The capsid is made from the proteins that are encoded by viral genes within their genome. The shape of the capsid serves as one basis for the classification of viruses. The capsid of the virus can be icosahedral. Virally coded proteins will self-assemble to form a capsid. Some viruses have an envelope of phospholipids and proteins. The envelope is made from portions of the host’s cell membrane. It surrounds the capsid and helps protect the virus from the host’s immune system. The envelope may also have receptor molecules that can bind with host cells. They make it easier for the virus to infect the cells.
