In: Biology
Compare and contrast the structure, life cycle, and host cell type of naked and enveloped viruses.
Some viruses, called envelope viruses, are encased in an envelope derived from the host cell. Viral envelopes normally contain viral glycoproteins. Those that do not contain an envelope are called naked viruses.
Some enveloped viruses directly fuse with the plasma membrane followed by uncoating. In these cases the activity of a fusion protein is not dependent on pH change, but rather is induced in response to receptor binding. Most naked viruses enter by receptor-mediated endocytosis whereby the host cell cytoplasmic membrane invaginates and pinches off, placing the virus in an endocytic vesicle. Naked viruses may cross the plasma membrane directly or may be taken up by endosomes. They then cross (or destroy) the endosomal membrane followed by uncoating.
Envelope viruses are those responsible for HIV, herpes, smallpox, influenza and rabies. Naked viruses are responsible for warts, polio, and Hepatitis A. Enveloped viruses acquire a membrane after the internal components have been assembled, whether they are helical or icosahedral nucleocapsids. Host cell receptors play a crucial role for the entry of naked virus. Entry of enveloped virus is mediated by membrane fusion.