Biology, Eighth Edition (Raven)

Chapter 27: Viruses

Mechanism for Releasing Enveloped Viruses

What is an advantage of having an envelope for a virus? Many viruses that attack animal or plant cells have an envelope of glycoproteins surrounding the body of the virus. The envelope is derived from the cellular membrane of the host cell in most cases. The envelope binds to receptors on the host cellular membrane and the virus can enter the cell by endocytosis. Unlike the T phages and other viruses without envelopes the capsid enters the cell along with the genetic material. After new copies of the virus are synthesized by the host cell, the viruses can exit the cell. As they pass through the cellular membrane each new virus picks up an envelope. The reproductive cycle of a virus with an envelope is not necessarily fatal to the host cell unlike the lytic cycle of phages. Examples of animal viruses with envelopes include viruses causing the following diseases: herpes, chicken pox, mononucleosis, west nile, hepatitis C, influenza, measles, mumps, rabies, and HIV.

View the animation below, then complete the quiz to test your knowledge of the concept.


1.	The first event to occur is

		A)	inside of the host cell membrane becomes coated with viral matrix protein
		B)	viral capsid becomes enclosed by cell membrane
		C)	inside of host cell membrane becomes coated with capsid
		D)	viral spike proteins are inserted into host cell membrane

2.	The viral capsid

		A)	engulfs the viral spikes
		B)	surrounds the viral matrix protein
		C)	becomes completely enclosed by the region of the cell membrane into which the spikes and matrix protein are embedded
		D)	is dissolved

3.	Enveloped viruses are usually released from the host cell by

		A)	budding
		B)	lysis of the host cell
		C)	endocytosis
		D)	phagocytosis

4.	A portion of the viral envelope comes from the cell membrane of the host cell.

		A)	True
		B)	False

5.	Enveloped viruses are usually released from the host cell by exocytosis.

		A)	True
		B)	False