Biology, Eighth Edition (Raven)

Chapter 27: Viruses

Entry of Virus into Host Cell

How are viruses able to enter cells? In order for a virus to infect a cell, it must bring its DNA or RNA into contact with the host cell. Therefore, infection requires that the virus get through the cellular membrane. Some viruses remain outside the cell. They attach to the membrane at specific receptor sites. Once attached the virus injects its DNA or RNA into the cell. Enveloped viruses are enclosed in a membrane similar to that of the host cell. The virus and the envelope fuse and the virus enters the cell through endocytosis. In the first example only the genetic material enters the cell. In the second case the entire virus with the exception of the envelope enters the cell.

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


1.	Viral spikes

		A)	attach non-specifically to host cell receptors
		B)	attach specifically to host cell receptors
		C)	are made of carbohydrate
		D)	are present in all viruses

2.	In viral entry by endocytosis

		A)	host plasma membrane surrounds whole virion and forms a vesicle
		B)	host plasma membrane surrounds only viral protein coat and forms a vesicle
		C)	host plasma membrane surrounds only viral nucleic acid and forms a vesicle
		D)	host spikes fuse with host plasma membrane

3.	After the virus nucleocapsid is released from the vesicle into the host cell cytoplasm

		A)	the viral nucleic acid is destroyed
		B)	it remains intact
		C)	the capsid protein is removed
		D)	the capsid protein becomes thicker

4.	A naked virus fuses with host cell membrane.

		A)	True
		B)	False

5.	Viruses with spikes usually enter host cells by endocytosis.

		A)	True
		B)	False