Biology, Eighth Edition (Raven)

Chapter 23: Systematics and the Phylogenetic Revolution

How the HIV Infection Cycle Works

What factors influence the time period from initial HIV infection and the development of symptoms? HIV is an unusual viral disease in that individuals can carry the virus for very extended periods of time without becoming ill, or exhibiting any symptoms at all. However, at any time, the symptoms of AIDS can manifest themselves. The variation in time until onset of the disease is associated with several factors. The most important is having a well-functioning immune system. Individuals with weak immune systems, such as older people or people with certain types of pre-existing infections develop AIDS more rapidly, on average, than other people do. Other factors that influence the onset of disease are treatment with various medications, the strain of HIV involved, and the genotype of the infected person.

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


1.	The HIV protein that is involved in attachment of the virus to host cells is

		A)	reverse transcriptase.
		B)	gp120.
		C)	CD4.
		D)	CCR-5.
		E)	CXCR-4.

2.	The HIV enzyme that makes a double-stranded DNA copy of the viral genome is

		A)	DNA polymerase.
		B)	RNA polymerase.
		C)	reverse transcriptase.
		D)	endonuclease.
		E)	gyrase.

3.	The type of cells infected by HIV are ________ early in the course of an infection and ________ late in the infection.

		A)	helper T cells ; cytotoxic T cells
		B)	helper T cells ; macrophages
		C)	macrophages ; cytotoxic T cells
		D)	macrophages ; helper T cells
		E)	macrophages ; helper B cells

4.	Attachment of HIV to a host cell requires a receptor and co-receptor on the surface of the host cell.

		A)	True
		B)	False

5.	HIV leaves an infected cell by breaking down its cell membrane.

		A)	True
		B)	False