12.10.1 HIV: An Attack on the Immune System

Question 1

HIV: An Attack on the Immune System

Answer 1

• AIDS (acquired immunodeficiency syndrome) is caused by the retrovirus HIV (human immunodeficiency virus).
• HIV injects RNA into a host cell and uses reverse transcriptase to synthesize DNA, which will then be incorporated into the cell’s genome. The DNA will direct the synthesis of new viral RNA, which will direct then the synthesis of viral proteins. These proteins and the mRNA will assemble and form new viruses.
• HIV requires the presence of specific receptors on the surface of cells to infect the cells. These receptors are found on T cells, macrophages, and some B cells

Question 2

HIV

Answer 2

• The reproductive cycle of HIV begins when the virus attaches and fuses with the plasma membrane of a cell. HIV entry into the cell requires CD4, a molecule on the surface of helper T cells, and some macrophages and B cells. Other coreceptors for the HIV virus include fusin and CCR5.
• Once the virus enters the cell, the viral protein
  reverse transcriptase begins synthesizing DNA from the
  viral RNA strand, which eventually gives rise to a segment of double stranded DNA.

Question 3

note

Answer 3

• The double stranded viral DNA then enters the nucleus and inserts into the host cell’s genome. The DNA then directs the synthesis of mRNA that encodes viral proteins.
• The mRNA exits the nucleus and enters the cytoplasm, where it will direct the synthesis of viral proteins.
• The viral proteins will then assemble with the mRNA and bud off of the host cell as new virus particles.
• The chart to the left shows the timeline of an HIV infection. In the first year of an HIV infection, the virus concentration in the blood peaks sharply and then rapidly declines due to an immune response. Notice that at the same time, the concentration of T cells and HIV antibodies in the blood has increased.
• During the period when virus concentration is low, the virus continues to replicate itself in the lymphatic system. As the lymphatic system breaks down, the virus concentration increases in the blood. At the same time, the T cell concentration in the blood decreases as T cells are depleted.
• During the final stages of an HIV infection (AIDS), the T
  cell concentration reaches an all time low while the virus
  continues to replicate.

Question 4

What is the role of reverse transcriptase in a retrovirus?

Answer 4

• Reverse transcriptase is used to catalyze the synthesis of DNA from RNA.

Question 5

True or false?

Antibody concentrations decrease throughout an HIV infection.

Answer 5

• false

Question 6

True or false?
The cause of death in people with AIDS is not the virus itself but the inability of the immune system to fight off infection.

Answer 6

• true

Question 7

Which immune cells are most susceptible to HIV infection?

Answer 7

• helper T cells

Question 8

A mutation in what type of protein makes people resistant to HIV?

Answer 8

• Chemokine receptor

Question 9

In 1981, health officials noticed an increase in _________________, a rare form of cancer, which was the first indication of a new epidemic.

Answer 9

• Kaposi’s sarcoma

Question 10

HIV is a/an _________ virus.

Answer 10

• RNA

Question 11

True or false?

During an HIV infection, as anti-HIV antibodies rise in the body, the number of virus particles in the blood goes down.

Answer 11

• true