Vocabulary

vector protease inhibitor oncogene proto-oncogene emerging disease inactivated virus attenuated virus viroid prion

figure 24-5

The painful shingles rash, caused by a herpes virus, is limited to an area of the skin innervated by a particular nerve branch, for example, on the side of the chest.

figure 24-5

The painful shingles rash, caused by a herpes virus, is limited to an area of the skin innervated by a particular nerve branch, for example, on the side of the chest.

Glycoprotein

Lipid bilayer membrane

(envelope)

Matrix protein

Capsid

RNA genome

Reverse transcriptase

figure 24-6

Human immunodeficiency virus (HIV) contains two identical RNA molecules and two molecules of reverse transcriptase, which makes double-stranded DNA from the RNA.

figure 24-6

Human immunodeficiency virus (HIV) contains two identical RNA molecules and two molecules of reverse transcriptase, which makes double-stranded DNA from the RNA.

Acquired Immune Deficiency Syndrome (AIDS)

The human immunodeficiency virus (HIV) causes AIDS. HIV gradually destroys an infected person's immune system. HIV is spread by sexual contact; by contact with infected body fluids, such as blood, semen, or vaginal fluids; and from mother to fetus. Glycoproteins on the surface of HIV, shown in Figure 24-6, bind to specific receptor proteins found on macrophages, which are immune system cells.

Figure 24-7 summarizes how HIV infects macrophages. First, the virus attaches to the CD4 and CCR5 receptors on the cell surface. To enter the cell, the HIV glycoprotein must bind to both CD4 and the CCR5 coreceptor. Then, the viral envelope fuses with the cell membrane and releases the capsid into the host cell. The enclosed capsid enters the cell cytoplasm, where viral RNA and the enzyme reverse transcriptase are released. Reverse transcriptase uses the viral RNA as a template for making a double-stranded DNA version of the viral genome. The HIV DNA enters the cell's nucleus and inserts itself into the DNA of the host's chromosome, becoming a provirus. Cellular enzymes transcribe and then translate the HIV genes into viral proteins. Then, some of the HIV particles assemble. Finally, the cell membrane pinches off and forms a viral envelope as the newly made HIV particles separate from the cell. Viral replication of HIV results in many mutations. Eventually, the virus recognizes other coreceptors, such as those found on helper T cells. In helper T cells, the HIV particles are released by lysis.

figure 24-7

The human immunodeficiency virus (HIV) infects certain cells of the immune system. In step O, HIV attaches to receptors on the cell surface. In step ©, the capsid is released into the host cell. In steps Q and O, the viral RNA is copied into double-stranded DNA. As shown in step Q, the viral DNA inserts into the host cell's DNA. In step Q, viral proteins are made. Then, in step O, HIV particles assemble. In step Q, newly made HIV particles pinch off from the cell membrane. In some immune cells, HIV particles are released by lysis, shown in step Q.

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