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HIV Life Cycle

Uploaded by ihatesuchin on Jul 05, 2004

A HIV particle approaches and attaches to a lymphocyte. (Lymphocytes, which include helper T cells and killer T cells, are small white blood cells that are critical in immune defense and are HIV's principal target.)

In order to replicate itself, an HIV particle must get its RNA, which is the genetic blueprint for a new particle, inside the host cell. To do that, the viral particle must first bind to two chief receptors on the outside of the host cell, much like a key fitting into a lock. If even one of those receptors, which are known as CD4 and CCR5 receptors, is missing, the viral core containing the RNA will not get into the cell. (Researchers have found that some AIDS patients, known as long-term non-progressors because they are HIV-positive yet show few or no symptoms of the disease, are missing the gene for one of these receptors.) The binding process is facilitated by a molecule on the surface of the HIV particle called gp120 (for glycoprotein with a molecular weight of 120). Once the viral particle has successfully binded to the host cell, its core can pass through the cell wall into the cell's cytoplasm. The core then dissolves, leaving the RNA and catalyzing enzymes ready to begin the process of replication.

Viral RNA transforms itself into double-stranded DNA, and then integrats into the host cell's DNA in order to produce new viral RNA.

Once inside the host cell, the viral RNA migrates toward the nucleus through the cell's cytoplasm and eventually through the nuclear membrane. A series of steps that ultimately ends in a new HIV particle follows. First, through a process known as reverse transcription, the enzyme known as reverse transcriptase catalyzes the formation of double-stranded viral DNA using the single-stranded viral RNA as a template. Employing other enzymes such as integrase (shown by the starburst in step 4 and in the graphic at right above), the new viral DNA then breaks open the host cell's DNA and integrates itself into it. This leads to the formation of a new viral RNA strand, which migrates out of the host's DNA. The new viral RNA moves into the cytoplasm, where new viral proteins are built using the viral RNA as a blueprint.

A new viral particle is assembled and then migrates out of the host cell to infect new cells.

Once the viral protein parts have been built, they are assembled into...

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Uploaded by:   ihatesuchin

Date:   07/05/2004

Category:   Biology

Length:   2 pages (514 words)

Views:   8797

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