The Structure of HIV

HIV, or human immunodeficiency virus, is the virus that precipitates AIDS. According to the Centers for Disease Control (CDC), HIV differs from other viruses in that it attacks the immune system by finding white blood cells and destroying them. The structure of the HIV particles, referred to as "virions," are also uniquely structured and bear little resemblance to other viruses.

Virus Class

• HIV is part of a special group of viruses called "retroviruses" which require a host cell in order to replicate. Retroviruses contain RNA as their hereditary material, instead of the significantly more common DNA. RNA, or ribonucleic acid, differs from DNA as it only has one chain of nucleotide units, while DNA has two. Nucleotide units are made of a ribose sugar, phosphate and a nitrogenous base.

Features

• An HIV viron's diameter is roughly 100 to 150 billionth of a meter. Each particle surrounds itself with a "viral envelope," which is comprised of a membrane made of lipid and plasma material. Polypeptide chains, which consist of linked amino acids, jut out and contain proteins that allow the particle to link itself to other cells. There are 72 of these chains on the surface of a virion. They look like little spikes. The "capsid," or viral core of an HIV particle, is made from a protein called "p24" and is bullet shaped. Inside the capsid there are three enzymes called integrase, protease and reverse transcriptase. These three elements are necessary for the particle to replicate inside the bloodstream.

Reproduction

• HIV virions can only reproduce inside human cells. They search within the bloodstream for white blood cells, called T-cells, which are made up of the protein CD4. Once they have located the T-cell, a polypeptide on the surface of the virion will attach itself to the protein by fusing itself to the cell. The virion will then release its contents inside the CD4 protein. At this point, reverse transcription occurs, where the RNA contained inside an HIV particle is converted into DNA so that the disease becomes compatible with human genetic material. This DNA then travels to the cell's nucleus. Here, it is separated into human DNA and the HIV enzyme, integrase. The successful integration of infected DNA and integrase is known as "provirus."

Transmission

• While the provirus can remain inactive for long stretches of time, when the host cell becomes active, it will confuse the HIV gene as a human gene. It will take its enzymes and convert them into messenger RNA, which will then leave the cell and infect others using its exact HIV genetic makeup as a blueprint. This process of exact replication allows the virus to spread quickly.

Considerations

• HIV has only nine genes. This is drastically less than most viruses that generally have around 500 genes. HIV leads to AIDS when HIV particles have destroyed enough T-cells so that the body cannot fight infection. Most patients die of illnesses that a healthy body could otherwise fight.