In this computer generated image, the large object is a human CD4+ white blood cell, and the spots on its surface and the spiky blue objects in the foreground represent HIV particles.
Outside of a human cell, HIV exists as roughly spherical particles (sometimes called virions). The surface of each particle is studded with lots of little spikes. An HIV particle is around 100-150 billionths of a metre in diameter. That's about the same as:
0.1 microns
4 millionths of an inch
one twentieth of the length of an E. coli bacterium
one seventieth of the diameter of a human CD4+ white blood cell.
Unlike most bacteria, HIV particles are much too small to be seen through an ordinary microscope. However they can be seen clearly with an electron microscope. HIV particles surround themselves with a coat of fatty material known as the viral envelope (or membrane). Projecting from this are around 72 little spikes, which are formed from the proteins. Just below the viral envelope is a layer called the matrix, which is made from the protein p17.
The proteins make up the spikes that project from HIV particles. The viral core (or capsid) is usually bullet-shaped and is made from the protein p24. Inside the core are three enzymes required for HIV replication called reverse transcriptase, integrase and protease. Also held within the core is HIV's genetic material, which consists of two identical strands of RNA.
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