3D computer model of the Human Immunodeficiency Virus, HIV-1. The virus particle, or virion, rotates and then appears as a cutaway illustration showing the internal viral structure.
The golden spikes (or knobs) are the trimeric envelope proteins that help the virus to attach to target cells. They are composed of gp120 (outer knob) and gp41 (stalk, trans-membrane section, and cytoplasmic tail). Next comes the viral envelope (translucent green) derived from the host cell plasma membrane during budding of the virus particle. Immediately beneath the viral envelope envelope lie the matrix proteins (MA: blue cage-like structure). Lying across the internal space is the purple capsid (or core). This bullet-shaped structure contains the viral genome (in the case of HIV this is two strands of RNA) and the enzyme reverse transcriptase.