Illustration of the replication cycle of the human immunodeficiency virus (HIV). From left, the glycoprotein spikes on the viral envelope attach to surface proteins on a CD4+ T-lymphocyte white blood cell. The RNA (ribonucleic acid) genome (red) and reverse transcriptase enzyme (yellow spheres) are injected into the cell. Reverse transcriptase transcribes the single-stranded RNA to double stranded DNA (deoxyribonucleic acid), which can then integrate into the host cell's DNA (blue helix). The virus hijacks the cell's nuclear machinery, causing it to produce viral RNA molecules and proteins. The proteins assemble around the RNA forming the viral cores, which then bud from the cell, taking part of the membrane as an envelope.