HIV DNA. Molecular model of a sequence of DNA (deoxyribonucleic acid) produced by HIV (the human immunodeficiency virus) after infecting a human cell. This is a stage in the process where HIV replicates using human cell machinery, causing AIDS (acquired immune deficiency syndrome). DNA is a helical molecule (here spiralling across the image) made up of two interlocking sugar-phosphate strands bound together by their nucleotide bases. Three 'twists' of the helix are seen here. This is HIV-1, the more common of the two forms of HIV. This tubular model, overlaid on a space-filled model, shows 527 atoms. The atoms (tubular then space-filled colours) are: carbon (green, light blue), oxygen (orange, red), phosphorus (both pink), nitrogen (both blue). Hydrogen atoms not shown.