Influenza virus structure, cutaway artwork. The core of the virus is its genetic material, here 8 coloured ribbons of single-stranded RNA (ribonucleic acid). Surrounding these is a geometrical protein coat, the capsid (purple). Surrounding this is the spherical shape of the external membrane, consisting of lipids (green and yellow). Embedded in the membrane are three types of surface protein: haemagglutinin (H, red), neuramidase (N, orange), and the M2 ion channels (blue). The ion channels (one at upper centre) control which chemicals pass through to reach the capsid and its RNA. The surface proteins help the virus attach to cells.