This illustration provides a 3D graphical representation of a spherical-shaped, measles virus particle that is studded with glycoprotein tubercles. Those tubercular studs colorized maroon, are known as H-proteins (hemagglutinin), and those colorized gray are referred to as F-proteins (fusion). The F-protein is responsible for fusion of virus and host cell membranes, viral penetration, and hemolysis, and the H-protein is responsible for binding of virus to cells. Both types of proteinaceous studs are embedded in the envelope’s lipid bilayer. (Image via the US Centers for Disease Control and Prevention's Public Health Image Library