Osteoblasts. Coloured transmission electron micrograph (TEM) of osteoblasts, bone-producing cells (purple and pink). They contain rough endoplasmic reticulum (RER), which produces, modifies and transports proteins, and a nucleus, which contains the cell's genetic information. Mitochondria provide the cell with energy. The cells produce the collagen, or osteoid, that provides the framework for the mineralised matrix of bone (bottom). Magnification: x3000 when printed 10 centimetres wide.