Free radical cellular damage. Conceptual animation showing free radicals damaging cells. Free radicals are molecules that contain unpaired electrons (bright spheres), making them highly reactive. They are a by-product of a number of biochemical reactions that occur in the body. They cause damage to various cellular components, including cell membranes as seen here, by stealing an electron to complete their pair. Accumulation of damage by free radicals can lead to cellular death.HD master is flattened onto a black background, as seen in this preview. The original file has a transparent alpha channel and is available as the HD master of clip K003 3739.