Module 2: Figure reactive oxygen species (ROS)
Formation and metabolism of the reactive oxygen species (ROS).
To understand the properties of reactive oxygen species (ROS) and how they are formed, it is best to begin with oxygen. Oxygen is a strong oxidizing agent in that it has two unpaired electrons (e−; red dots), which have parallel spins (i.e. they spin in the same direction as indicated by the two black arrows) and occupy separate π-antibonding orbitals. Given that they have these unpaired electrons, oxygen qualifies as a free radical. However, oxygen is relatively inert because, in order to react with another molecule, it has to accept a pair of electrons with antiparallel spins to fit into the empty spaces in the π orbitals. Because of this restriction, oxygen accepts electrons (e−) one at a time and this leads to the formation of the different ROS.