Final answer:
Free radicals produce more free radicals during oxidation reactions, leading to a propagation cycle that contributes to aging, rancidity in fats, and cardiovascular diseases.
Step-by-step explanation:
Free radicals produce more free radicals while causing oxidation reactions. When oxygen, which is a diradical, adds to a free radical in the hemolytic bond-making step, it produces a new radical. This new radical then abstracts allylic hydrogen from another fatty acid, thus propagating the cycle of radical formation.
This series of propagation reactions results in the installation of hydroperoxyl groups on the fatty acids, ultimately leading to the breakdown of these unstable hydroperoxides into short-chain aldehydes and carboxylic acids, which give aged fats an unpleasant rancid smell.
These reactions also play a role in cardiovascular diseases due to the oxidation of low-density lipoproteins in arteries. Even broader, the aging process in organisms is postulated to be linked to these kinds of free radical reactions. Reactive oxygen species (ROS), such as hydroxyl radicals OH, H₂O₂, and superoxide (O₂), consist of highly reactive free radicals produced during normal cellular processes including ATP production via mitochondria and oxygen metabolism.
ROS are known not only for their damaging effects, causing cellular damage and possibly cell death, but also for their essential roles in cell signaling processes and immune responses against pathogens. Due to their unpaired electrons, they easily oxidize other molecules, contributing to various destructive processes in the body, such as cancer and coronary artery disease.