Complex sentence: ROS are produced as a normal product of cellular metabolism, in particular, one major contributor to oxidative damage is hydrogen peroxide (H 2 O 2) which is converted from superoxide that leaks from the mitochondria.
Split into simpler sentences: ROS are produced as a normal product of cellular metabolism. In particular, one major contributor to oxidative damage is hydrogen peroxide (H 2 O 2) which is converted from superoxide that leaks from the mitochondria.