Harmful Byproducts of O2

Reactive Oxygen Species (ROS): these are dangerous and highly reactive molecules formed from a partial reduction of oxygen. 

1. Superoxide Ions: These occur when a single electron is added to O2 to generate a singular radical on one oxygen. Because of its reactivity, it can damage cells. 

2. Hydrogen peroxide: This is H2O2, or water with an extra oxygen molecule. This is also highly unstable and causes damage to cells. 

3. Hydroxyl Radicals: This is an OH that contains a radical. Radicals are very unstable, and therefore unsafe for the cell. 

Solutions

Antioxidant Enzymes: 

1. Superoxide dismutase: This converts superoxide ions to H2O2

2. Catalase: This breaks down H2O2 to H2O + O2

Glutathione System: 

1. Glutathione peroxidase: Uses 2 glutathione (GSH) molecules to reduce H2O2 to H20 + O2 which produces an oxidized version of glutathione (GSSH) by bonding the sulfur together

2. Glutathione reductase: This regenerates GSH from GSSH using NADPH