Cells have several different mechanisms to protect themselves against ROS. One mechanism cells utilize is their antioxidant defense system, which is primarily based on enzymatic components such as superoxide dismutase, glutathione peroxidase, and catalase. Cells also possess non-enzymatic molecules that scavenge and neutralize ROS, such as glutathione and vitamins C and E. Cells also use repair mechanisms to counteract oxidative damage to cellular components. DNA repair mechanisms correct DNA damage induced by ROS to prevent mutations. Protein repair mechanisms repair oxidatively damaged proteins through processes like chaperone-mediated refolding. Heat shock proteins act as molecular chaperones that assist in the refolding of denatured or oxidatively damaged proteins. Cells also use autophagy to remove damaged cellular components including the mitochondria and protein aggregates, which can produce ROS.