Cellular responses to oxidative stress in Saccharomyces cerevisiae. Oxidative stress, induced by the accumulation of reactive oxygen species (ROS) such as H₂O₂, and , can elicit a range of stress responses in budding yeast cells, that either result in cell survival (shown in green) or cell death (shown in red). Stress signals relayed by ROS themselves (such as H₂O₂) can activate transcription factors which upregulate the expression of genes encoding enzymatic (such as catalases) and non-enzymatic antioxidants (such as GSH). These response mechanisms, together with the targeted removal of small, oxidized proteins by the ubiquitin-dependent proteasome system (UPS), help ensure the survival of cells. Additionally, cells can activate cytoprotective autophagic pathways (bordered in yellow) that remove irreparably oxidized macromolecules or dysfunctional organelles, such as mitochondria. However, an abnormally high degree of autophagy might also mediate programmed cell death (PCD). Finally, exposure of cells to severe oxidative insults can elicit lethal response pathways such as apoptosis, necrosis, and possibly other forms of PCD which have yet to be discovered.