Chapter 10 Summary

Chapter 10.1

• Reactive oxygen species (ROS) are reactive molecules containing oxygen that are made naturally during metabolism, including cellular respiration, photosynthesis, and oxidation of fatty acids in peroxisomes.
• ROS are useful to cell function at low concentrations, but damaging at high concentrations.
• Examples of ROS include superoxide, hydrogen peroxide, and hydroxyl radicals.
• ROS can be neutralized (reduced) into nontoxic molecules via antioxidants, which include antioxidant molecules like glutathione (GSH) and antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX).
• Oxidative stress occurs when ROS production outweighs antioxidant capacity, for example at low temperatures (inhibit antioxidant enzymes) or periods following oxygen limitation (stimulate ROS production).
• ROS react with amino acids, fatty acids, and nucleotides to cause damage to proteins, membrane lipids, and DNA, respectively.

Chapter 10.2

• Redox signaling allows cells to detect oxidative stress
• ROS like hydrogen peroxide can function as signalling molecules that cause reversible covalent chemical modifications to residues of receptor proteins in signalling pathways
• Higher concentrations of ROS can cause irreversible changes to receptor proteins that activate signalling involved in the response to oxidative stress

Chapter 10.3

• To mitigate oxidative stress, cells can decrease ROS production, increase antioxidant capacity, and/or repair oxidative damage to macromolecules.
• To decrease ROS production, cells can downregulate the activity of metabolic pathways (e.g., cellular respiration) that normally produce ROS, either before or after an oxidative stress event.
• To increase antioxidant capacity, cells can increase the production or activity of antioxidant enzymes such as SOD or CAT, either before or after an oxidative stress event.
• Several enzymes can reverse minor oxidation of macromolecules. Peroxiredoxin (Prx) can neutralize lipid peroxides (and hydrogen peroxide). Thioredoxin (Trx) and Glutaredoxin (Grx) can reduce oxidized proteins.
• Minor damage to DNA bases can be repaired via base excision repair, among other pathways.