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.