Summary
Electron leakage produces superoxide and other oxidants that cause damage but also act as signals.
In depth
Superoxide arises at complexes I and III; superoxide dismutase converts it to hydrogen peroxide, which catalase or peroxidases remove. Damage to DNA, proteins and lipids is linked to ageing. ROS also act as signals.
Cells have antioxidant defences: SOD, catalase, glutathione peroxidase, vitamins C and E. Oxidative stress is imbalance.
Key idea: ROS are both harmful by-products and signalling molecules.
Reactive oxygen species (ROS) include superoxide, hydrogen peroxide and the hydroxyl radical. A few percent of electrons leak from the ETC, mainly at complexes I and III, and reduce oxygen to superoxide; other sources are NADPH oxidases, peroxisomes and radiation.
ROS damage lipids, proteins and DNA, linking them to ageing, cancer and neurodegeneration, but at low levels they also act as signals in cell growth, immune defence (the oxidative burst of phagocytes) and stress responses. Defences include superoxide dismutase, catalase, glutathione peroxidase and antioxidants such as vitamins C and E.
Example: chronic granulomatous disease arises when phagocytes cannot make ROS and infections follow.
Common mistake: more antioxidant supplements are not always beneficial, since ROS signalling is needed.
Frequently asked questions
What is Reactive Oxygen Species?
Electron leakage produces superoxide and other oxidants that cause damage but also act as signals.
Which area of biology covers Reactive Oxygen Species, and how advanced is it?
Reactive Oxygen Species is one of the 53 topics in Metabolism & Bioenergetics. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Pentose Phosphate Pathway, NAD and FAD, Warburg Effect.
Can you give an example of Reactive Oxygen Species?
Antioxidant supplements have not clearly shown benefits in trials.
What should I learn before Reactive Oxygen Species?
Work through the Beginner topics in Metabolism & Bioenergetics first, such as Metabolism, Anabolism and Catabolism, ATP, then return to Reactive Oxygen Species. Advanced topics assume the Intermediate vocabulary.
What topics are related to Reactive Oxygen Species?
The closest topics to Reactive Oxygen Species are Pentose Phosphate Pathway, NAD and FAD, Warburg Effect, Cellular Respiration. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Reactive Oxygen Species?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Reactive Oxygen Species. To practise the whole of Metabolism & Bioenergetics, use the Metabolism & Bioenergetics quiz.
How is Reactive Oxygen Species different from Pentose Phosphate Pathway?
Reactive Oxygen Species: Electron leakage produces superoxide and other oxidants that cause damage but also act as signals. Pentose Phosphate Pathway: Produces NADPH and ribose sugars for biosynthesis and antioxidant defence. Read both side by side and note what each one explains.
What is a common mistake about Reactive Oxygen Species?
More antioxidant supplements are not always beneficial, since ROS signalling is needed.
How should I study Reactive Oxygen Species step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Pentose Phosphate Pathway and explain the difference aloud. Finally, take the Metabolism & Bioenergetics quiz and come back to this page for any question you miss.