The key difference between free radicals and reactive oxygen species is that free radicals may sometimes not contain oxygen, whereas reactive oxygen species contain oxygen in them.
Reactive oxygen species are free radical compounds. But, not all free radicals are reactive oxygen species. Both of these compounds tend to react with other compounds in order to gain electrons and achieve stability.
Key Areas Covered
1. What are Free Radicals
– Definition, Types, Features
2. What are Reactive Oxygen Species
– Definition, Types, Features
3. Similarities – Free Radicals and Reactive Oxygen Species
– Outline of Common Features
4. Difference Between Free Radicals and Reactive Oxygen Species
– Comparison of Key Differences
Key Terms
Free Radicals, Reactive Oxygen Species
What are Free Radicals
A free radical is an atom, molecule, or ion with at least one unpaired valance electron. The lack of electrons makes them highly unstable and reactive. Hence, these free radicals react with other compounds to gain stability. They obtain electrons from other molecules and complete the paring of electrons. Homolytic bond fusion forms free radicals. Free radicals are paramagnetic. They possess a permanent magnetic moment due to the presence of unpaired electrons. Hence, the presence of free radicals is easy to detect with their magnetic property. Some examples of free radicals include hydroxyl (OH•), nitric oxide (NO•), nitrogen dioxide (NO2•), superoxide (O2•–), peroxyl (ROO•), and lipid peroxyl (LOO•).
A free radical can react with another free radical, but this is not very common. They mostly react with stable compounds. In fact, they are highly reactive. However, this reactivity sometimes becomes harmful to major macromolecules like DNA, RNA, proteins, and fatty acids. They react with these molecules, undergo chain reactions, and cause damage to the cell. Sometimes free radicals can be beneficial too. They help in killing pathogens and regulating cell growth.
Production of Free Radicals
Free radicals form within the body from normal cell metabolism or external sources such as pollution, medication, radiation, and cigarette smoke. Free radicals can generate in two methods: enzymatic and non-enzymatic reactions. Enzymatic reactions that generate free radicals include phagocytosis, prostaglandin synthesis, and cytochrome P450 system. To be more specific, free radicals are produced as a consequence of the ATP (Adenosine triphosphate) production by mitochondria. When free radicals are produced in large numbers and cannot be destroyed, they accumulate in the body, giving rise to a phenomenon called oxidative stress. This results in the progressive development of diseases such as autoimmune diseases, cardiovascular diseases, neurodegenerative diseases, cataracts, rheumatoid arthritis, and cancer. This accumulation of free radicals is suppressed by antioxidants which are taken in from outside or produced within the body.
What are Reactive Oxygen Species
Reactive oxygen species are unstable molecules that contain oxygen and easily react with other molecules in a cell. They are highly reactive molecules formed from diatomic oxygen molecules. They are a species capable of independent existence with one or more unpaired electrons. Examples of reactive oxygen species include alpha oxygen, superoxides, peroxides, hydroxyl radicals, and singlet oxygen.
Reactive oxygen species (ROS) are produced as byproducts during normal metabolism reactions. These reactive oxygen species can be neutralized with the reaction of certain molecules. When the generation of reactive oxygen species increases the system’s ability to neutralize and eliminate them, a certain stress condition appears; we call this oxidative stress. In addition, the excess amount of reactive oxygen species can cause damage to the biological systems. Such damage includes damage caused to cellular lipids, DNA, and proteins, which inhibit the cellular systems’ signal induction pathways and normal functioning.
Moreover, there are several beneficial effects of reactive oxygen species. In fact, they play an important role in many homeostatic processes involving metabolism, immunity, growth, and differentiation. Other benefits of reactive oxygen species include their role in proper cell development, proliferation, amplification of action of growth factors, as well as, activation of antioxidant systems.
Similarities Between Free Radicals and Reactive Oxygen Species
- Both, free radicals and reactive oxygen species, contain unpaired electrons.
- Similar mechanisms, such as exposure to environmental toxins, radiation, or other forms of oxidative stress, can generate both.
- Reactive oxygen species are free radical compounds, but not all free radicals are reactive oxygen species.
Difference Between Free Radicals and Reactive Oxygen Species
Definition
A free radical is an atom, molecule, or ion with at least one unpaired valance electron, while reactive oxygen species are a type of unstable molecule that contains oxygen and easily reacts with other molecules in a cell.
Presence of Oxygen
Free radicals may sometimes contain oxygen, whereas reactive oxygen species contain oxygen in them.
Types
There are many different types of free radicals, including oxygen-centred, nitrogen-centred, and carbon-centred free radicals. However, reactive oxygen species are a specific type of free radicals that are produced as a normal byproduct of cellular metabolism and include superoxides, hydrogen peroxides, and hydroxyl radicals.
Sources
Free radicals can be generated from a variety of sources, including environmental pollutants, radiation, and inflammation, whereas reactive oxygen species are primarily generated during cellular metabolism. But exposure to UV radiation, air pollution, and cigarette smoke can also generate reactive oxygen species.
Conclusion
Reactive oxygen species are a type of free radicals. Moreover, both types contain an unpaired electron which makes them highly reactive. There are harmful effects as well as beneficial effects of both types. The main difference between free radicals and reactive oxygen species is that free radicals may or may not contain oxygen, whereas reactive oxygen species contain oxygen in them.
Reference:
1. “Free Radicals, Antioxidants in Disease and Health.” National Library of Medicine.
2. “Reactive Oxygen Species – An Overview.” Science Direct.
Image Courtesy:
1. “Antioxidants Free radicals Lobo et al.” By Lobo, V., Patil, A., Phatak, A., & Chandra, N – Lobo, V., Patil, A., Phatak, A., & Chandra, N. (2010). Free radicals, antioxidants, and functional foods: Impact on human health. Pharmacognosy Reviews, 4(8), 118–126. (CC BY-SA 4.0) via Commons Wikimedia
2. “Respiratory burst, ROS and RNS generation in phagolysosome, March 2020” By Chloefooey – Own work (CC BY-SA 4.0) via Commons Wikimedia
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