Free Radicals and Reactive Oxygen Species (ROS) || Introduction to Free Radicals

Summary

This video introduces free radicals and reactive oxygen species (ROS), explaining their definitions, types, and formation. Free radicals are molecules with unpaired electrons, while ROS are highly reactive molecules formed from incomplete oxygen reduction. The video highlights common ROS like superoxide anion, hydrogen peroxide, and hydroxyl radicals, emphasizing their roles in the body, both harmful and beneficial, such as in cellular signaling and defense mechanisms. It also covers ROS characteristics, their sources, and enzymatic reactions involved in their formation. The video ends with multiple-choice questions on free radicals and ROS.

Takeaways

• 🔬 Free radicals are molecules or molecular fragments that contain one or more unpaired electrons in their outer orbit.
• 🌬 Reactive oxygen species (ROS) are products of partial oxygen reduction that are highly reactive and play a role in biological systems.
• 💥 Examples of free radicals and ROS include superoxide anion, hydroxyl radical, nitric oxide, hydrogen peroxide, and singlet oxygen.
• 🧪 Hydrogen peroxide and singlet oxygen are not free radicals but are classified as ROS due to their reactivity.
• 🔥 Among all free radicals, hydroxyl radical is the strongest, while hydrogen peroxide is the weakest ROS.
• ⚡ Characteristics of ROS include high reactivity, short lifespan, the ability to generate new ROS through chain reactions, and tissue damage.
• 💡 Free radicals are not always harmful; they also serve functions in cellular signaling and defense mechanisms, such as nitric oxide for signaling and superoxide for respiratory bursts.
• 🔄 The incomplete reduction of oxygen leads to the formation of various free radicals and ROS, including superoxide, hydrogen peroxide, and hydroxyl radical.
• 🦠 In a respiratory burst, superoxide radicals are produced by phagocytic cells to kill bacteria, and any dysfunction in this process can lead to diseases such as chronic granulomatous disease.
• 🧬 Multiple enzymes like superoxide dismutase, catalase, and myeloperoxidase are involved in ROS management and play roles in converting free radicals to less harmful substances.

Q & A

What is the definition of a free radical?

A free radical is a molecule or molecular fragment that contains one or more unpaired electrons in its outer orbit.

What are reactive oxygen species (ROS), and why are they called that?

Reactive oxygen species (ROS) are oxygen-containing molecules that are highly reactive due to partial reduction of oxygen. They are involved in reactions in living systems, hence referred to as reactive oxygen species.

Which free radical is considered the strongest, and which reactive oxygen species is the weakest?

Among free radicals, the hydroxyl radical is the strongest. Among reactive oxygen species, hydrogen peroxide is the weakest.

What are some common sources of free radicals in the human body?

Common sources include the mitochondrial electron transport chain, normal oxidation-reduction reactions (e.g., reactions catalyzed by xanthine oxidase), flavin coenzymes in peroxisomes, amino acid oxidases, and respiratory bursts.

What role do free radicals play in the body's defense mechanism?

Free radicals, such as nitric oxide and superoxide, play a role in cellular signaling and in the body’s defense mechanisms, such as the respiratory burst that helps destroy engulfed bacteria.

Explain the difference between complete and incomplete reduction of oxygen.

Complete reduction of oxygen involves the transfer of four electrons to oxygen, resulting in the formation of water. Incomplete reduction leads to the production of free radicals and reactive oxygen species, like superoxide anion and hydrogen peroxide.

What is the respiratory burst, and why is it important?

The respiratory burst is a process where phagocytic cells engulf bacteria and produce superoxide radicals, which are then converted to hydrogen peroxide and eventually hypochlorous acid, killing the bacteria. It is crucial for immune defense.

What happens in chronic granulomatous disease (CGD) due to a deficiency in NADPH oxidase?

In CGD, phagocytic cells can engulf bacteria but cannot kill them due to a deficiency in NADPH oxidase, which impairs the production of superoxide radicals and hypochlorous acid.

How are hydroxyl radicals synthesized in the body?

Hydroxyl radicals are synthesized from hydrogen peroxide in iron-dependent reactions, such as the Fenton reaction and Haber-Weiss reaction, and are the most powerful oxygen free radicals.

What are the four characteristics of reactive oxygen species (ROS)?

The four characteristics of ROS are: (1) they are extremely reactive, (2) they have a short lifespan, (3) they generate new ROS through chain reactions, and (4) they cause tissue damage.