Antioxidant Defense Mechanisms
Start with the big picture
ROS include superoxide, hydrogen peroxide, hydroxyl radical, singlet oxygen, and peroxynitrite. Enzymatic defenses work in sequence: superoxide dismutase converts superoxide to hydrogen peroxide; catalase and glutathione peroxidase then help remove hydrogen peroxide, while glutathione reductase restores reduced glutathione using NADPH. Peroxiredoxins and thioredoxin provide additional detoxification, and the GSH:GSSG ratio can indicate oxidative stress. Other defenses include vitamins E and C, carotenoids, secondary scavengers, and proteins that bind iron or copper and limit Fenton chemistry. The Nrf2-Keap1 pathway regulates antioxidant-response enzymes, with selenium and several metal cofactors supporting specific systems. The lesson also considers dietary sources and the relationship between oxidative stress and conditions such as atherosclerosis, neurodegeneration, and cataracts.
What you'll learn
- Identify major reactive oxygen species and recognize their biological significance.
- Describe how SOD, catalase, and glutathione enzymes cooperate in ROS detoxification.
- Compare enzymatic defenses with non-enzymatic antioxidants and metal-binding proteins.
- Explain the roles of Nrf2-Keap1 and essential trace elements in antioxidant defense.
- Relate oxidative stress to selected pathological conditions and dietary considerations.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
