Free radical processes in living systems
Free radicals - generation in biological systems. Types of free radicals, basic reactions for formation and registration. Reactive oxygen species (ROS).
One of the major effects of Oxidative stress on biological systems is to the membrane lipids which can undergo Lipid Peroxidation (lipid forms -C=C-COO). This can result in damage to the cell membrane rendering it ineffective at separating the cellular cytoplasm and the ECM, leading to incorrect ionic concentrations and eventually cell necrosis.
Additionally membrane proteins, and DNA can undergo oxidative damage, in the case of DNA damage this can lead to mutations and eventually cancer.
Lipid peroxidation
Polyunsaturated fatty acids in membranes are the main target, because hydrogen atoms next to their double bonds are easily removed. The process is a chain reaction:
- Initiation: a radical removes a hydrogen atom from a lipid (LH), forming a lipid radical (L*).
- Propagation: the lipid radical reacts with oxygen to form a peroxyl radical (LOO*). This attacks the next lipid, forming a lipid hydroperoxide (LOOH) and a new lipid radical.
- Termination: two radicals react together, or an antioxidant stops the chain.
Peroxidation makes membranes less fluid and more permeable. Breakdown products such as malondialdehyde can also damage proteins and DNA.
Oxidative stress and antioxidant defense
Oxidative stress is an imbalance between the production of reactive species and the body's ability to remove them. It is linked to aging, atherosclerosis, neurodegenerative diseases and cancer.