Oxidation of lipids, proteins, and DNA by oxygen radicals1 (and by other free radicals2 that are formed in the process) causes their structure to become disorganized (Figure 7). Cross-linking of lipids, proteins and DNA occurs and polymers start to form. This causes major problems. Damaged proteins cannot perform their normal cellular functions and damaged DNA cannot participate in the synthesis of new proteins required to keep the cell alive. In the case of lipids, their carbon chains become truncated and “kinky” due to the loss of H atoms. Thus, the lipids no longer form a tight cellular membrane barrier and the cells and organelles become leaky. Water can enter the cells causing them to swell (edema); they die eventually by bursting. This process can take a very short time, for example, during radiation, or it can take a long time, such as after repeated use of drugs3 like methamphetamine4, or even during the aging process.
Figure 7 Watch the hydroxyl radicals (OH*) (orange circles) damage membrane lipids and proteins by removing H atoms from the lipid chains and from protein sulfhydryl groups (SH). The structure of both lipids and proteins is disturbed; the lipids become “kinky” and the membranes become leaky.
1 the reduction of oxygen by sequentially gaining electrons yields oxygen radicals such as the superoxide (O2*-) and the hydroxyl (OH*) radical. It is the OH* that damages lipids, proteins and DNA.
2 an atomic or molecular species in which 1 or more outer orbital(s) contains an unpaired (lone) electron.
3 a substance that affects the structure or function of a cell or organism
4 a derivative of amphetamine that increases the release of dopamine into the synaptic space. It causes increased alertness, restlessness and agitation.