Many phenomena initiate free radical formation within the
body. Although such things as environmental pollutants and
radiation are direct and indirect sources of free radicals, the primary
source is endogenous from normal oxidative metabolism
in mitochondria. The body defends itself against the effects of
free radicals through a complex of protective antioxidant compounds.
These compounds protect biomolecules by scavenging
free radical compounds, minimizing free radical production and
binding metal ions that might increase the reactivity of poorly
reactive compounds. Besides these classic mechanisms, many
antioxidants exhibit second messenger regulatory function, cell
cycle signaling and control of gene expression (Chapter 7 covers
antioxidants in detail).