How does the human body deal with free radicals it creates itself?

Question

I know that free radicals are created all over your body all the time as a byproduct of its chemical processes, (or maybe I do not and that is false). However I am confused about the distinction between free radicals formed from UV photons that will affect DNA base pairings, and the ones that the human body creates on a consistent basis.

How does the body deal with the free radicals it created by itself?

And how are those free radicals different from the ones that cause oxidative damage (e.g., from UV rays)?

Answer 1

Reactive oxygen species, primarily superoxide, may result from one-electron reduction of molecular oxygen. Given that aerobic metabolism involves loooooong chain of electron transfers, it isn't all that rare.

Human body uses specialized enzymes to defang reactive oxygen species. The most well known are peroxidase and superoxide dismutase (see wiki for details).

Aside from this, free radical and other oxygen and nitrogen active species are, apparently, involved in some forms of immune response. In this case they are not dealt with, but instead are expected to do maximum possible local damage.

Answer 2

Some enzyme-catalyzed reactions produce free radicals as short-lived intermediates, but these are likely to be contained within the enzyme active site until they can react further to form product. Example: ribonucleotide reductase - which catalyzes the formation of deoxyribonucleotides and enables the production of DNA.

I can't think of any case where a biochemical process "intentionally" forms a free radical and then allows it to escape and cause damage elsewhere in the body. But biology is wonderfully varied and I would not want to say "never".