Monday, January 30, 2017

Oxidative stress (general considerations)

Today I decided to make a post on a very important topic, oxidative stress. This subject is often referred to in biochemistry classes (and not only!), but it is not always clear to the speaker or to the audience, what it actually represents.
Nevertheless, the idea is simple to understand ... As I say many times in my classes, we have a bad habit, which kills us slowly, without exception: we spend our lives breathing oxygen! And this molecule, so important for our biochemistry, in particular for aerobic metabolism, is what kills us slowly, and makes us grow old. And do not hesitate, if we do not die of an accident, or of some illness, we will die because we have been breathing O2 during our life! :)
So, what does oxygen contain that makes it so dangerous? Basically nothing, that is, the molecule itself is harmless to our molecules/cells. The problem is in its susceptibility to suffer partial reductions, that is, to capture electrons. In fact, we are continually forming the so-called reactive oxygen species, which are essentially 3: the hydroxyl radical (free radical), the superoxide anion (free radical) and hydrogen peroxide. Of these 3, the first two are more aggressive because they are free radicals. Free radicals are molecules that have an unpaired electron (which is why they are represented with a black speckle, which is that unpaired electron).  
The electrons have a serious problem, they do not like to walk alone, so they will look for "companionship" in the first molecule that appears ahead, be it a lipid, a protein or a nucleic acid. That is, reactive oxygen species are highly reactive molecules, they are powerful oxidizing agents, which will react with our biomolecules, removing an electron and altering/destroying them. And the problem is that although the free radical ceases to be when it picks up an electron, the molecule with which it reacts becomes a free radical, giving rise to a destructive chain process.
To counteract this, our cells have several defenses, called antioxidants. Therefore, oxidative stress arises when we have an imbalance between the pro-oxidants (reactive oxygen species and reactions that produce them) and the antioxidants (processes that prevent the formation and/or action of the pro-oxidants), favoring the first, or disfavoring the seconds.