OXYGEN

British biochemist Lane (University College, London) examines questions of life and death as seen through the lens of oxygen.

The multidisciplinary text begins with Earth’s primordial environment, in which the main source of atmospheric oxygen was the breakdown of water exposed to ultraviolet light. Much of this aboriginal oxygen either escaped into space or reacted with other elements to form mineral oxides. Early life evolved largely free of atmospheric oxygen, although LUCA, the Last Universal Common Ancestor of current life some 3.85 billion years ago, used oxygen to generate energy. The atmosphere began to gain large amounts of oxygen when certain cells learned to photosynthesize their food from carbon dioxide and water, with oxygen as a waste product. Shortly thereafter (in evolutionary terms) another type of cell developed the complementary strategy of respiration, which uses oxygen to extract energy from foods. But oxygen, as every chemist knows, is a dangerously reactive element. Living creatures make special efforts to avoid direct contact with it, using special enzymes, physical shielding, and other tricks to keep its concentration within their bodies at a safe level. Even sexual reproduction can be shown to be a partial defense against oxygen damage, especially in the restriction of mitochondria (which regulate the use of oxygen) to the cells donated by the mother. Damage to DNA caused by oxidative stress appears to explain aging and many of its diseases, hence the popularity in alternative health circles of antioxidants. But antioxidants alone fail to prevent aging. Lane suggests two different avenues of study: modulation of the immune system, which generates free radicals as part of its defense against infectious diseases; and ways of improving the health of our cellular mitochondria, on which many age-related ailments seem to depend.

Provocative and complexly argued.