Saturday, January 26, 2019

The Adventures of a Nitrogen Atom

From the Oxford University Press blog:
You have more than six hundred muscles in your body. Pick one of those muscles at random—say one of the eight in your tongue. Its cells will contain protein fibers. These consist of long chains of amino acids, which in turn contain nitrogen atoms. Now pick, at random, one of those nitrogen atoms. For storytelling purposes, let us refer to it as Atom. It turns out that Atom has quite a history, as do all your atoms.

You became part of Atom’s story when Atom became part of yours. This probably happened long after you were born; indeed, it is unlikely that any of the atoms in your newborn self are still with you. Those atoms have departed, only to be replaced by others. And besides the replacement atoms, many other atoms have joined you; otherwise, you wouldn’t have grown as much as you have since emerging from your mother’s womb.

Atom would have entered you as a component of the food you ate—more precisely, as part of the proteins you consumed. It might, for example, have dwelled in a piece of steak. After you swallowed that piece, its protein molecules were torn into their constituent amino acids by your digestive system. Those amino acids then entered your bloodstream and the one with Atom was subsequently taken in by a tongue cell.

The steak would, of course, have come from a cow. Before becoming part of that cow, Atom might have been part of a clover plant that the cow ate, and before that, part of an ammonia molecule that the plant took in through its roots. Previous to that, Atom would have been part of a nitrogen molecule, drifting through the air. These molecules consist of a pair of nitrogen atoms, and they are the primary component of the earth’s atmosphere.

For Atom to move from a nitrogen molecule to an ammonia molecule required some radical chemistry. It might have taken place in the reactor vessel of a fertilizer factory: in the Haber process, nitrogen molecules are mixed with natural gas and steam under very high temperatures and pressures to produce ammonia. Alternatively, the nitrogen molecule to which Atom belonged might have been struck by lightning and thereby become part of an ammonia molecule. And finally, Atom could have become part of an ammonia molecule inside one of the rhizobia bacteria that lived on the roots of the clover plant that the cow ate.

Before drifting through the atmosphere, Atom would have had many other adventures. It is conceivable, for example, that besides dwelling in you and maybe a cow, Atom might have spent time in, say, Napoleon and, long before that, in a dinosaur.

Push further back and we arrive at the moment of Atom’s “atomic birth.” Atom didn’t come into existence in the Big Bang, 13.7 billion years ago. That event yielded only hydrogen and helium atoms, along with a few lithium and beryllium atoms. The formation of other elements required the presence of stars, and the first of those would have appeared about 200 million years after the Big Bang. In those stars, hydrogen and helium fused to make heavier atoms, including nitrogen. Subsequent stars would have been even more efficient in their nitrogen production....MORE