What are Essential Nutrients?

What makes something an essential nutrient? If we cannot make it, we must ingest it, and so it is essential. Thus, the question becomes, what can't we make?

We can't make certain nitrogen-containing molecules, and we can't make certain vitamins/minerals. Let me explain the nitrogen-containing molecules here... (the vitamins and minerals are covered a bit on their own page).

Of the four types of macromolecules, two of them, proteins and nucleic acids, contain the atom nitrogen within them. Nitrogen is found in abundance in our air, as you learned back in the respiratory unit. But, although nitrogen is all around us, we cannot use it. Our bodies have no way of grabbing onto the nitrogen in our air and incorporating it into the molecules in our cells. That's a somewhat bizarre concept, isn't it? We are surrounded by nitrogen but we can't find a way to use it!

Other organisms don't find it so hard. These other organisms are mainly bacteria. People refer to organisms that can capture nitrogen and put it into molecules as nitrogen-fixing organisms. Once these nitrogen-fixing organisms incorporate nitrogen into molecules, those molecules exist for other organisms to ingest or use. Plants can take in these nitrogenous compounds (mainly in the form of ammonia) and turn them into proteins and nucleic acids. Then, animals can ingest the plants (and other animals) and recycle the nitrogen-containing molecules (proteins and nucleic acids) for use within itself.

Therefore, in order to get amino acids (which contain nitrogen) and in order to get the nitrogenous base portion of the nucleic acid, we need to ingest these items.