By Vidya Rajan, Columnist, The Times
There are 92 naturally occurring elements in the periodic table, but only a handful of elements are essential to life. They include hydrogen, oxygen, carbon, and nitrogen in large quantities, moderate amounts of iron, magnesium, sodium, potassium, phosphorus and sulfur, and miniscule quantities of “micronutrients” like selenium and zinc. Why? In an intermittent series of articles, I will explore the functions of these elements in living organisms.
In a previous article, I examined oxygen and its functions [1]. Oxygen, as we saw, is a disposal channel for removing energy-depleted electrons from the body by combining with them to make water.
To use an analogy, food and oxygen are like the hot and neutral wires of an electrical appliance. By plugging the black wire of the electric cord into the hot socket, you are bringing in energy-rich electrons to the appliance, just as food does for your body. Your appliance, or body, sucks the energy out of the electrons to perform a function. The resultant energy-poor electrons are removed by the white wire to the neutral terminal, and back into the wall socket to return to the power plant to get refreshed with energy. This stream of energy-rich electrons that we call electricity powers your appliance.
But if you cut the white wire leading out of the appliance, electrons would pile up inside the appliance and jam the pipeline, preventing the hot wire from bringing in fresh energy-rich electrons, and the appliance would then stop working. In living bodies, food brings in fresh energy-rich electrons and oxygen removes energy-depleted electrons. Without oxygen removing the depleted electrons, they will jam the pipeline and the body will die from lack of energy. So, food – the hot wire, and oxygen – the neutral wire, have to both operate to keep the stream of energy flowing.
But what happens after those electrons get into the body through food intake? Short answer – they have to be moved around, and the energy extracted from them. Pigment molecules called chromophores do this job of binding and ferrying electrons both inside and outside the cell. The most broadly recognizable of these chromophores is hemoglobin, which binds and transport oxygen in our bloodstream. As the term “chromophore” suggests, they also have color, and their color change is a proxy for changes in oxidation states depends on whether they have more or fewer bound electrons, also known as their reduction-oxidation state, respectively. When oxygen binds, the atom’s oxidation state increases and its color changes . Iron exists in two soluble forms, an oxidized bright red ferrous (Fe2+) form and a reduced dark red ferric (Fe3+) form. This is why oxygenated arterial blood is a brighter red compared to deoxygenated venous blood.
Intracellular iron-containing chromophores called cytochromes perform important functions. These include oxidizing toxins in the liver, transporting electrons in mitochondria to make the energy molecule ATP, and absorb excess reactive oxygen species (ROS) that could damage DNA. Cytochromes in electron transport chains in the chloroplasts of algae, plants, and some bacteria, help to store the sun’s energy in organic molecules through photosynthesis. These reactions are only possible because iron has the ability to both bind and release electrons. When iron forms associations with other molecules such as enzymes or heme, the central functionality of iron to gain or lose electrons is harnessed to assist in a variety of chemical reactions.
Iron is so important for the production of energy through electron-transport chains that all living organisms need it. Iron is abundant on land, but dissolves poorly in sea water. This iron deficiency in the vast surfaces of ocean water limits phytoplankton growth. If iron could be supplied to these areas by “iron fertilization” it could increase phytoplankton levels. The hypothesis is that photosynthesis by phytoplankton would absorb carbon dioxide from the air and reduce global warming.
Iron can be leveraged by drugs can treat diseases. For example, iron in red blood cells can release oxygen which oxidizes and kills Plasmodium, the malarial parasite. The parasite blocks oxygen’s action by producing a huge amount of antioxidants. Artemisinin blocks the production of antioxidants by Plasmodium, and is now the last drug effective for malarial treatment. Artemesinin’s complicated and elaborate mechanism was only fully elucidated in 2020. Malaria kills more people than any other parasitic disease in the world, and iron and oxygen work together to kill the malarial parasite. This is ironic. It is also poetic justice since Plasmodium consumes the heme protein of red blood cells, releasing its adversary iron in the first place.
Iron has other corporeal functions too. Magnetic particles made of magnetite, Fe3O4, help some animals to orient and navigate using the Earth’s magnetic field, and they have been found in bees [2]. Magnetite particles have also been found in bacteria, in mollusks, turtles, birds, and many mammals. Humans have magnetite in the brain, liver, heart, and spleen, but whether they are functional is not known for certain [3].
So, iron can be an energy-producer, drug-enhancer and path-finder. It can also anchor a joke: What’s the difference between “male” and “female”? The answer is Fe, the chemical symbol for iron. Females are males with added iron, for extra strength, ductility, and magnetism.
Worker (female) bees, I bet you like that joke.
References
- Rajan, V., Inner Nature: The Breath of Life, in The Unionville Times. 2019: Kennett Square, PA.
- Kuterbach, D.A., et al., Iron-containing cells in the honey bee (Apis mellifera). Science, 1982. 218(4573): p. 695-697.
- Servick, K., Humans may sense Earth’s magnetic field. 2019, American Association for the Advancement of Science.
