The Crucial Roles of Nitrogen and Oxygen in Biochemistry

By Ron B. Davis Jr.Georgetown University

That nitrogen and oxygen are important in many biological reactions is undeniable. Oxygen’s ability to make two bonds helps it to incorporate into large molecules. And the geometric complexity that comes with the ability to form branches makes nitrogen truly special. As an example, we find nitrogen showing off this ability in the connections made between our DNA base pairs and the backbone holding them in place.

Fertilizing the garden using nitrogen rich fertilizers
Adding nitrogen to soil can help make plants grow healthier and stronger. (Image: Simon Kadula/Shutterstock)

The Importance of Nitrogen to Life

Because halogens and oxygen have higher reactivities, they are easily inserted into a range of important and useful compounds, whether through biological or non-biological reactions. But nitrogen is more challenging. Nitrogen from our atmosphere is in its diatomic form, and is practically inaccessible to most living things. 

It was even inaccessible to human technology until just about a century ago. Because it is so stable and content in its pure diatomic form, nitrogen in combination with other elements, or so-called ‘fixed nitrogen’ is quite a challenge. But nitrogen is essential to life. It appears in key biomolecules we rely on to stay alive, like the bases of our DNA and the amino acids that make up essential proteins and enzymes.

The Role of Nitrogen in Agriculture 

Portrait of Justus von Liebig
German scientist Justus von Liebig’s suggestion ultimately led to the development of chemically manufactured fertilizers. (Image: Wilhelm Trautschold/Public domain)

By the 1820s, it was already understood that nitrogen is one of the elements crucial to proper plant health. Justus von Liebig, a German chemist and survivor of the famine following the 1816 ‘year without a summer’ in Europe, suggested that by replacing missing nutrients like nitrogen artificially, plants could be made to grow stronger, healthier, and more productive, and maybe the next famine could be averted. 

It was this insight that ultimately led to the development of chemically manufactured fertilizers—a major global industry and the primary reason that the world has enough food to support 8 billion human inhabitants today.

But throughout the 1800s, sources of fixed nitrogen remained scarce. Usable nitrogen had to be obtained from minerals or biological material that already contained nitrogen bonded with other elements. But wouldn’t it be nice if we could somehow borrow nitrogen from our atmosphere where it is so abundant to make nitrogen compounds? 

In a roundabout way, we have done this for millennia. Certain microorganisms that live on the roots of beans and other plants have the very special ability to break the nitrogen triple bond and incorporate atmospheric nitrogen into their biomass, which is passed on through the food web. In fact, human agriculture had been exploiting that ability for quite some time as well in the form of crop rotation, planting products like soy every few years in place of other crops to help replenish the usable nitrogen in the soil.

This article comes directly from content in the video series Understanding the Periodic TableWatch it now, on Wondrium.

How to Use Atmospheric Nitrogen to Produce Ammonia 

But, what if we didn’t even have to do that? What if we could grow what we needed, where we needed it, every growing season? In the 20th century, that largely became possible because of a familiar chemist, Fritz Haber.

Ammonia tank against the blue sky
Ammonia is produced when nitrogen and hydrogen are combined under extreme heat and pressure. (Image: Robert Kyllo/Shutterstock)

In the second decade of the 1900s, Haber devised a way to convert atmospheric nitrogen into ammonia by combining it with hydrogen under immense pressure and heat. Under those extreme conditions, the energy from the intense heat is able to break the nitrogen triple bond. 

Meanwhile, the high pressure promotes the formation of ammonia, which is a liquid that can be collected and used to produce a wide range of nitrogen-containing products. In 2018, the Haber-Bosch process was responsible for the production of more than 200 million tons of ammonia, most of which is used as fertilizer.

Oxygen and Nitrogen: Elemental Superstars

By now we know that elemental oxygen strikes a wonderfully useful balance between stability and reactivity—stable enough to remain available in the air for long periods of time, but also reactive enough that we can harness its chemical potential in burning fuels and powering our bodies.

And yet, shepherding energy is just one of many important roles played by oxygen in the chemistries inside and around us. In fact, oxygen and nitrogen are both part of the short list of biological elemental superstars of life. The reason that these two elements are among those elements indispensable to life goes back to the abundance and complexity of these two elements.

Oxygen Inside and Around Us

Oxygen is currently 21% of our atmosphere, but it took early photosynthetic life a long time to get us here. For more than one and a half billion years, diatomic oxygen was getting produced by primordial organisms, but then getting captured in sea rocks, later by land rocks and finally by reacting with methane in the primordial atmosphere.

It was only after vast amounts of diatomic oxygen had bonded with most of the easy dance partners in the environment that oxygen finally began to accumulate in the atmosphere, starting roughly 850 million years ago.

Once this stage was reached and oxygen began to build up in the atmosphere. Respiration became an effective metabolism, and larger and larger organisms started to emerge, eventually leading to the evolution of higher animals.

Common Questions about the Crucial Roles of Nitrogen and Oxygen in Biochemistry

Q: Why is nitrogen crucial to life?

While oxygen and fluorine are very reactive and can easily be involved in many chemical reactions, nitrogen is very stable in its pure form. Despite this, nitrogen is strikingly essential to life and it appears in many key biomolecules like the bases of our DNA. Nitrogen also appears in the amino acids responsible for making up enzymes and proteins.

Q: What did Justus von Liebig suggest to make plants grow healthier?

The role of nitrogen in agriculture as a vital element to plant health was understood by the 1820s. German chemist and survivor of the famine, Justus von Liebig, suggested that by artificially adding nutrients such as nitrogen to soil, plants would grow healthier, stronger, and more productive. This suggestion led to the development of fertilizers, and consequently, the production of enough food for Earth’s population.

Q: How was ammonia produced by Fritz Haber?

Combined with hydrogen, nitrogen could be converted to ammonia under immense heat and pressure. This was proposed by Fritz Haber in the 20th century. In fact, the heat produced from those extreme conditions is able to break nitrogen bonds, and the extreme pressure helps the formation of ammonia. The liquid ammonia is used to produce a wide range of fertilizers, proving how important is the role of nitrogen in agriculture.

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