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AtmosphereA large reservoir of N₂, but chemically quite locked to most living things.
The element that helps write life
Nitrogen in living things: a small atom, a big role.
Nitrogen is in amino acids, proteins and the building blocks of DNA and RNA. But even though N₂ is abundant in the air, plants and animals mostly cannot just breathe it in and incorporate it.
Follow nitrogen into life ↓First: how does it get to us?
From air to life — with a few stops.
Most organisms cannot use atmospheric N₂ directly. Some microorganisms fix it into more accessible nitrogenous forms. Plants can take them in from the environment, and animals get nitrogen through food. Then the substance returns to the environment after the food chain and decomposition.
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MicrobesSome bacteria fix N₂ into ammonia or ammonium forms.
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PlantsRoots take up available forms of nitrogen, such as nitrate and ammonium.
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NutritionAnimals get nitrogen from plants or other animals and use it for their molecules.
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ReturnExcretion and decomposition they return nitrogen to the soil and further into the cycle.
Entry point no. 1
Roots have microbial partners.
In legumes, bacteria from the rhizobia group can settle in root nodules. Bacteria bind atmospheric nitrogen, and the plant provides them with sugars and an environment to live. This is cooperation, not free delivery in a bag.
The fixed nitrogen can then be part of the ammonium compounds and organic molecules that the plant uses to grow.
BACTERIA:
"I brought nitrogen from the air."
PLANT:
"Great. Payment in sugars, as we agreed."
"I brought nitrogen from the air."
PLANT:
"Great. Payment in sugars, as we agreed."
Entry point no. 2
Nitrogen builds molecules that work overtime.
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Amino Acids
All the common amino acids that build proteins have an amino group with nitrogen. Different side chains give them different properties.
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Proteins
Amino acids are linked together into chains that fold into proteins. These perform diverse tasks: from enzymes to structural and transport roles.
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DNA and RNA
Nucleotides contain nitrogenous bases. DNA uses adenine, cytosine, guanine, and thymine; RNA uses uracil instead of thymine.
Myth or fact?
"I breathe N₂, so I build proteins."
"I breathe N₂, so I build proteins."
Myth. Most of the molecular nitrogen we breathe in is exhaled. Our body does not only know how to use atmospheric N₂ as a direct raw material for protein. Nitrogen enters the building blocks of the body through the biological cycle and food — N₂ is not a protein milkshake.
Fun fact · genetic alphabet
DNA and RNA have nitrogen letters.
The bases A, C, G and T in DNA and A, C, G and U in RNA are nitrogenous compounds. Their sequence carries information; when expressing genes, cells use RNA and cellular machinery to make proteins.
DNA:
"I have a plan."
RNA:
"I'm taking it to the kitchen."
RIBOSOME:
"Who ordered the protein?"
"I have a plan."
RNA:
"I'm taking it to the kitchen."
RIBOSOME:
"Who ordered the protein?"
Resources for the curious
Open the textbook, not just the refrigerator.
The summaries on this page are simplified. For a more detailed explanation of the composition of proteins, nucleic acids and the role of microorganisms, see these educational resources.
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1. Which option is a molecule of ordinary nitrogen, mostly found in the air?
QUESTION 2 OF 2
2. How much dry air is nitrogen N₂?
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