Nitrogenase: Structure, Role in Nitrogen Fixation & Activity

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  • 0:00 Nitrogen Fixation
  • 0:42 Nitrifying Microbes
  • 2:11 Structure & Activity
  • 3:27 Lesson Summary
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Lesson Transcript
Instructor: Brekke Peterson Munks
This lesson will define and explore the activity, structure and importance of the enzyme nitrogenase. You'll also learn about the nitrifying bacteria found in some of the foods you eat every day.

Nitrogen Fixation

Nitrogen fixation is a natural process where nitrogen gas is converted into ammonium either by microbes or by lightning. The process is vital to life on the planet and food production, as nitrogen is needed for biomass production. Nitrogen fixation would not occur without a special enzyme called nitrogenase, an enzyme found in some types of nitrifying microbes that allows for the reduction of nitrogen gas to ammonium.

There are two main forms of nitrifying microbes: symbiotic nitrogen fixing bacteria and free-living nitrogen fixing bacteria.

Nitrifying Microbes

1. Symbiotic nitrogen fixing bacteria live on plants and are found around the world. They are most commonly associated with Rhizobia bacteria that live on a class of plants called legumes (which include the pinto beans on your burrito, chickpeas in your hummus, soybeans in your tofu, and green peas in your salad). These bacteria live in nodules on the roots of the plants, which look much like little pearls, for protection from the outside world. Nitrogenase is incapable of functioning when oxygen is present. The plant provides simple sugars to the microbe, and in return, the plant receives the excess nitrogen fixed by the microbe.

Frankia bacteria can also fix nitrogen through symbiotic relationships with some trees and shrubs, like birches, roses, and Australian pines. These bacteria also live in root nodules.

Some cyanobacteria also have symbiotic relationships with some hornworts, liverworts, mosses, horsetails, ferns, cycads, lichens, and other plants. These bacteria have special cells called heterocysts, which do not carry out oxygen reactions in photosynthesis, allowing nitrogen fixation to occur.

2. Free-living nitrogen fixing bacteria do not require associations with other organisms to survive. These include some cyanobacteria and green, purple, and non- sulphur bacteria. Cyanobacteria fix over half of the nitrogen found in marine ecosystems.

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