What Is Mitochondria? - Definition & Functions

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  • 0:05 Mitochondrion
  • 0:36 What are Mitochondria?
  • 2:21 Mitochondria: Functions
  • 3:57 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
What does a little thing inside of your cells have to do with bacteria, energy, money, and your body's life sustaining processes? Well, in one word, 'mitochondrion' is the answer! In this lesson, you will learn about mitochondria and their function.


Once upon a time, long before you were born, there was a little bacterium who was christened Mitochondrion, or Mito for short. Mito was mighty small and was always running away from bigger and badder cells. One day, he was eaten by a big cell. Poor, Mito! You might be wondering; did Mito die?

Actually no, something else happened. But what is it? Who was this little Mito? And what does he do for a living now? It's a mystery we're about to solve.

What Are Mitochondria?

In the annals of history, scribes have theorized that Mito and his kind, the mitochondria, were likely once free-living bacteria that eventually came to inhabit larger and more complex cells called eukaryotic cells in a mutualistic relationship that gave mitochondria food and protection and the host eukaryotic cells extra energy for their own functions and survival.

The mitochondria are now double-membraned organelles that exist within a eukaryotic cell's cytoplasm, the types of cells that make up our body. The cytoplasm is gel-like and located inside a cell's plasma membrane but outside of the nucleus. And an organelle is simply a membrane-bound structure responsible for a specific function within a cell.

Remember, Mito was mighty small and lots of things, like bigger bacteria, could easily kill him. One day, his luck ran out, or so he thought, and a bigger cell engulfed him. Mito should have died. But, by golly, Mito survived! The bigger cell could not digest him. By a stroke of luck, instead of dying, Mito realized he was stuck inside a big cell that had a lot of food floating around; food that he munched on voraciously. It was also a bigger cell that protected him from some predators that would have killed him for sure. So, Mito found a new home and a new source of food. Who would try and leave that?

In exchange for all that food and protection, Mito repaid his host cell with money like we would any nice bed and breakfast. No, really. Mito exchanged cold hard energy currency for food and board. Once inside the eukaryotic cells, he began to repay his landlord and restaurant, the eukaryotic cell, with a specific kind of energy currency.

Mitochondria: Functions

This energy currency, called adenosine trisphosphate (ATP), is produced by the mitochondria in our body's cells. Think of a mitochondrion, single for mitochondria, as the Department of the Treasury in the U.S. that designs and prints money, as a well as a power plant, all rolled into one little organelle. This energy currency helps pay for and drive our body's many functions including our movement, our heartbeat, and the synthesis of many molecules necessary for our survival.

The way it works, in a jiffy, is that parts of the food we eat are converted by the mitochondrion into ATP much like parts of a tree are converted into paper money. The process by which mitochondria produce ATP is called alternatively the citric acid cycle, Krebs cycle, or tricarboxylic acid (TCA) cycle; take your pick.

So you see what happened here with little Mito? He got saved from the outside world by accidentally setting up shop inside a eukaryotic cell but he also helps sustain his home's life and processes as well by producing lots of ATP!

But mitochondria have other functions, beyond just energy production. They are involved in:

  • Apoptosis, which is a fancy word for a controlled and orderly programmed cell death. So if a cell is sick it might commit apoptosis to spare nearby cells from getting sick
  • The synthesis of steroids
  • Cell signaling pathways

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