Mitochondria: More than just power plants for your cells

Chris Chen
13 March 2016

Above: Diagram of an eukaryotic cell’s mitochondrion (Mariana Ruiz Villarreal, Wikimedia Commons)

Have you ever wondered exactly where your body gets the energy it needs to work? Your body is made up of more than 30 trillion cells, and most of them contain small organelles called mitochondria. These tiny power plants constantly produce energy by converting oxygen from the air you breathe into carbon dioxide. Mitochondria also turn the food that you eat into energy for the cells located all over your body. Without mitochondria, you would not survive.

But it turns out that mitochondria are more than just sources of energy. Over the last ten years or so, researchers have discovered how mitochondria actually play a variety of different roles. For example, it turns out that they can increase energy production by joining together with other mitochondria. And they even contain their own specialized DNA!

Did you know? Apoptosis (cell death) is an ongoing process in your body. It targets low-performing cells for removal, while allowing better functioning cells to live on. Survival of the fittest!

High and low energy demand

When you do things like walk up a long flight of stairs, you use quite a bit of energy. And when energy demand is high, mitochondria respond with cellular respiration. That is when cells in your body start consuming oxygen to convert food into energy.

If the demand for energy remains high—for example, if you regularly swim laps in the pool for several weeks—mitochondria can join together to form larger structures within the same cell. This process is called mitochondrial fusion and it can increase the functional capacity of mitochondria. That means the mitochondria can generate more energy, while also converting food into energy more efficiently.

Another way that mitochondria increase their efficiency is by synthesizing (producing) new proteins through a process called biogenesis. Mitochondrial biogenesis and fusion both occur after endurance exercise. So if you were training for a marathon, you would end up with more mitochondria in your muscles, causing them to work more efficiently.

The opposite occurs when energy demand is low: you end up with fewer mitochondria, less fusion, and no biogenesis. For instance, this could happen if you broke your arm and it stayed in a cast for several weeks. This prolonged period of inactivity would actually cause the bone and muscles to shrink, a condition called muscle atrophy.

Muscle atrophy is actually a big problem for astronauts. Due to a lack of gravity in space, they often suffer muscle and bone loss. This is partly because their mitochondria are not generating very much energy. Without energy, many cellular processes start shutting down, so muscle and bone mass are no longer maintained. At the same time, mitochondria become increasingly smaller through fission—the opposite of fusion—and they respire less.

When tissues like bones and muscles remain unused for very long periods of time, mitochondria also start to release reactive oxygen species (ROS) that damage cellular components like DNA and proteins. Over time, the production of ROS will stop cells from working properly. At a certain point, mitochondria will trigger apoptosis. That means they intentionally cause the cell to be be destroyed. Who knew mitochondria were so powerful?

Did you know? Mitochondrial DNA, which contains instructions for your cells to produce energy, is always inherited from your mother’s side. Another reason to celebrate Mother’s Day!

Mitochondrial DNA

Mitochondria also contain their own DNA. To function properly, mitochondrial DNA code for the protein complexes necessary for generating energy. These large protein complexes are located inside of mitochondria, in something call the respiratory chain.

When mutations occur in mitochondrial DNA, they can prevent the mitochondria from working properly and cause mitochondrial diseases. A small change in mitochondrial DNA can have a big effect on organ function. For example, if an A is changed to a G in a specific part of the DNA sequence, it can cause maternally inherited diabetes and deafness (MIDD). This mutation produces a change in a specific amino acid responsible for the synthesis of new proteins.

Did you know? Resistance exercises, like lifting weights, increase muscle mass through a process called hypertrophy. By contrast, endurance exercises, like distance running, increase mitochondrial levels so your body can produce energy more efficiently.

So the next time you come across mitochondria in your biology textbook, remember that they are more than just tiny power plants. Mitochondria are highly dynamic structures in your cells that play a number of different roles. They respond to energy demands in your body by undergoing fusion and fission. They can increase their numbers through biogenesis and decrease them through apoptosis. Thanks to new research, the complexity and importance of mitochondria are finally becoming clear!

Learn More!

Websites with general information on mitochondria and mitochondrial disease:

Five things that happen to your body in space (2016)

About mitochondrial disease - Mito FAQ (2016)

Mitochondrial Fusion and Division (2010)
K.G. Hales, Nature Education 3

Example of a scientific study related to mitochondria:

Mitochondrial biogenesis in striated muscle (1994)
D. A. Hood, A. Balaban, M. K. Connor, E. E. Craig, M. L. Nishio, M. Rezvani & M. Takahashi, Canadian Journal of Applied Physiology 19

Chris Chen

Chris obtained a bachelor of science degree with honours and then a masters in Science from the University of Toronto. He just started his PhD degree in Kinesiology at York University and is currently studying mitochondrial function in aging and exercising muscle. In his spare time, he enjoys jogging, swimming and playing on his violin.

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