What are Mitochondria?
A mitochondrion is commonly known as the “powerhouse of the cell”. It might be more accurate to think of mitochondria as part of the digestive system of a cell. As our digestive system, mitochondria are responsible for taking in nutrients and breaking them down in order to generate energy for the cell to use.
Specifically, mitochondria break down fatty acids and carbohydrates in order to generate ATP (adenosine triphosphate), which the cell then uses as energy-rich fuel. Complex carbohydrates must first be broken down into smaller units (like glucose) before they can be used to generate ATP. This is why it takes your body longer to break down complex carbohydrates than simple sugars.
The process that occurs inside mitochondria is called “cellular respiration”. Cellular respiration is a series of chemical reactions that take in oxygen and glucose (a type of sugar) and create energy (in the form of ATP), water, and carbon dioxide as a waste product. These chemical reactions are why we need to breathe oxygen and why we release carbon dioxide when we exhale.
Some cells in the human body must have lots of mitochondria, while a few don’t need them at all. Muscle cells are packed full of mitochondria because they require lots of energy to perform their job of moving your muscles. On the other end of the spectrum, red blood cells don’t have any mitochondria because their only job is to carry oxygen and they don’t need to produce energy on their own.
Mitochondrion: Image Source: Charles Jones (2017)
Mitochondria are some of the only organelles (with the exception of chloroplasts) that have their own internal DNA. This is because mitochondria probably originated as free-living prokaryotic cells. In the far off past, the ancestors of modern mitochondria were engulfed by a primitive eukaryotic cell. Rather than digesting the prokaryotic cell, the eukaryotic host allowed it to remain safely inside if it provided energy in return. This created a symbiotic relationship and led mitochondria to become the organelle we know of today.
Mitochondria are found in nearly all eukaryotic cells, including the cells of most plants, animals, and fungi. Without them, our cells wouldn’t be able to get energy from the food we eat. It’s startling to think that this vital organelle never would have existed if it weren’t for an ancient, unlikely partnership between a eukaryotic cell and a bacterium.
Jones, Charlie (artist). (2017). Mitochondria Cell Biology [digital art]. Retrieved from