40 Interesting Mitochondria Facts: Structure, Function, mtDNA

by Sankalan Baidya
mitochondria facts

By now you must have understood at least one thing – we are going to produce facts about each and every component of a cell – be it animal cell or a plant cell. We have already covered Cell Membrane facts and we have also covered Cytoplasm facts.

It is now time to move on to other components of a cell. So, we have decided to start with Mitochondria facts. Mitochondria is popularly known as the POWERHOUSE of a cell. But why so? Let us find out!

While we will obviously answer that question, we will also ponder on various other questions that are usually connected with this essential cell organelle. Let us begin…

Name MitochondriaOriginated from two Greek words – Mitos and Chondros. Mitos means thread and Chondros means granule
ColorBrownish red – only part of cell that is colored
Size0.5 micron to 1 micron in animal cells
Present InBoth Animal and Plant cells
Present InAll Eukaryotic cells
GenomeMitochondria has it own Genome and DNA
mtDNAMitochondrial DNA is circular
CapabilityCapable of self dividing when needed

Interesting Mitochondria Facts: 1-5 | What is Mitochondria?

1. Mitochondria is an organelle present inside a cell. What type of cell? It is present in each and every Eukaryotic cell (eukaryotic cells are the ones that have a nucleus as opposed to prokaryotic cells that do not have a nucleus). Every cell in a body has Mitochondria.

2. Inside an Eukaryotic cell, the Mitochondria is found in the Cytoplasm. One thing you need to know is that the term ‘Mitochondria’ is actually plural. The singular is called ‘Mitochondrion’.

3. This brings us to a very important question. How many Mitochondria are present in a cell? Well, the number varies. The number of Mitochondria present in a cell is dictated by two factors – the type of organism in question and the type of tissue concerned.

4. For instance, complex organisms will have more Mitochondria in a cell compared to less complex organisms. Again a tissue in an organisms body will also define the number of Mitochondria present in each cell of the tissue. Not clear? Read on…

5. Mitochondria are known as powerhouses of a cells. They produce the energy that a cell requires to carry out the functions of a cell. So, if a tissue is designed to do extensive work (such as the muscle tissues in humans), the cells in the tissue will have more Mitochondria. So, just how many Mitochondria are present in a cell? The number can be as small as a single Mitochondrion in a cell to several thousand Mitochondria in a single cell.

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Interesting Mitochondria Facts: 6-10 | Structure of Mitochondria

6. Coming to structure of Mitochondria, these organelles have a complex structure. If you want to know the shape and size of Mitochondria, no one can give you a proper answer. This is because, Mitochondria can vary significantly in both shape and size.

7. But in general, Mitochondria are roughly oval in shape. However, it is interesting to know that irrespective of the shape and size, the overall makeup of the organelle remains the same. Each and every Mitochondrion possesses a double membrane.

8. The first layer of membrane – usually referred to as the Outer Membrane – is the protective layer that protects the innards of a Mitochondrion. Whether a Mitochondrion has a round blob-like appearance or whether it has the shape of a long rod, the outer membrane will be there. This outer membrane is smooth.

9. Inside the outer membrane, there is another membrane that is known as the Inner Membrane. This inner membrane is unique in the sense that it is not present in other cell organelles. And again, the inner membrane is wrinkled and folded. It actually folds over several times!

10. But why are these folds present in the first place? Why can’t the inner membrane be smooth like the outer membrane? Excellent question! Here is your answer: The folds are designed to increase the surface area.

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Interesting Mitochondria Facts: 11-15 | Structure of Mitochondria

11. What is the need for increased surface area? Imagine your classroom. What happens if the size of the classroom is reduced? Fewer numbers of students can be accommodated in the class. The folds of the inner membrane increase the surface area and provide more space for chemical reactions.

12. This means, more chemical reactions can take place. If the inner membrane was smooth, the number of chemical reactions that could take place would have reduced significantly because of less availability of surface area. In this context we need to say that there are many chemical reactions that take place on the inner membrane.

13. Then there are Cristae inside the Mitochondria. What really are those things? They are nothing but the folds that are made by the inner membrane of the Mitochondria. These Cristae actually increase the surface area.

14. There is a space between the outer membrane and the inner membrane. This space is known as the intermembrane space.

15. The space between the inner membrane is filled with a fluid. This fluid is known as the Matrix. Most of the proteins that are found inside the Mitochondria are present in the Matrix. So no, Matrix is not a movie. The Matrix is made of water and enzymes (basically proteins).

mitochondria facts
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Interesting Mitochondria Facts: 16-20 | Function of Mitochondria

16. Mitochondria generates energy that is used by cells to perform all functions. This basically means that everything that an organism does is because of the energy produced by the Mitochondria. This is the reason why Mitochondria is known as the powerhouses of cells.

17. How is this energy produced? The food that organisms eat contain chemical energy that needs to be converted into usable energy. It is the job of the Mitochondria to do so. The carbohydrates (glucose) and fatty acids that are consumed by organisms (such as ourselves) is converted in chemical energy by Mitochondria.

18. The carbohydrate that organisms consume is first broken down into what is known as pyruvate. This happens outside the Mitochondria. It is this pyruvate that then enters inside Mitochondria. Fatty acids on the other hand enter Mitochondria directly.

19. Once inside the Mitochondria, the pyruvate and fatty acids are converted into acetyl-CoA. Acetyl-CoA is a type of molecule that is produced by the organelle (Mitochondria) using the enzymes that are present in the matrix.

20. Once the acetyl-CoA is produced, it becomes the starting point for a second type of chemical reaction which is known as the ‘Citric Acid Cycle’. The other name of this second type of chemical reaction is ‘Krebs Cycle’.

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Interesting Mitochondria Facts: 21-25 | Function of Mitochondria

21. In the Krebs Cycle of the Citric Acid Cycle, the carbon atoms present acetyl-CoA are used for producing CO2 (Carbon Dioxide) through oxidative metabolism (that is metabolism using oxygen). CO2 is a waste product and hence released out of the cell. The most important thing that this Krebs Cycle does is it produces very high energy electrons.

22. The high energy electrons then reduce two enzymes called NAD+ and FAD and convert them into NADH and FADH2, which are also enzymes. One thing to note here is that NAD+ and NADH are coenzymes. Similarly, FAD and FADH2 are also coenzymes. They are called coenzymes because the former is oxidized form while the later is reduced form. So, NAD+ and FAD are oxidized forms while NADH and FADH2 are reduced forms.

23. The carrier enzymes (the reduced forms, that is, NADH and FADH2) are then transported from the matrix of Mitochondria to the inner membrane of Mitochondria. Once they reach the inner membrane, a third chemical reaction starts. This chemical reaction is known as Oxidative Phosphorylation.

24. In Oxidative Phosphorylation, the carrier enzymes give up the electrons. Once they give up the high energy electrons, they return to their oxidative states that is, NAD+ and FAD. The electrons that are released then pass through Electron-Transport Chain (present in the inner membrane of the Mitochondria) and go to oxygen (which is the final electron receptor).

25. Now, inside the Electron-Transport Chain, there are several electron acceptors. These acceptor molecules gradually strip the high energy electrons of their energy in what is known as controlled release of free energy.

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Interesting Mitochondria Facts: 26-30 | Function of Mitochondria

26. When the high energy electrons pass through the Electron-Transport Chain and lose energy, they produce what is known as ‘electrochemical gradient’ across the inner membrane of Mitochondria.

27. It is this electrochemical gradient that provides all the energy (stripped from the electrons) for production of Adinosine Triphosphate (ATP). ATP molecules are basically the energy molecules that are used by the cells.

28. The energy in the electrochemical gradient is used for converting Adinosine Diphosphate (an organic compound) and Pi (inorganic phosphate) into ATP (an organic compound).

29. This conversion from ADP + Pi into ATP actually uses 5 different respiratory-chain enzyme complexes (which form the Electron-Transport Chain). Of these 5 complexes, the first 4 are used for transporting electrons all the way up to molecular oxygen that organisms breathe in. The last complex (that is, the 5th complex) is the one that converts ADP + Pi into ATP. Wondering what those 5 complexes are called? They are known as:

  • Complex I (NADH dehydrogenase)
  • Complex II (Succinate dehydrogenase)
  • Complex III (Cytochrome-c reductase)
  • Complex IV (Cytochrome-c oxidase)
  • Complex V (ATP synthase)

30. Yet another function of Mitochondria is to control calcium ion (Ca2+) concentration in the cells. For this, the Mitochondria and the Endoplasmic Reticulum need to work very closely for limiting calcium amount in cytosol. The other functions of Mitochondria include:

  • They control cell cycle.
  • They control cell growth.
  • They are involved in signaling.
  • They are also involved in cell differentiation.
  • They are involved in the process of cell death.
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Interesting Mitochondria Facts: 31-35 | DNA of Mitochondria

31. Here is one of the most baffling Mitochondria facts for you! Mitochondria have their very own DNA that is separate from the DNA of the organism in whose cells Mitochondria are found. They also have their own ribosomes!

32. The DNA of the Mitochondria along with the ribosomes are present in the matrix of the Mitochondria.

33. The Mitochondrial DNA or mtDNA is responsible for synthesizing proteins for their own use without using other components of the cells. The mtDNA is a circular strand.

34. It is this circular DNA strand of Mitochondria that allows them to divide quickly by first growing larger in size and then dividing to increase the number of Mitochondria in a cell. This happens when cells require more energy. In case the energy requirement of cells reduce, the excess Mitochondria will simply die.

35. The presence of separate Mitochondrial DNA or mtDNA has led many scientists to believe that Mitochondria are separate symbiotic bacteria that live inside the cells. As a matter of fact, Mitochondrial genome is very similar to bacterial genome.

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Interesting Mitochondria Facts: 36-40 | Mitochondria Fun Facts

36. Many scientists say that Mitochondria are endosymbionts. Meaning? The theory says that many millions of years ago when life first evolved on Earth, oxygen was not there. So, the first organisms used anaerobic respiration. They were not efficient in ATP production.

37. Several million years later plants and trees came by and produced oxygen. That is when primitive Eukaryotic cells with aerobic respiration came to existence. They were efficient in ATP production. These Eukaryotic cells were then swallowed by other host Eukaryotic cells that were dependent on anaerobic respiration.

38. Instead of digesting these new breed of Eukaryotic cells capable of aerobic respiration, the host cells made them permanent members and started a symbiotic relationship where the swallowed cells produced ATP very efficiently allowing the host cells to use the ATP. In return, the host cells provided a constant source of food (proteins encoded in the nucleus by the genes and then synthesized in cytosol that are finally sent to the Mitochondria) for the swallowed cells.

39. Sperms have Mitochondria responsible for motility of the sperms. However, once a sperm fertilizes the egg cells, the Mitochondria of sperm are destroyed. This means that mtDNA that is found in offspring actually come from the mother’s side. In very rare cases mtDNA from a male will enter into offspring.

40. Mitochondria have brownish red color. In case melanin was absent in human skin, humans would have been of the color of Mitochondria because the only colored part present in a cell are the Mitochondria.

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Sources: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12

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Tom Kennedy March 21, 2019 - 3:52 am

Interesting facts, but several mistakes
Facts 21-25: Krebs cycle, not Kerbs cycle
Facts 36-38 is totally wrong and misrepresents endosymbiosis. Prokaryotes evolved both photosynthesis and aerobic respiration, not trees. Endosymbiosis occurred when two prokaryotes merged (an aerobically respiring bacteria and an archean), from there eukaryotes evolved. A primitive eukaryotic cell did not engulf another cell. I made a youtube video disproving this common misconception of endosymbiosis

Sankalan Baidya
Sankalan Baidya March 21, 2019 - 11:10 am

Thank you Tom for pointing out the mistake of Krebs Cycle. It has been fixed. It was a typo. However, for facts 36-38, you said that the concept was totally wrong. Can you please cite some authentic sources that say the exact same thing you said here and the video? I went through your video and you did not mention any sources whatsoever. No hard feelings but, unless you provide sources (few scientific studies) dispelling the existing notion, what you say boils down to mere opinion that you hold. You may be right but unless there is enough evidence in form of scientific studies to back your opinion, I will keep 36-38 the way it is for now.

Della April 21, 2020 - 8:11 am

I agree with Tom, a very interesting read of the overview of the mitochondria. I like it because easy to read and if you have studied cellular respiration in high school, this is a great way to pull the information together.
I also agree with Tom with respect to the endosymbiosis. From this link below I can quickly show you the authentic source is: The Endosymbiotic Theory was first proposed by former Boston University Biologist Lynn Margulis in the 1960’s and officially in her 1981 book “Symbiosis in Cell Evolution”. Although now accepted as a well-supported theory, both she and the theory were ridiculed by mainstream biologists for a number of years. Thanks to her persistance, and the large volumes of data that support this hypothesis gathered by her and many other scientists over the last 30 years, biology can now offer a plausible explanation for the evolution of eukaryotes.


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