Mitochondria, the powerhouse of the cell! We've all likely heard this and/or have seen the many memes. I'm in training as a mitochondrial biologist so I obviously care about them. But why should you care? Well, check out this quick (less than 2 minutes) chalk talk by the National Science Foundation to find out why and get a general overview of mitochondria.
Here are the main points of the video:
- Mitochondria produce energy for most complex living things including people, plants and animals. This energy is produced in the form of adenosine triphosphate (ATP). TL;DR mitochondria = energy, no energy = death!
- Mitochondria contain their own DNA. Mitochondrial DNA (mtDNA) is inherited from only your mother (there are exceptions, there are always exceptions but it is rare), which also let's us trace back human origins.
Ready to move on?
Okay, let's dive a little deeper. Since we are talking about DNA, let's take a minute to refresh ourselves on the central dogma of molecular biology. And if you didn't know it before, you will now and you'll learn the secret - molecular biology really isn't all that hard. ;)
Okay, let's dive a little deeper. Since we are talking about DNA, let's take a minute to refresh ourselves on the central dogma of molecular biology. And if you didn't know it before, you will now and you'll learn the secret - molecular biology really isn't all that hard. ;)
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| Central Dogma of Molecular Biology |
DNA either undergoes replication, which is making copies of itself, or it gets transcribed into RNA (transcription), which are instructions and tools to make proteins. The messenger RNAs (mRNAs) are then translated by processing machinery called ribosomes into proteins. These ribosomes also use the transfer RNAs (tRNAs) as tools to build the proteins. And lastly there are ribosomal RNAs or rRNAs which are parts of the ribosome itself. This basic overview of the central dogma applies to both the cell and the mitochondria. See?! I told you molecular biology is not that hard!
But let's focus on just the mitochondria. The DNA in the mitochondria (mtDNA), encodes for 13 mRNAs, 22 tRNAs and 2 rRNAs. All of these help build only part of the respiratory complexes, or factories that produce ATP (energy). The mitochondria and the respiratory complexes obviously need a lot more than 13 proteins for it's complex structure/job, so all the other proteins (thousands!) are supplied or transported into the mitochondria by the rest of the cell. The mitochondria have their own ribosomes, called mitoribosomes. My PI (principal investigator aka boss) studies the assembly of mitoribosomes. I, however, am interested in studying mitochondrial RNA its processing. I'll go more into detail on what I study in future posts but for now, I want to introduce one of my favorite tools to study mitochondria.
The SIM!
The SIM is a really high powered microscope (SIM = super illumination microscopy) that let's me not only see the mitochondria but look at the organization within them. Mitochondria are really freaking tiny so that is one heck of a zoom. To put that in perspective, a human hair is about 75 microns (micrometers, um) wide and I'm looking at a 5um level. Here is what this bad boy looks like:
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| SIM Microscope at Stony Brook University Core Facility |
And here is an image of two human cells with nuclei out of frame (that's how zoomed in we are, a whole cell doesn't even fit in the frame). The green outlines the mitochondria by staining for TOM20, a protein that is all over the outer membrane of the mitochondria (mitochondria have two membranes - inner and outer). The red is DNA (remember mitochondria have their own DNA).
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| Mitochondria with SIM |
Please comment below with any questions or suggestions on what you'd like to learn about mitochondria.
Thanks for posting one of your own pictures! It's exciting to see what other students at SBU are doing. I was wondering if you could do a post on mitochondrial DNA? I remember learning that it is only inhered from the mother, it would be interesting to learn more about the importance and uses for it. -Roxana Saravia
ReplyDeleteThanks for the response, I just updated this post to have a longer word count and included a bit more about the DNA. But I definitely think a whole post if not series of posts on solely mtDNA would be warranted.
Delete@Roxana,
DeleteI wrote an (unpublished) paper on the ethics of mitochondrial DNA donation. You see, some bioethicists were concerned that since people identify by their DNA, the donation of mitochondrial DNA -- known as mitochondrial replacement therapy, MRT for short -- would give the recipients identity trouble in their future. If you recall, this was that whole "Three-parent Baby" sensation from a few years ago.
My conclusion was that, assuming the donation to be reasonably safe, and knowing that mitochondrial disease is often a serious matter, MRT would be ethical. I came to this conclusion by arguing that, while people sometimes identify by their nuclear genetics, they do not often do so by their mitochondrial genetics.
As you mention, the inheritance mechanisms are such that they do not follow the common understanding of nuclear genetic inheritance. I concluded, therefore, that this potential (small) impact on identity is unlikely to be of sufficiently substantial harm so as to outweigh the benefits of MRT.