A Molecular Machine

ATP Synthase

Dear Readers, the more that I study Cell Biology for my Open University degree, the more drop-jawed with astonishment I become. At the moment we’re looking at how cells manage the energy requirements of an organism, and an integral part of the process is a ‘molecular machine’ known as ATP synthase. I hope you’ll forgive me geeking out a bit here, because I do love to share a factoid!

As you might remember from your biology lessons, energy is managed by the mitochondria, a kidney-shaped organelle which floats around in the watery interior of the cell. To digress here slightly (and to simplify greatly), it’s believed that mitochondria were once free-living bacteria who, back in the most distant days of the evolution of life, were gobbled up by a larger organism, but which continued to live and eventually became an integral part of all of the more complex organisms (a similar thing happened with chloroplasts in plants).

Anyhow, you might also remember that a substance called Adenosine Triphosphate (ATP) is one of the ‘currencies’ of energy, which we need to do any kind of ‘work’ in the cell, from digestion to growth. When the bonds in ATP are broken (into Adenosine Diphosphate plus a free phosphate) it releases lots of energy that can be used to power other reactions. The downside is that the cell also has to synthesise ATP, so that it has a store of energy to use. This is where ATP synthase comes in.

Studded into the inner membrane of the mitochondria is an extraordinarily complicated ‘molecular machine’ called ATP synthase. This is a complex of many different proteins which are formed into 15 subunits, but what astonishes me most is its structure. If you look at the illustration below, what it shows is that the protein actually has a rotor which spins as protons enter it from a space between the inner and outer membranes of the mitochondria  (shown in red). This happens because there’s a higher concentration of protons (H+)  on one side of the membrane than the other, so the protons try to equalise themselves. The passage of the protons causes all sorts of changes to the shape of ATP synthase, and generate the energy which allows it to ‘grab’ ADP and a phosphate, and to make ATP.

This might sound like a lot of old chemistry, but when you consider that the human body has literally trillions of mitochondria at any time, and that each mitochondria can have anything from 100 to 5000 ATP synthase molecules working away, it feels (to me at least) completely staggering. And this is only one part of the complexity of the cell. It seems extraordinary to me that all this is going on, for the most part invisibly, in every living thing. It’s miraculous that any of us can ever get up in the morning.

For a rather neat little animation showing the process, click here.

4 thoughts on “A Molecular Machine

  1. Claire

    This was a nice read. I loved the biochemistry course at university.
    This also reminds me of my mother who helped me to revise for my exams: she impressed me because I then realized how much she knew and how enthusiastic she was about her job as a scientist.

  2. Christine Swan

    I remember this well from my biology degree and the fact that mitochondrial DNA is maternally inherited. It is an incredible feat of evolution. It is also interesting that we classify even single-celled organisms depending on whether they can photosynthesise or not. Symbiotic relationships give us clues to how more complex organisms developed and even humans live in partnership with a whole host of friendly bacteria, harmless nematodes tiny ectoparasites. We cannot photosynthesise so must respire to stay alive. In that respect, without mitochondria, we cease to be. It really is quite incredible when you think about it!

    1. Bug Woman Post author

      My mind is completely blown. I thought cell biology would be a slog, and indeed it is, but is absolutely fundamental to everything else that happens. I do occasionally wonder what would have happened if humans had been able to photosynthesise, but I’m thinking that the energy requirements would have been too high for us to be so active. So much to learn, so little time!


Leave a Reply