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Jon Lund Steffensen
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Smallest rotary motor in biology, the ATP synthase. All the work done in your body is fueled by breaking a chemical bond in ATP, the “currency of energy”. Did you know that you convert your body weight (or an estimated 50 kg) of ATP per day?!

Where does this ATP come from? It is synthesized by an incredibly sophisticated molecular machine, the ATP synthase, embedded in the inner membrane of our mitochondria. Energy from the oxidation of food results in protons being pumped across the membrane to create a proton gradient. The protons drive the rotation of a circular ring of proteins in the membrane that in turn move a central shaft. The shaft interacts sequentially with one of 3 catalytic sites within a hexamer, making ATP (little butterflies in the movie!). The ATP synthase rotates about 150 times/second

To visualize the rotation under a microscope, a very long fluorescent rod (actin filament) was chemically attached to the central shaft. Watch real movies (not animations!) of the enzyme spinning here: http://www.k2.phys.waseda.ac.jp/F1movies/F1long.htm

Notice the rotation is slower with longer rods. The rotor produces a torque of 40 pN nm (40 pico Newtons x nanometer), irrespective of the load. This would be the force you would need to rotate a 500 m long rod while standing at the bottom of a large swimming pool at the rate shown in the movie.

How did this amazing rotor evolve? The hexameric structure is related to DNA helicases that rotate along the DNA double helix, using ATP to unzip the two strands apart. The H+ motor has precedence in flagella motors that use proton gradients to drive rotation of long filaments, allowing bacteria to tumble through their surroundings. At some point, a H+ driven motor came together with a helicase like hexamer to create a rotor driving the hexamer in reverse, to synthesize ATP.

The 1997 Nobel prize in Chemistry was awarded to John Walker and Paul Boyer for solving the structure and cyclical mechanism of the ATP synthase, respectively. This amazing enzyme was also the subject of my own Ph.D. thesis, and my first love!

For #ScienceSunday curated by +Allison Sekuler and +Robby Bowles .
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With holiday dinner leftovers still stocked up in your fridge, undoubtedly many of you are lying prostrate on the couch trying to recover from the feasting. While it has long been held that eating copious amounts of turkey tends to make one sleepy, it seems this urban legend is not quite as accurate as I thought.

Regardless, there is bound to be plenty of napping this weekend. Something about lots of good food, wine, a warm fire, and quiet music just seems to knock me out. It’s certainly nothing to feel guilty about, as napping is a perfectly normal and healthy activity, and is something we should all probably do more of.

Check out this infographic by PatioProductions.com, sharing some interesting factoids on napping and how it is regarded in various societies.
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