Moving to where the energy is

ATPanionChemDrawThe human body is a colony of about 30 trillion cooperating cells, each of which needs to burn energy to survive. Within the cells, a lot of the energy is carried around in the form of a molecule called ATP. A single one of our cells may have ten billion or more molecules of ATP, and these molecules are very dynamic. A single ATP molecule may be used to release its energy, then regenerated only a second later. So, there are huge ATP currents and gradients inside cells. And ATP is a big molecule, its structure is above. From left to right, there are three charged phosphate groups (each with a P = phosphorous), a sugar in the middle, and at the part at the top right is also found in one of the bases in DNA.

So, an interesting open question in biology is: What are the consequences for cells of the fact that they are forced to support a large number of big dynamic ATP molecules? One consequence may be that particles are pulled up ATP gradients (smaller molecules move too fast for this to happen, at least I think so). Another was discussed by the Krishnan and Hyman labs, who pointed out ATP affects the protein interactions that cell rely on to function.

I speculate that particles in cells are pulled up ATP gradients, in a paper that should be published in a week or so, in Physical Review Letters (it is already on arXiv). Physical Review Letters is arguably the most prestigious journal in physics. It was a pleasant surprise when they accepted my, rather speculative, paper. The motion is not caused by the energy carried by ATP, but simply due to interactions between the ATP molecules and the surface of the particle, it is these interactions that pull on the particles.

How the ATP-driven motion contributes to how cells work is unknown. The motion helps these bigger particles move around cells, and this may be useful, but really we don’t know enough of how cells work to know. Although, moving from A and B is clearly essential for many of the thousands of types of molecules and particles inside cells, in many cases we just don’t have good data on how they do this. A living cell is ferociously complex, and so small that we can’t even see it with the naked eye. As result we still have a poor understanding of the basic processes that power cells, and so us.

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