Biology and Physical Factors #5: Brownian Motion

At the molecular level, nothing is ever still. Thus, every picture of DNA or proteins is fundamentally flawed – everything is a blur of motion.


Yes, the famous Brownian motion at work. Brown had shown this was not a concept limited to living things only; it was something rooted in physics. It is totally random. Mathematical analysis can predict, on average, how far a particle would move from its starting point if the direction of each step is random. Hence the term “predictable randomness”. Also, the larger a molecule, the less it moves.

 

Ok, how is any of this relevant to biology and life? Raghuveer Parthasarathy explains in So Simple a Beginning:

“(Brownian motion) solves a nagging problem with our discussion of self-assembly.”

In earlier blogs, we saw proteins can arrange themselves into patterns. But Lego blocks don’t do that. What’s the difference? Brownian motion gives the answer – the size (Lego blocks are too large to undergo Brownian motion).

“The recipe for self-assembly, therefore, is not merely physical interactions, but physical interactions together with Brownian motion.”

 

As an interesting aside, this puts a limit on the “speed of thought”. Since thoughts involve molecular movements at their core (and electrical signals), Brownian motion puts a limit on how fast we can think (electrical signals move a lot faster than Brownian motion).

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