How kinesin actually moves – Pharyngula

How kinesin actually moves – Pharyngula

Recently, Carl Zimmer made a criticism of the computer animations of molecular events (it’s thesame criticism I made 8 years ago): they’re beautiful and they’re informative, but they leave out the critical aspect of stochastic behavior that is important in understanding the biochemistry. He’s talking specifically about kinesin, a transport protein which the animators are particularly fond of illustrating.
Every now and then, a tiny molecule loaded with fuel binds to one of the kinesin “feet.” It delivers a jolt of energy, causing that foot to leap off the molecular cable and flail wildly, pulling hard on the foot that’s still anchored. Eventually, the gyrating foot stumbles into contact again with the cable, locking on once more — and advancing the vesicle a tiny step forward. This updated movie offers a better way to picture our most intricate inner workings…. In the 2006 version, we can’t help seeing intention in the smooth movements of the molecules; it’s as if they’re trying to get from one place to another. In reality, however, the parts of our cells don’t operate with the precise movements of the springs and gears of a clock. They flail blindly in the crowd.
The illusion of directed, purposeful movement is a simplifying shortcut: as Zimmer describes, there actually is a lot of noise in the system, it’s just that the thermodynamics of the interactions promote a directionality to the motion. This is Chemistry 101. I figured that everyone with an undergraduate level of understanding of molecules would be able to grasp this.
I did not take into account willful ignorance, however. Jonathan Wells is angry that anyone dared to question the perfect “stately grace” of molecular machines, and accuses proponents of stochastic motion of Flailing Blindly: The Pseudoscience of Josh Rosenau and Carl Zimmer. He has a Ph.D. in biology, and he doesn’t understand what I just said was Chem 101?