Can a molecule walk?

October 31, 2015 9:58 AM

What is going on in this animation? Is this real?
posted by Tom-B to Science & Nature (6 answers total)

Best answer: Kinesin
posted by swordfishtrombones at 10:12 AM on October 31, 2015 [5 favorites]

Here's a narrated animation that includes clips of the same process - you can see kinesin walking at 3:40 and 5:40, although it's not mentioned by name.
posted by theodolite at 10:20 AM on October 31, 2015 [1 favorite]

This video claims to be directly imaged kinesin proteins migrating along microtubules.

Your cells are scaffolded by a microtubule mesh, which is used to transport resources (amino acids, fats, etc) between the various organelles by using kinesin to drag bags of stuff around (ATP is the fuel, as usual).
posted by pharm at 11:16 AM on October 31, 2015 [1 favorite]

Best answer: Here's the deal with the "walking" - that's more or less how the molecule moves, but what's missing from the animation is the loose "foot" flailing wildly and being bombarded by other molecules until it eventually happens to touch farther along the microtubule and stick.

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.

And apparently molecular biologists can see kinesin in motion:

Here’s the deal: we can actually watch single molecules of kinesin behaving. The typical trick is to use a fluorescent bead, attach that to kinesin, and then record the glowing bead’s movement as it is moving along with optical-trapping interferometry. That’s the problem with Wells’ accusation: we actually see the behavior, and it’s not linear, smooth, and graceful.

From this link.
posted by univac at 11:17 AM on October 31, 2015 [9 favorites]

There's a lot of "just wandering around at random until hitting the right place and then sticking" going on in a living cell. That's part of how protein synthesis happens, for instance. There's a thing called a ribosome which sequences down the messenger RNA, and it has a place in it where the next amino acid needs to go. There are loose amino acids connected to transfer RNA's floating around, and occasionally one of them tries to fit into that position. But if the RNA doesn't match, it floats back out again. If it does match, however, the ribosome stitches the amino acid to the growing protein chain and then sequences one step down the messenger RNA, where it waits.

If it weren't for Brownian Motion, we'd all be dead.
posted by Chocolate Pickle at 11:53 PM on October 31, 2015 [3 favorites]

The other commenter have rightly pointed out that a more realistic view would show some Brownian motion happening, but how much Brownian motion is kind of an open question, tbh. The competing models for how kinesin works are the "Brownian ratchet" model, which has the foot move forward and find its new site by a whole bunch of flailing, and the "power stroke" model, where the forward process is driven by a conformational change in the molecule that flings that back foot forward. In actually, it's likely some of each, but the power stroke model was the explanation of choice for the prof who taught me and my fellow first year PhD students this fall - he liked it so much he climbed up on desks to demonstrate it.
posted by deludingmyself at 7:47 AM on November 1, 2015 [3 favorites]