Posted on 05/18/2005 11:23:17 AM PDT by DannyTN
Rotary Clock Discovered in Bacteria
What could be more mechanical than a mechanical clock?
A biochemist has discovered one in the simplest of organisms, one-celled cyanobacteria. Examining the three complex protein components of its circadian clock, he thinks he has hit on a model that explains its structure and function: it rotates to keep time. Though it keeps good time, this clock is only about 10 billionths of a meter tall.
Scientists have known the parts of the cyanobacterial clock. They are named KaiA, KaiB, and KaiC. Jimin Wang of the Department of Molecular Biophysics and Biochemistry at Yale, publishing in Structure,1 has found an elegant solution to how the parts interact. He was inspired by the similarity of these parts to those in ATP synthase (see 04/30/2005 entry), a universal enzyme known as a rotary motor. Though structurally different, the Kai proteins appear to operate as another rotary motor – this time, a clock.
We learned last time (see 09/15/2004 entry) that the parts interact in some way in sync with the diurnal cycle, but the mechanism was still a “black box.” Wang found that the KaiC part, a six-sided hexagonal cylinder, has a central cavity where the KaiA part can fit when it undergoes an “activation” that changes its shape, somewhat like unfolding scissors. Like a key, it fits into the central shaft and turns. The KaiB part, like a wing nut, fastens on KaiB at the bottom of the KaiC carousel. For every 120ö turn of the spindle, phosphate groups attach to the outside of the carousel, till KaiC is fully saturated, or phosphorylated. This apparently happens to multiple Kai complexes during the night.
How does this keep time? When unphosphorylated, KaiC affects the expression of genes. During the night, when complexed with the other two parts, it is repressed from acting, effectively shutting down the cell for the night. Apparently many of these complexes form and dissociate each cycle. As the complexes break up in the morning, expression resumes, and the cell wakes up. When KaiC separates from the other parts, it is destroyed, stopping its repression of genes and stimulating the creation of more KaiC. “In summary,” he says, “the Kai complexes are a rotary clock for phosphorylation, which sets the destruction pace of the night-dominant Kai complexes and timely releases KaiA.” The system sets up a day-night oscillation feedback loop that allows the bacterium keep in sync with the time of day.
Wang shares the surprise that a bacterium could have a clock that persists longer than the cell-division cycle. This means that the act of cell division does not break the clock:
The discovery of a bacterial clock unexpectedly breaks the paradigm of biological clocks, because rapid cell division and chromosome duplication in bacteria occur within one circadian period (Kondo et al., 1994 and Kondo et al., 1997). In fact, these cyanobacterial oscillators in individual cells have a strong temporal stability with a correlation time of several months. (Emphasis added in all quotes.)Wang’s article has elegant diagrams of the parts and how they precisely fit together. In his model, the KaiC carousel resembles the hexagonal F1 motor of ATP synthase, and the KaiA “key” that fits into the central shaft resembles the camshaft. KaiB, in turn, acts like the inhibitor in ATP synthase. “The close relationship between the two systems may well extend beyond their structural similarity,” he suggests in conclusion, “because the rhythmic photosynthesis-dependent ATP generation is an important process under the Kai circadian regulation.”
Need we tell readers what we are about to say? “There is no mention of evolution in this paper.” The inverse law of Darwinese stands: the more detailed the discussion of cellular complexity, the less the tendency to mention evolution.
This is wonderful stuff. The cell is alive with wheels, gears, motors, monorails, winches, ratchets and clocks. Paley would be pleased.
Catching a ball is reactive. I place my hand where I see the ball is going to be. The bees are not reacting. Their "decision" to set the displacement at 35% must be made before they start - not after they see the ball in the air. It is a wholly different matter.
Just to clarify, the calculus I was referring to comes into play when setting the displacement of the pointed tetrahedral apex (on the hidden part of the comb) so that the surface area is minimized - not on the choice of a hexagon (although that minimizes as well).
An even more interesting question is why anything a mathematician develops theoretically in his head should have any application in the real world. For example, sitting at my desk using theoretical math, I could calculate what displacement in a pointed tetrahedral apex would result in a minimum service area. The fact that the result of such theoretical work could be observed in the real world was described by Einstein as a "miracle".
I wonder if cancer cells have this kind of clock!
The "eagle has landed"! We're with you. Stand up, take four steps backward, look straight up, your assignment is revealed in the pattern of the ceiling popcorn.
Get back to us when you have accomplished your assignment. :-)
I remember going over the origins of life exhibit at the Smithsonian Natural History Museum ("Elephant Building" to us natives). Thirty years ago, I only wanted to look at the dinosaurs of course. The study of microfossils is a fascinating subject that it seems no scientists can really agree on. Fossil stromatolites and algal mats are undeniable but it seems one can never be quite sure if itty-bitty dot-structures in a slice of shale or chert qualify as life or mineral grains.
No it is not, and if you can't see that there's no point in continuing. You keep on believing that bees do calculus.
Can someone give me a hand with this one? I don't have much time. But I think some good things will germinate on this one, as this is an infectious find. So lets get our Freepun staph to work on this one. Stop watching TB and lets ferment
some good ones here. But remember not to get too strepped out doing it. Tempis fugit.
This one's a tough cell, Rennes. Tempis fugit, you say? Yes, time really flu by. And how did you know I was watching TB? For your information, it was an old "Dick Van Dyke Show" about the Petrie family.
Anything you might discover in my kid's room would be in bacteria.
ping
Well, I can understand the two day old half eaten cheese sandwich. But the toy incredibles car with removeable action figure and fireable torpedoes is gonna take some explaining.
But I'm sure it's no big deal. Obviously the toy car is here, so it must have evolved. 200 million years ago it was G.I. Joe Jeep.
Don't be cilia. I don't see this as a very fertile breeding ground for puns. Amaeboe splittin' pretty soon but I'm sure a few of you clockwatchers will be here all night moldering over this topic. On the one hand, I would think that you could get rid of these clock germs with just a little Dial soap, but then again, they may take a lickin' and keep on tickin'. I guess only time will tell, and we'll just have to watch. Tocking about it isn't going to solve anything, and you'd have to be cuckoo to think it might.
...That's just my humble opinion...on the face of it.
It's a very minute point, but I second everything you said.
I told you this thread would wind down quickly like a broken clock. It looks like the others in hour group just don't want to baccillus up. Sometimes I honestly wonder what makes them tick. I think I'm just going to leave out a big eon and go punch out....
Hey, what did you expect? It is a one-day(night) clock.
Do you have a pointer to the specifics of how the honeycomb within the hive gets built? Local thermodynamic minima are all very nice, but without accounting for the energy barriers to reconfiguration (e.g. how viscous is the wax when it is first laid down? how close to the equilibrium configuration is it at that point? how quickly does it solidify?) you may be oversimplifying the picture.
Cheers!
"This spud's for you!"
Duh. how does the FIRST cell start?
(Or do E types have no theory for bee'swaxigenesis?)
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