Why Are Cells the Size They Are? Gravity May Be a Factor 85
carmendrahl writes "Eukaryotic cells, which are defined by having a nucleus, rarely grow larger than 10 micrometers in diameter. Scientists know a few reasons why this is so. A new study suggests another reason — gravity. Studying egg cells from the frog Xenopus laevis, which reach as big as 1 mm across and are common research tools, Princeton researchers Marina Feric and Clifford Brangwynne noticed that the insides of the eggs' nuclei settled to the bottom when they disabled a mesh made from the cytoskeleton protein actin. They think the frog eggs evolved the mesh to counteract gravity, which according to their calculations becomes significant if cells get bigger than 10 micrometers in diameter."
Summary is wrong (Score:5, Informative)
Re:Summary is wrong (Score:4, Informative)
Re:Conversion for the casual reader (Score:5, Informative)
Also, 10 micrometers are:
3.2808399 × 10^-5 feet.
6.18735316522 x 10^9 Plank lengths
1.0936133 × 10^-5 yards.
6.36942675 × 10^-8 itinerary stadia.
5.46806649 × 10^-6 fathoms
1.98838782 × 10^-6 rods
4.97096954 × 10^-8 furlongs
Single Cell Organism Up to 38mm/1.5 inch Diameter (Score:5, Informative)
Re:Think of the children! (Score:3, Informative)
I wouldn't call it easy. Sure, in a relatively non-mobile space station that was reasonably small it would be a trivial problem. However, changing the direction of a spinning object at high speeds is no simple task
For space stations we don't want to change direction drastically, we only want to make minor adjustments. Along the spinning axis is trivial, in any other direction the thrust could be synchronized with the rotation. Depending on how advanced you want it to be you may have to adjust the rotation again after adjusting the direction.
and at a certain size the station would pull itself apart unless it was made of some sort of super strong exotic metal.
The force we are talking about is one earth gravity. That is, the force is no larger than what hanging bridges or building floors already have to deal with. The super strong exotic metal we usually use for this is steel but wood is becoming more popular again.
Plus, a structure like that would be hard to maintain over a long period of time since a self sustaining micro-ecosystem would need a body of water of some sort, and any leaks in the outer hull would then dump the water out into space.
This is no different from what happens when there is a leak in the outer hull of a non-spinning space station. The pressure difference between the inside and the outside of the station is already high enough to cause this.
ect, ect, ect
Well, there are some problems that neither you or I have addressed. The most obvious one is that a small station would have to spin incredibly fast. The common sci-fi solution to this is to use a counterweight on a wire to make it possible to rotate around a point that is placed far out from the station. This in return causes problem with docking since you can't just slowly adjust to the same velocity and spin but have to tangent the station.
A possible solution would be to have an entrypoint at the center of the rotation and have an elevator down to the station. The difference here is that when the elevator is close to the center it can't rely on the gravity the way regular elevators work but might need a bidirectional pull solution.
Another minor problem with a spinning station is that while attached to it you get the same gravitational force so all external maintenance will be done hanging from the station. This means that if you disconnect you will be "falling" away from the station. This might seem like a problem but isn't really more problematic that any other hanging maintenance already done in gravity. Less focus on getting back if you fall and more focus on not falling to begin with.
Re:Why are cells spheres (Score:2, Informative)
Re:ISS (Score:5, Informative)
Scientists have been doing stem cell (mostly plant stem cells, but also some mammalian etc.) growth experiments on the ISS for some years (IIRC six flights so far). Results are interesting. Among other things, perhaps the two most interesting results have been as follows.
In microgravity, cell growth is not limited to 2D. For example, that $250,000 hamburger was made by growing hundreds or thousands of one-cell-thick strips on petri dishes. In space, that is no longer the case. So stem cells can be grown one or two orders of magnitude faster, limited only by the need to get nutrients delivered to each cell and wastes removed.
Some mammalian cells that are very difficult or so far impossible to grow down here on Earth have been shown to grow pretty well up there in microgravity, including some human tissue types.
While some form of life on Earth has encountered and adapted to almost every other environmental condition (temperature, light, pH, etc.), so far as we know no living systems have ever had to deal with microgravity. So when grown in space, the cells basically 'freak out', not knowing what to do, and apparently try turning all of their genes to see what works. This seems to make them more amenable to influence by the environment, such as by adjusting temperature outside the norm for the species. Zero Gravity Solutions [zerogsi.com], a biotech company, is preparing further experiments on the ISS to explore this and related questions. (disclosure: I have a small investment in ZeroGSI.)