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Why Are Cells the Size They Are? Gravity May Be a Factor

Unknown Lamer posted about 7 months ago | from the ten-meters-tall dept.

Science 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."

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85 comments

Think of the children! (5, Funny)

ThatAblaze (1723456) | about 7 months ago | (#44931139)

If I'm reading this correctly, it seems very possible that any children born in space would grow up to look like jabba the hut, since the whole gravety issue would no longer be a problem.

Re:Think of the children! (1, Funny)

ShanghaiBill (739463) | about 7 months ago | (#44931179)

If I'm reading this correctly, it seems very possible that any children born in space would grow up to look like jabba the hut, since the whole gravety issue would no longer be a problem.

Except that it is easy to generate artificial gravity by rotating the space station.

Re:Think of the children! (1, Funny)

fustakrakich (1673220) | about 7 months ago | (#44931287)

The vertigo will have you cleaning up a lot of puke.

Re:Think of the children! (-1)

Anonymous Coward | about 7 months ago | (#44931309)

Hey nigger why are niggers such niggers in the first place, nigga?

Re:Think of the children! (1)

Anonymous Coward | about 7 months ago | (#44931845)

It's a space station, not a dreidel.

Re:Think of the children! (1)

wonkey_monkey (2592601) | about 7 months ago | (#44932311)

What's your point? Do you know how fast a station of a particular size would have to spin to generate a reasonable amount of artificial gravity? Do you know how said motion would affect the vestibular system of the average human?

Re:Think of the children! (0)

Anonymous Coward | about 7 months ago | (#44932601)

African or European station?

Re:Think of the children! (1)

barlevg (2111272) | about 7 months ago | (#44933591)

The first part of your question is easy enough to calculate: a=omega^2*r => omega=sqrt(a/r)

So for earth-normal gravity (although it's likely that Mars- or moon-gravity would suffice), 100m radius ring (or dumbbell), you'd rotate at 0.313 radians per second [google.com] or about 1 revolution every 20 seconds. Can the human body handle that without puking? No idea.

Re:Think of the children! (0)

Anonymous Coward | about 7 months ago | (#44933715)

Not to mention the radius it would need to not cause a substantial differential force gradient in the circulatory system

Re:Think of the children! (2)

barlevg (2111272) | about 7 months ago | (#44934261)

Start with a=omega^2*r

Assume human height is 2m.

So difference in acceleration between your head and your feet will always be: a1-a2=omega^2*r-omega^2*(r- 2m)
a1-a2=omega^2*(2 m)

Assume acceptable acceleration difference is 1 m/s^2 (just for sake of argument and easy computation). Then the maximum omega^2 is 0.5 radians^2/seconds^2.

Assume we want the acceleration at the floor to be 10 m/s^2 (approx. 1 earth gravity). Then using the first equation, we get a radius of 20m.

Re:Think of the children! (2)

ThatAblaze (1723456) | about 7 months ago | (#44931297)

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, and at a certain size the station would pull itself apart unless it was made of some sort of super strong exotic metal.

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. ect, ect, ect.. I wouldn't take long at all for some genius to come up with the bright idea of just not spinning and instead making exercise mandatory. Then out come the jabba babies.

Re:Think of the children! (3, Interesting)

TheLink (130905) | about 7 months ago | (#44931605)

at a certain size the station would pull itself apart unless it was made of some sort of super strong exotic metal.

Attach space station to counterweight with a bunch of long tethers.
Spin to taste.
We've got cables holding up rather heavy stuff down on Earth.
No need to spin at high speeds, no need for big space stations.

Re:Think of the children! (3, Informative)

Anonymous Coward | about 7 months ago | (#44932115)

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:Think of the children! (1)

petermgreen (876956) | about 7 months ago | (#44932413)

A possible solution would be to have an entrypoint at the center of the rotation and have an elevator down to the station.

However if you dock material in the center and move it to the main part of the station you will rob angular momentum from the station as a whole. Similarly moving material to the center to move it will add angular momentum to the station as a whole. Also changes in the mass in the main part of the station will move the center of mass and hence the center of rotation.

Re:Think of the children! (0)

Anonymous Coward | about 7 months ago | (#44934411)

Sure, in a relatively non-mobile space station that was reasonably small it would be a trivial problem.

There's certainly a lower limit to this, though. If you tried to spin the ISS, besides the structural difficulties, you'd have huge issues with the distribution of mass. It's so small and light that occupants moving around would disrupt the rotation.

Re:Think of the children! (1)

icebike (68054) | about 7 months ago | (#44931425)

Except that it is easy to generate artificial gravity by rotating the space station.

Yes, its easy. So easy that all of our space stations rotate to create gravity.
Oh, wait. No they don't, because that only works on extreme diameter ships.

Re:Think of the children! (1)

moteyalpha (1228680) | about 7 months ago | (#44931359)

Didn't you see what happened to the Tardigrades that escaped from the ISS? They have formed a group called the Spacer's Guild. They are rad hard, can live in vacuum and can be their own space ship. Now that I think of it, that might be an interesting space station, very organic punk.

Re:Think of the children! (1)

DigiShaman (671371) | about 7 months ago | (#44931395)

What mammals if any have been born in space? And I mean from the time of fertilization to natural birth. Is it even possible with the help of nursing?

Re:Think of the children! (4, Funny)

icebike (68054) | about 7 months ago | (#44931439)

If I'm reading this correctly, it seems very possible that any children born in space would grow up to look like jabba the hut, since the whole gravety issue would no longer be a problem.

Judging from what I see at Walmart, you don't have to go to space the see Jabba.
The gravity problem is in evidence there as well.

Re:Think of the children! (2)

cripkd (709136) | about 7 months ago | (#44931571)

Wouldn't the cell growth and divison mechanism need at least a few generation untill they "realize" there's no more gravity and they can grow larger?

Re:Think of the children! (1)

ThatAblaze (1723456) | about 7 months ago | (#44931801)

I certainly hope so, or else those astronauts on the space station today are doomed! Doomed I say!

It seems unlikely that this hypothetical problem could affect adults.

Re:Think of the children! (0)

Anonymous Coward | about 7 months ago | (#44935645)

You're reading this wrong. It actually implies that giant frogs come from space.

Re:Think of the children! (1)

interkin3tic (1469267) | about 7 months ago | (#44938537)

There was some concern about the effects of weightlessness. I mean, it's a constant on earth, it makes sense that animals would have used it for some developmental signal. My thesis adviser worked on a collaboration between soviet scientists and US scientists in the 80s, testing if there were any effects on incubating and hatching eggs in microgravity.

Evidently the most interesting result to come out of that study was that quail embryos preserved in vodka are not easy to section for microscopy. Paraformaldeyhde and other fixatives commonly used to study embryology are really dangerous if they can just float around and get in your eye, so the cosmonauts used vodka.

Conversion for the casual reader (2, Funny)

pipatron (966506) | about 7 months ago | (#44931145)

And if it's not obvious (mainly for our SI-challenged readers), 10 micrometers equals 0.01 mm.

Re:Conversion for the casual reader (5, Funny)

Anonymous Coward | about 7 months ago | (#44931305)

Or about 4.97096954 x 10e-8 furlongs

Re:Conversion for the casual reader (0)

Anonymous Coward | about 7 months ago | (#44941021)

Uh, no... I believe you mean 4.97e-8... the e-notation refers to 10^... so x10e-8 is really e-7.

Or just get a website that supports Unicode, and...

That isn't right (3, Funny)

Anonymous Coward | about 7 months ago | (#44931393)

I know micrometers can vary in size, but it seems like 10 micrometers [wikipedia.org] should be around thirty inches long.

Re:That isn't right (1)

Boronx (228853) | about 7 months ago | (#44931703)

That's really putting the micro in micrometer. By estimation, 30 inches is about 0.833 micrometers.

Re:That isn't right (0)

Anonymous Coward | about 7 months ago | (#44940271)

Excuse me, but a METER is 39.3700787 inches. Your 30 inches would be .8 METERS, not micrometers; there are a thousand micrometers in a meter.

Who modded that up? Shame on you!

Re:Conversion for the casual reader (0)

Anonymous Coward | about 7 months ago | (#44931399)

Right because someone who doesn't know how large a micron is will know how large a millimeter is.

Re:Conversion for the casual reader (0)

Anonymous Coward | about 7 months ago | (#44943449)

Milimeters are a common everyday unit. Your ruler has mm's and cm's on the other side from the inches. People tend to have both metric and US tool sets. Screwdrivers, socket wreches etc, come in mm sizing. Even hairclippers have mm on them, along with the inches. So a hairdresser knows how big a mm is. So normal people know what a mm is. Micron's are a specialty unit, that scientists and engineers use, but car mechanics and hairdressers don't need.

Re:Conversion for the casual reader (4, Informative)

Thanshin (1188877) | about 7 months ago | (#44931675)

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

Re:Conversion for the casual reader (2)

DavidD_CA (750156) | about 7 months ago | (#44931717)

And there are 91,440,000 micrometers in a football (US) field.

Glad that's cleared up.

Re:Conversion for the casual reader (1)

fa2k (881632) | about 7 months ago | (#44932673)

and a 10 micrometre stack of CDs could store 5.8 MB of data, that's 4 x 10^-7 times the data contained in books at the library of Congress

Re:Conversion for the casual reader (0)

Anonymous Coward | about 7 months ago | (#44943597)

10 micrometres =
5.87613116 × 10-6 smoots

Re:Conversion for the casual reader (0)

Anonymous Coward | about 7 months ago | (#44931835)

But what is it in thousands of an inch? Aka, engineering units.

we better don't (0)

Anonymous Coward | about 7 months ago | (#44931193)

let shifty eyed salesmen sell us on gravity

Summary is wrong (4, Informative)

postglock (917809) | about 7 months ago | (#44931255)

This makes no sense. Actin is found in practically all eukaryotic cells, including those that are tiny. TFA makes no claim that "frog eggs evolved the [actin] mesh to counteract gravity".

Re:Summary is wrong (4, Informative)

Metachs (3007989) | about 7 months ago | (#44931355)

It isn't referring to generic cellular actin, it's referring to the nuclear actin which the larger cells had a much higher concentration of. Its obvious even if you just read the abstract of the actual article, just not the shitty summary on C&EN.

Re:Summary is wrong (2)

postglock (917809) | about 7 months ago | (#44931635)

Sorry, I was being unclear. I was implying that the Slashdot summary was incorrect. (Which is probably no news.)

Re:Summary is wrong (0)

Anonymous Coward | about 7 months ago | (#44939651)

Human eukaryotic cells are often larger than 10um in diameter. For example, some lymphocytes are as large as 20um in diameter.

ISS (1)

simonbp (412489) | about 7 months ago | (#44931389)

This sounds like a perfect experiment for ISS. They mainly do biological experiments (it's not really a good platform for anything else), and this could be a neat result. CASIS (the ISS science institute) is always looking for new experiments and experimenters for the station.

Re:ISS (4, Informative)

garyebickford (222422) | about 7 months ago | (#44933183)

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.)

Why is settling a problem? (1)

kanweg (771128) | about 7 months ago | (#44931451)

Why is it a problem if the nucleus settles to the bottom of the cell?

Bert

Re:Why is settling a problem? (0)

Anonymous Coward | about 7 months ago | (#44934235)

They just, like, crawl around on the floor helplessly.

Imagine a dog. Now imagine if you broke all its legs except one. It would sort of not be like that at all.

Why are cells spheres (1)

cripkd (709136) | about 7 months ago | (#44931561)

I've just realized (though I'm sure someone smarter than me might have done this before) that the fact that cells are more or less spherical means that they evolved microgravity or while buoyant in a liquid. So it's either the aliens in an ancient station in orbit or earth's oceans.

Re:Why are cells spheres (2)

jkflying (2190798) | about 7 months ago | (#44932147)

Or it could be to minimise their surface area for a given volume?

Re:Why are cells spheres (1)

cripkd (709136) | about 7 months ago | (#44932267)

Of course that's WHY it is, but HOW can you do that if you're not "floating"?
Wouldn't you end up with just a pancake otherwise, since in 2d it's the circle that does the equivalent of what you said?

Re:Why are cells spheres (2)

jkflying (2190798) | about 7 months ago | (#44932365)

By osmosis. Imagine inflating a water balloon, if you pump a heavier fluid like water into it, even in the presence of gravity it will take on a spherical shape. Of course it will be *slightly* deformed, but that's all up to the ratio of weight:surface strength.

Re:Why are cells spheres (2, Informative)

Anonymous Coward | about 7 months ago | (#44932465)

The only cells that are spherical are floating. And not all floating cells are spherical (yeast, for example). The cells of most multicellular organisms take on a shape by adhering to each other to to an extracellular matrix, and they generate internal tension by pulling on the adhesions. When you disaggregate the tissue, the individual cells still try to maintain that tension, but with nothing to pull against tend to pull the cell into a little ball.

Gravity requirement (1)

jfisherwa (323744) | about 7 months ago | (#44931603)

Does this mean that a specific gravity is a requirement for cell formation? Lowering the gravity should allow for larger stable cells up until a certain point, correct?

Re:Gravity requirement (1)

jfisherwa (323744) | about 7 months ago | (#44931643)

And if you believe in panspermia, could this mean an investigation of ancient life cell sizes could give clues as to the specific gravity that designed that cell, hinting at the gravity environment they may have originated from?

Single Cell Organism Up to 38mm/1.5 inch Diameter (5, Informative)

Required Snark (1702878) | about 7 months ago | (#44931701)

Gromia Sphaerica [wikipedia.org]

Gromia sphaerica is a large spherical testate amoeba, a single-celled organism classed among the protists and is the largest in the genus Gromia. It was discovered in 2000, along the Oman margin of the Arabian sea, at depths from 1163 to 1194 meters (3816 to 3917 feet). Specimens range in size from 4.7 to 38 millimeters (0.2 to 1.5 inches) in diameter.

Surface area (4, Interesting)

king neckbeard (1801738) | about 7 months ago | (#44931751)

I was under the impression that surface area played a significant role in this as well, which probably couldn't be easily discounted. The surface area of a sphere is 4 pi times the radius squared while the volume is 4/3 pi times the radius cubed. So, the greater the radius, the greater the ratio of volume to surface area. This usually doesn't scale well, as it means there is more mass to support and less means of getting the input and output needed to support it. I'm not saying that gravity doesn't contribute as well, but that's a fairly difficult barrier as well.

Re:Surface area (1)

minstrelmike (1602771) | about 7 months ago | (#44935867)

I suspect in general the distance from the nucleus to every place else in the cell matters. That's why settling to the bottom is bad.
But volume compared to surface area is a major limiting factor for any biological thing.
And even for the fusion processes of suns. Once the hydrogen fire's pressure eases, the star collapses. Quickly.
It's also why it takes a lot longer to make 4 3d copies on a 3d printer than it does to copy 4 sheets of paper.

This begs the question: (1)

StripedCow (776465) | about 7 months ago | (#44932015)

Why does gravity have the strength it has.

Re:This begs the question: (0)

Anonymous Coward | about 7 months ago | (#44932095)

I thought gravity was the weakest of the four fundamental forces? :P

Re:This begs the question: (1)

minstrelmike (1602771) | about 7 months ago | (#44935885)

Why does gravity have the strength it has.

Ah grasshopper. Gravity has no strength at all.
It is the curvature of space which produces the illusion of strength. ;-)

Planets and life (2)

Sqreater (895148) | about 7 months ago | (#44932719)

Does this mean there is also a "goldilocks size" to a planet for advanced life, even any life to evolve? Can it be at the correct distance from its star, have water, and still be essentially dead? Can a planet look like the Earth but because it is five times the size, be sterile?

Re:Planets and life (1)

foniksonik (573572) | about 7 months ago | (#44932929)

Five times the density, not size. Gravity results from mass rather than volume.

Re:Planets and life (2)

foniksonik (573572) | about 7 months ago | (#44933007)

It's awful when you start with one thought and end with another.

Five times mass rather than size. A planet five times bigger could be less dense eg have less mass for a given volume and therefore have a similar gravity to earth.

Re:Planets and life (1)

Anonymous Coward | about 7 months ago | (#44933855)

Good point. Just to nitpick: A planet's surface gravity is function not simply of it's size (volume), but its mass. That means density must also be taken into account. You could conceivably have a planet smaller than Earth with >1g gravity if it was made of more dense stuff than Earth.

Therefore your question would be about a "Goldilocks mass" rather than a "goldilocks size".

I suspect that life could still evolve under higher gravity conditions, but it would have to develop with smaller cell sizes/ different chemistry / some kind of support scaffolding from the outset. Of course xenobiology is still just a purely theoretical field, so who the hell knows?

Science (0)

Anonymous Coward | about 7 months ago | (#44933617)

Wait, gravity affects the size of things?! Mind = blown.

Neutrally Bouyant. (2)

neorush (1103917) | about 7 months ago | (#44934927)

Couldn't a cell be neutrally buoyant in water negating the effects of gravity? I thought it was something like surface tension keeping these things small, it would also make sense that this mesh would counteract surface tension.

Re:Neutrally Bouyant. (0)

Anonymous Coward | about 7 months ago | (#44941085)

No, they aren't talking about the cells buoyancy, but the buoyancy of components inside the cell. Think of the cell as a water filled balloon you put in a bathtub full of water for your example. What they are talking about are a couple of marbles inside the water-balloon. They sink down to the bottom of the balloon, even if the balloon is otherwise buoyant in the water. Stuff at the top of the cell is much farther from the nucleus and other 'heavier' cell components represented by the marbles, which have sunk down to the bottom end of the cell.

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