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How does a cell know how big it is?

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How does a cell know how big it is?

Postby MrMistery » Mon Mar 02, 2009 3:21 am

We are all taught in high-school/college intro courses that a cell cannot exceed a certain size because of the volume/surface area ratio. Logical enough. However, it is a fact that some cells are bigger than others, and that each cell type has only a narrow range of possible variation. So what is the mechanism that cells use to determine how big they are? Is there one? I'm curious if anyone has addressed this question...
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Postby biohazard » Mon Mar 02, 2009 7:35 am

This is just a guess, but how about the concentration of some intracellular signalling molecule?

If a cell has a baseline production of some such protein, it would then stop synthesizing cell membrane when the concentration of that molecule falls below a level that would trigger the synthesis. So there'd be a some kind of feedback system for cell membrane and/or cytoskeleton production. Of course, the eventual size of the cell would then depend on the baseline activity of the gene for the signalling protein in question.

How does that sound?

I also vaguely remember reading somewhere that certain especially big cells (such as eggs) are so large because they have several copies of genes that affect the cell size by synthesizing more substance for the cell. How this works in practice and how the final cell size is determined, I don't remember.
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Postby plasmodesmata11 » Mon Mar 02, 2009 2:41 pm

I think it's concentration of cAMP. I agree with the above explanation. Feedback loops seem logical... This is based on that when you culture something in a petri dish, it will stop growing, like e. coli. The chemical messenger that tells cells that there is no room and they need to stop dividing, in this case, is cAMP. Based on that, I would think that it is similar in regulating its individual size.
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Postby MrMistery » Tue Mar 03, 2009 12:59 am

the concentration of cAMP? Hmm, i find that a little hard to swallow. it seems logical enough for me that all cells have the same mechanism for determining size (such a crucial thing is probably something evolution selected for fairly early). But if we assume that is cAMP, then how come cells who constantly alter the cellular concentration of cAMP don't go haywire? A protein molecule seems to be much more likely..
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Re: How does a cell know how big it is?

Postby JorgeLobo » Tue Mar 03, 2009 11:42 am

agree with MrMystery re. simple explanation of cAMP and dispute that a volume/surface area mathematical limit is effectively the control element. Coenocytic fungi are effectively huge continuous cells (with no crosswalls) as are some life stages of so-called slime molds.
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