Cell Structures

[Casey]

Just looking through some exam papers and got a fright! Some of this stuff I havn't a clue about and can't find in my txt book!

This question has come up in 2 of the papers I have looked through, it askes how the surface area of a cell changes as a cell grows?

Also Cell Membranes. Things like what is the purpose of it, which is to keep all the organelles in that cell? Also what is the structure of a membrane like and how materials move in and out of the cell, by either passive of active transport.

Anyone that can shed some light on these questions?

[mith]

do a forum search.

[Casey]

Thanks! That page helped a lot! But I still can't find how the surface area of a cell changes as a cell grows. Is it simply that as the cell gets bigger the surface area will get bigger too?

[blcr11]

Surface area is proportional to the square of the radius. So surface area grows more rapidly than the diameter of the cell. If the radius doubles, the surface area quadruples. Volume grows even more rapdily than surface area. Volume is proportional to the cube of the radius, so if the radius doubles, the cell volume increases by a factor of 8.

[Casey]

So if the radius doubles, the surface area increases by x4? then the volume increases by x8?

[blcr11]

That's about the size of it.

[Casey]

Do you know how the it changes while the cell grows?

[blcr11]

Not sure I understand the question. To get larger, you have to add material to the membrane (and even more to the interior)--or else you have to stretch things, but I don't know if that's what you mean.

[Casey]

Is that why a cell can only grow to a certain size? Because the membrane would be too stretched and break?

[blcr11]

I don't think that's the major determinant, though I suppose it can contribute to size limitation. Usually cells will grow until they touch another cell or group of cells, and then they stop growing. This is called contact inhibition and operates for most types of cells in solid tissues. Certainly, calorie restriction can limit cell growth, too.

[Casey]

I must say, you really know a lot about Biology, are you a professor or teacher? If I asked you to descrive a cell membrane, would you just say a double layer of lipids containing proteins? I'm studying hard before exams.

[biofreakhazard]

Hello,
I would describe it (with specificity), an amphipathic phospholipid bilayer with molecules (mainly proteins) embedded within the lipids. And it is selectively permeable. Hope that helps.