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poler molecules and ions?

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poler molecules and ions?

Postby Decker » Tue Jun 28, 2005 9:45 pm

why cant most polar molecules and ions enter cells? But also alot of food particles are polar, so how do they get in the cell?

(sorry if this is the wrong forum)

Thanks Everyone.
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Postby mith » Tue Jun 28, 2005 9:59 pm

The membrane of the cell is made of phospholipid bilayer.
There are proteins which go thru the membrane.
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Postby James » Tue Jun 28, 2005 10:16 pm

Channel and carrier proteins get around the problem.
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Postby Decker » Tue Jun 28, 2005 10:21 pm

mithrilhack wrote:The membrane of the cell is made of phospholipid bilayer.
There are proteins which go thru the membrane.


could you please explain this further, are you saying that the polar molecules and ions cant enter because the membrane keeps them out? i belive that is what you are saying, if so how do the food particles get through.
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Postby mith » Tue Jun 28, 2005 10:38 pm

Think of it this way:

The membrane is a chain-linked fence. Only really small molecules can pass thru while big molecules can't. To remedy this, the fence has special passages(gates) that allow bigger stuff in(see James's post).
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Postby biostudent84 » Wed Jun 29, 2005 3:06 am

Many ions are smaller than water molecules. And water can definetly get through the membrane.

Ions cannot diffuse through the membrane because overall, the membrane is nonpolar. Ions are repelled away from the membrane.
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Postby chemistry_freako » Thu Jun 30, 2005 2:22 pm

Yeap - the outer layer is hydrophilic (water- loving) due to the phosphate groups, but the inner layer is where the hydrophobic (water- hating) 'lipid tails' are =D
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