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Why would the phospholipid bilayer want to be polar on the outside and non-polar in the inside? why would it not want to be the opposite?

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  • $\begingroup$ why do you think it would be the opposite? $\endgroup$ – Vance L Albaugh Sep 27 '16 at 18:07
  • $\begingroup$ Well, i'm not exactly positive. Both the interior and exterior are aqueous solutions if i'm not mistaken. So why would one be different from the other. Why wouldn't you want the fatty acid chain to be on top? $\endgroup$ – user34748 Sep 27 '16 at 18:16
  • $\begingroup$ check out this link and see if that helps...look at the picture of the lipid bilayer and think about what its structure is chemically... boundless.com/biology/textbooks/boundless-biology-textbook/… $\endgroup$ – Vance L Albaugh Sep 27 '16 at 18:18
  • $\begingroup$ Possible duplicate of biology.stackexchange.com/q/9261/3340 $\endgroup$ – WYSIWYG Sep 28 '16 at 6:06
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Phospholipids in aqueous solution under the proper conditions organize themselves into micelles and other structures - the minimum energy state. This allows the polar head groups to interact with water in the bulk solution, while the non-polar carbon chains are 'protected' from the polar environment. Water is attracted to water, and the polar head groups are attracted to water, the non-polar carbon chains are excluded.
You can get inverse micelles in non-polar solvents.

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There is a misunderstanding here. The questioner mentioned "Both the interior and exterior are aqueous solutions", which is absolutely correct. However it makes evident he was thinking the non-polar part of the membrane molecules are in contact with the interior of the cell, which is wrong. The non-polar ends of the membrane molecules are entirely inside the membrane, in contact with other non-polar ends of the other layer of the lipid bilayer which forms the membrane. Both the interior and the exterior are in contact with the polar ends of the molecules.

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  • $\begingroup$ so the interior and exterior ends are both polar? $\endgroup$ – user34748 Sep 27 '16 at 18:39
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    $\begingroup$ Yes, the ends facing the interior and exterior are both polar. But membranes have two layers, so there are molecular ends in the middle of the membrane, and the ends in there are non-polar (and thus forced away from the aqueous environments of the interior and exterior). $\endgroup$ – mgkrebbs Sep 27 '16 at 21:28

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