Question

In a cell membrane, why is it a phospholipid bilayer not just a single layer?

Answer 1

Do you know about the structure of a phospholipid?

Answer 2

Yes, there are two layers of phospholipids lined up. Their heads face outward, and the legs face inward.

Answer 3

That's the structure of the membrane itself. Because the structure of the membrane depends on the properties of each individual phospholipid molecule in the membrane. So I was asking you what you know about the structure and property of the phospholipid molecules. Sorry for being unclear. :D

Answer 4

Oh there's a head and two tails, the head has a negative and positive charge, but the legs don't.

Answer 5

Exactly. The key is that the head is charged, but the tails are not. The charged head is able to form non-bonded interactions with water molecules but the uncharged tail cannot. They can only form non-bonded interactions with other non-charged molecules like the tails of other phospholipids.

So for that reason it is energetically favourable for the tails to associate with each other and for the heads to associate with water on either side of the membrane.

Answer 6

Non-polar parts stick to other non-polar parts?

Answer 7

That is it exactly.

Answer 8

Oooh, so that's why there is a layer of tails under one layer because the tails stick to each other?

Answer 9

Yes. The non-charged tails can only face each other. And the charged heads can only face water too. So with a bilayer, the tails are happy and the heads are happy.

Answer 10

Okay I understand now, thank you so much! :D

Answer 11

Not a prob. Thanks for working through the problem instead of just asking for an answer!

Answer 12

In the early formation of membranes it was nescessary to have a phospholipid bilayer to have water in the cell. The hydrophilic (water loving) cells point to the outside and inside of the cell and the hydrophobic (water hating) tail point inside. The orientation allows for the membrane to be selectively permeable.