Maybe switching a radical from the outer to inner leaflet allows for safe removal or modification of the radical by the cell.

Sometimes atoms or molecules generate radicals which are highly reactive. So there might be some signaling going on.Ģ) To remove potentially dangerous molecules. We know from observation that if it's present in equal numbers on the outer and inner leaflets, the cell is dying. One type of phospholipid, phosphatidylserine, is usually present more on the outside than inside. some phospholipid types are only on the outside membrane.

I can think of several possible answers:ġ) Signaling: though these videos don't mention it much, there are many different kinds of phospholipids and they can be useful for signaling and telling other cells what type of cell this is. This is actually a super cool question, never thought of it. Na + ext^+ Na + start text, N, a, end text, start superscript, plus, end superscript ): Similarly, the charge of an ion makes it too difficult to pass through the nonpolar region of the phospholipid membrane without help from transport proteins. simple sugar - glucose): The size and charge of large polar molecules make it too difficult to pass through the nonpolar region of the phospholipid membrane without help from transport proteins. carbon rings): These rings can pass through but it is also a slow process. So, it's not easy for water molecules to cross, and it is a somewhat slower process. Recall that the interior of the phospholipid bilayer is made up of the hydrophobic tails. water): These molecules can also pass through the lipid bilayer without the help of proteins, but they do so with a little more difficulty than the molecule type above. They don't need proteins for transport and can diffuse across quickly. oxygen and carbon dioxide): These molecules can pass through the lipid bilayer and do so by squeezing through the phospholipid bilayers.

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