Question

lipids mainly phospholipids make up the bulk of the cell membrane. How is the structure of the phospholipid so perfectly paired to the function of the cell membrane?

Answer 1

Lipids contain high energy bonds, and these bonds help to provide the energy to move molecules across the membrane.

Answer 2

^That is not right..

Phospholipids are molecules made of two parts:

1) a hydrocarbon "tail" - it is hydrophobic (insoluble in water), varies in length (# of carbons), degrees of saturation (types of bonds (e.g. single, double)).

2) a polar "head" (in terms of having an electric dipole moment, or electrical charge) - this part is hydrophilic (water soluble), it also highly variable in terms of what the "head" actually is.

These molecules arrange themselves in water so that only the polar "heads" face the water portion and the hydrocarbon "tails" face one another. Two possibilities arise:



So to summarize, phospholipids have two parts that cause them to arrange themselves spontaneously in water to form "bubbles" where only the polar head associates itself with the water molecules and the hydrocarbon/hydrophobic tails are shielded from water. This forms a physical barrier that impedes the flow of many (but not all) molecules and thus it is considered \(semi\)-permeable.