Hydrophilic, polar (phosphate) head
Hydrophobic, non-polar (lipid) tail
Make membranes selectively permeable
Arrange themselves so polar heads point out and non-polar tails point in (micelle)
If there are enough they form phospholipid bilayer
Different membranes have different fatty acids; affect strength and flexibility
Hydrophobic/lipid-soluble and tiny molecules pass easily
Water can’t pass through easily, not hydrophobic
Ions, hydrophilic molecules and large molecules do not move across membranes on their own
Need to be transported across bilayer
