Membranes aren't held together by covalent bonds
- The idea
- Predict
- See it
- Why
- Check
The idea
“The lipids and proteins in a membrane are covalently bonded together, like one big molecule.”
Diagrams draw the membrane like a solid wall built from parts fixed together. A real membrane behaves more like a film of oil on water.
The short version
The mistake: The lipids and proteins in a membrane are covalently bonded together, like one big molecule.
What's actually true: Weak, noncovalent forces hold the membrane together, mostly hydrophobic interactions that keep the tails away from water.
- A phospholipid has a hydrophilic head and two hydrophobic tails. Water clings to itself and to the heads, and crowds the tails together.
- Covalent bonds hold the atoms within each phospholipid. Neighboring lipids are held only by weaker, noncovalent attractions, so they slide past each other.
- Integral proteins stay put the same way. Their hydrophobic middle sits among the tails. Peripheral proteins cling to the surface by ionic and hydrogen bonds.
On the exam: Lipids in a membrane aren't covalently bonded to each other, so the bilayer flows and reseals.