Hydrophobic interactions

Noncovalent interactions can occur between nonpolar molecules as well. Polar molecules interact favourably with other polar molecules.  Therefore, polar molecules will arrange themselves to exclude nonpolar molecules in solution. These interactions will result in the association of nonpolar molecules with one another in aqueous solution, forming hydrophobic interactions. Though noncovalent, hydrophobic interactions are strong forces between molecules. In cells, hydrophobic interactions drive protein folding.

Nonpolar molecules are also held together by weak forces. Because electrons move quickly around the nucleus, there may be momentary differences in charge distribution within the electron clouds of atoms. This results in weak positive and weak negative areas of the electron cloud. The weakly positive portions of the electron cloud of one atom may be attracted to the weakly positive portions of another atom’s electron cloud. These momentary electrostatic interactions between nonpolar molecules are called van der Waal’s forces. Though individually weak, large nonpolar molecules may interact via hundreds of van der Waal’s forces and, collectively, these forces form strong interactions between molecules. In cells, van der Waal’s forces hold the nonpolar portions of lipids in cellular membranes together.

Chemical bonds hold atoms within a molecule together as well as molecules to other molecules. As a result, molecules within cells are arranged in a specific manner to reflect the function of those molecules within those organelles and cells.

Summary:

• Atoms are held together in molecules by chemical bonds
• The electronegativity of atoms affects the chemical properties of the bonds those atoms form with other atoms to form molecules
• Bonds may be covalent or noncovalent
  • Covalent bonds involve the sharing of a pair of electrons
    • Polar covalent bonds form between atoms with different electronegativities
    • Nonpolar covalent bonds form between atoms with similar electronegativities
  • Noncovalent bonds include:
    • Ionic bonds where one atom transfers an electron to another more electronegative atom
    • Hydrogen bonds where one polar molecule is attracted to the opposite partial charges on another polar molecule
    • Strong hydrophobic interactions between nonpolar molecules
    • Weak van der Waal’s forces between nonpolar molecules