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4. Amphipathic Alpha Helices

"Amphipathic" means having both hydrophilic (water loving) and hydrophobic (oil loving) characteristics.

This Chapter continues with the single alpha helix highlighted in the previous Chapter.

  White hemoglobin tetramer (4 protein chains), with one surface alpha helix colored: sidechains
C N O
main chain backbone   Heme.
Most sidechains of this helix that are exposed on the surface are hydrophilic, due to their polar nitrogen and oxygen atoms.
  Here is the isolated alpha helix with its hydrophilic side in front.
  The side of the helix that was buried is hydrophobic (sidechains are all carbon). A helix with one side hydrophilic, and the other side hydrophobic, is called an amphipathic helix.
  A simpler color scheme: Hydrophobic, Polar. All atoms in each amino acid are colored according to its sidechain.
  Beta chain: Hydrophobic, Polar. The alpha helix is colored darker. The buried side of the helix is surrounded with hydrophobic amino acids, and heme (also largely hydrophobic).

Most of the alpha helices in hemoglobin have one of their sides on the surface, exposed to water, and the other buried in the hydrophobic core of a protein domain, so most are amphipathic.

   
     

What Do You See?
  1. What does "amphipathic" mean?
  2. What does "hydrophobic" mean?
  3. What types of heme-protein contacts predominate in the pocket that holds heme?

Get immediate feedback at the practice quiz.

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