Question

How do alpha-helices create different surfaces (such as a hydrophobic side)?

Answer 1

Ans. The polar and/or charged R-groups (side chain) of amino acids are exposed at the outer surface of a-helix to maximize interaction with the polar aqueous surrounding (say, cytoplasm).

The non-polar or hydrophobic side chains are held buried at the inner core of cylinder. The hydrophobic residues interact among themselves to stabilize the hydrophobic interaction. Burying the hydrophobic groups in the inner region of helix ensures that there is minimized interaction between the hydrophobic residues and aqueous surrounding that would otherwise destabilize the helix due to repulsive and thermodynamically unstable interactions between hydrophobic side chains and polar water molecules in the surroundings.

# Therefore, a-helices create surface of different polarity by differential orientation of polar (charged) and non-polar residues.