Answer
Internal hydrogen bonds
Work Step by Step
Most transmembrane proteins span the lipid bilayer as alpha helices or beta barrels because these structures allow the polypeptide backbone to satisfy its hydrogen bonding requirements while being embedded in the hydrophobic core of the membrane. In an alpha helix, the polar backbone atoms form internal hydrogen bonds, shielding them from the surrounding lipids.
Similarly, beta barrels form closed cylindrical structures where hydrogen bonds occur between adjacent beta strands, creating a stable, hydrophilic interior and a hydrophobic exterior that interacts favorably with the lipid bilayer.
These conformations are energetically favorable and structurally suited for membrane integration.
