Question

What problem do transmembrane proteins encounter in spanning the bilayer? Describe a structure by which transmembrane proteins overcome this problem

Answer 1

Proteins have both hydrophobic and hydrophilic region. Membrane have also hydrophilic and hydrophobic region but majority of the portion of lipid bilayer is hydrophobic. Only the little portion (heads) are hydrophilic while rest all (tail) are hydrophobic. The hydrophobic regions of the protein easily cross the lipid bilayer but the peroblem is the passage of hydrophilic portion through hydrophobic regions (tails) of the lipid bilayer. Thus, in order to span a membrane, the hydrophobic regions of transmembrane proteins pass through the membrane and interact with the hydrophobic tails of the lipid molecules in the interior of the bilayer, where they are sequestered away from water. Their hydrophilic regions are exposed to water on either side of the membrane.

There are various ways in which membrane proteins associate with the lipid bilayer. The most common way is formation of α helix. Alpha helix is Common folding pattern in proteins in which a linear sequence of amino acids folds into a right-handed helix stabilized by internal hydrogen bonding between backbone atoms. By the formation of alpha helix a protein molecule exposes its hydrophilic portion towards the exterior of the lipid bilayer while hydrophobic portions remain with interior surface of lipid bilayer.