A-helices only form on the surface of water-soluble proteins due to the stabilizing effect of hydrogen bonding with water.
True O
False
The correct answer and explanation is:
The correct answer is False.
A-helices can form in both water-soluble and water-insoluble proteins. The formation of an alpha helix in proteins is primarily driven by the internal hydrogen bonding between the backbone amide group and carbonyl group of the polypeptide chain, rather than interactions with water. In an alpha helix, the carbonyl oxygen of one amino acid forms a hydrogen bond with the amide hydrogen of an amino acid that is four residues earlier in the sequence. This regular, repeating pattern of hydrogen bonding stabilizes the helix structure.
In water-soluble proteins, the hydrophilic (water-attracting) side chains tend to be on the exterior of the protein, interacting with the aqueous environment, while the hydrophobic (water-repelling) side chains are typically buried in the interior of the protein, away from water. This arrangement allows for the proper folding and stabilization of the protein in an aqueous environment.
However, this does not mean that a-helices are exclusively found on the surface of water-soluble proteins. In some cases, a-helices can also be found in the interior of the protein, particularly in membrane proteins, where they interact with the hydrophobic environment of the lipid bilayer. In these membrane proteins, the side chains of the a-helix interact with the hydrophobic core of the membrane, while the hydrophilic backbone remains within the membrane’s interior or forms hydrogen bonds with other parts of the protein.
Thus, while water-soluble proteins may have surface-exposed a-helices, a-helices can also be found in other structural contexts, including those that are not necessarily influenced by direct hydrogen bonding with water.